JOIN operator. JOIN join operator Inner join, INNER JOIN

According to the compatibility horoscope, the Pisces man is very charming. He always sees the best side of women, because Pisces is an incorrigible romantic.

Compatibility Pisces Man - Taurus Woman

In terms of compatibility, the Taurus woman and the Pisces man are an amazing couple. They are both similar and not similar at the same time. They look at how different they are and notice similarities.

This couple has several fundamentally important issues on which they have different opinions. If in everyday communication they do not argue about them, then they have every chance to live a happy life together. Oddly enough, more often the fate of a couple does not depend on the constant and firmly standing female Taurus, but on the fluid and changeable Pisces.

Such an alliance is especially good for the Pisces man: in the Taurus woman, he usually finds the necessary mutual understanding and support. She willingly takes over the management of the household, is able to make decisions and take on an organizational role in the family (which Pisces men do not like and do not know how to do), and even if necessary, can earn more than him in order to support the family ...

Compatibility Pisces Man - Gemini Woman

According to the compatibility of the Gemini woman and the Pisces man, the dreamy philosopher Pisces man and the expansive Gemini woman are so different that it seems that nature created them with the intention that their paths would never cross. Usually they do not intersect, but there are exceptions to any rule.

The relationship between Gemini and Pisces is full of conflict and misunderstanding.

Pisces is a symbol of intuition and fantasy, and Gemini is of reason and erudition. It is difficult for them to find common ground. If for some reason they nevertheless agreed, the union promises to be original and bright ...

Compatibility Pisces Man - Cancer Woman

According to the compatibility of Cancer women and Pisces men - between this pair there can be not only harmonious friendship or favorable cooperation, but also deep, mutual love, happy marriage. And love often breaks out here even "at first sight." Both Cancer and Pisces feel good in this union.

A Cancer woman may initially think that she would be happier with a stronger man. But the longer she lives with a Pisces man, the more clearly she understands that she would hardly get along with someone who would be stronger than her, as well as with soft dreamy Pisces.

Pisces man and Cancer woman are very similar and therefore understand each other perfectly. In their life together, there is usually no place for scandals and quarrels, although you cannot call their relationship dry: they are wonderful lovers, together they are easy and good. A Cancer-Pisces couple is a union of two dreamers and dreamers with a rich inner world...

Pisces Man - Leo Woman Compatibility

According to the compatibility of the Leo woman and the Pisces man, the marital relationship between them can be happy and long. The Pisces man does not get tired of admiring the Lioness and showering her with compliments, and the Leo woman bathes in the love of Pisces and regally accepts worship.

The main condition for a long relationship is that the Lioness is not tired of being a constant leader and carrying all the responsibility, and Pisces does not suddenly wake up “male pride”.

Of course, it won't be without difficulties. In life together, the Lioness is usually not satisfied with Pisces' indifference to career and money, as well as his unwillingness to organize his life. Most often, this results in claims on her part and family conflicts ...

Compatibility Pisces man - Virgo woman

According to the compatibility of Virgo women and Pisces men, this couple has much more prospects in friendship and cooperation than in love. The Virgo woman and the Pisces man can give each other many invaluable life lessons, share experiences, work in the same area, but there are too many things in life together that separate them. Life under one roof can become a source of misunderstanding and conflict for the demanding worker-Virgo and the not-too-practical, vulnerable Pisces man, which is why their union rarely turns out to be lasting. But they will always be drawn to each other. These are two completely different people who, probably, will not be able to fully understand each other until the end of their lives ...

Compatibility Pisces Man - Libra Woman

According to the compatibility of Libra women and Pisces men, relationships in this pair can work out well. Both partners are united by a love of beauty. The Libra woman in this union receives so much warmth and tenderness, affectionate words and attention from the Pisces man, as, perhaps, from no other of all the signs of the Zodiac. And the Pisces man, in alliance with the Libra woman, finds a quiet, comfortable haven.

Quarrels in a pair of Libra-Pisces begin because of money. A Pisces man usually does not know how to make money. The only exceptions are those who have found their calling. And the Libra woman is used to living in comfort, and is not ready to limit herself to small things. In a stable environment, she herself knows how to make good money. But, if there was a crisis, she is helpless. And besides this, the Pisces man cannot support her. Therefore, often couples of a Libra woman and a Pisces man break up during financial crises ...

Compatibility Pisces Man - Scorpio Woman

According to the compatibility of the Scorpio woman and the Pisces man, they can have a wonderful family life. They are well suited to each other, understand, complement and help to cope with the problems of each of them, if they arise.

In family life, a Scorpio woman most often takes on an organizational role and masterfully solves the problems that arise. She has many desires and very high demands on the Pisces man. In everyday life, she can put a little pressure on the Pisces man, encourage him to achieve more. It is worth noting that this often has the most positive influence. The Pisces man does not resist the tough and firm demands of his wife, since until the end of his life he remains just a “fish”, able to live only in a well-maintained aquarium, warmed by spiritual warmth. In addition, you can always rely on a Scorpio woman in everything ...

Compatibility Pisces Man - Sagittarius Woman

According to the compatibility of the Sagittarius woman and the Pisces man, their union is quite rare, and it can rightfully be called the union of opposites. Pisces men are accustomed to calmly go with the flow and trust fate to solve their problems. And the Sagittarius woman is active, energetic, and in case of problems she is used to acting, and not waiting for “weather from the sea”. due to such a different approach to life, it is difficult for them to understand each other.

In family life, the Sagittarius woman, as a rule, tries to stir up the Pisces man, however, almost always, she achieves the exact opposite result. However, if Sagittarius truly loves his Pisces man, then she is able to appreciate in him his inner harmony, talent and kindness. In addition, the Sagittarius woman and the Pisces man have good sexual compatibility ...

Compatibility Pisces Man - Capricorn Woman

In terms of compatibility, the Capricorn woman and the Pisces man are just perfect for each other. They live happily together and absolutely do not see any shortcomings in each other.

In addition to the fact that the Capricorn woman and the Pisces man have a great spiritual and intellectual similarity, they also have a strong physical attraction to each other.

In the family union of Capricorn and Pisces, a woman often plays the role of leader in the family. She is a support for her own family and knows how to throw a life jacket to her partner in time...

Compatibility Pisces Man - Aquarius Woman

According to the compatibility of Aquarius women and Pisces men, in order for their union to be harmonious, both spouses will have to spend a lot of effort. Aquarius woman and Pisces man have a lot in common. They are childishly sincere, have an admiring look at the world around them, are emotional, there are many fantasies and dreams in their lives. Both are idealists, both do not want to fit into everyday reality with its petty worries, joys, salaries, desire for career growth, vacation according to the schedule and creativity according to the template. It would seem that they found each other. But no. They are simply "not of this world" - they are from different worlds and even despite the commonality of interests, it is difficult for them to understand each other.

The Pisces man is passive, and with this behavior he displeases the Aquarius woman. She wants a brighter and more active life. And the Pisces man is immersed in himself and loves to philosophize ...

Pisces Man - Pisces Woman Compatibility

The compatibility union of the Pisces woman and the Pisces man can rightly be called happy and strong. They get along well with each other, together they are never bored. In this union, both find their "half". They have an amazing similarity of characters that will delight, not disturb, as they perfectly understand what their partner is doing and thinking. Both for the Pisces woman and for the Pisces man, emotions are very important in a relationship. And something, something, so this each partner can give in abundance. Both spouses have calmness, compliance, sensitivity, as well as independence, dreaminess, and impracticality.

What will be the relationship between the Pisces man and the Pisces woman is difficult to describe, since in each case they will be individual and unique, like themselves. The only thing that all Pisces couples have in common is that they just go with the flow serenely...

Operator JOIN is used to perform a join operation on data from two sets into one result set. Several may be used different types join operations when executing SELECT . Which rows are included in the result set depends on the type of join operation and on the explicit join condition. Connection condition, i.e. the condition for matching table rows with each other is a logical expression.

If you need to join multiple tables, the join operation must be applied consecutively several times.

Syntax of the JOIN operator

Syntax for connecting to an additional table query using the operator JOIN can be presented in the following form:

SELECT field1, field1, [,...n] FROM Table1 t1 (INNER | (LEFT | RIGHT | FULL) OUTER | CROSS ) JOIN Table2 (ON | USING(field_name[,...n]))

In most DBMS, when using the operator JOIN in combination with the keywords LEFT, RIGHT, FULL, the OUTER operand can be omitted. The INNER operand can also be omitted in most DBMSs.

If the names of the columns by which the tables are joined are the same, then instead of ON you can use USING. For operator CROSS JOIN condition is not specified.

Test tables for JOIN validation

For further examples, let's create two simple test tables. Reference tables of users and their cars. The first table will store the user ID and his name (nick). The second table contains a list of cars (identifier, name) and the identifier of their owners/users. It should be noted that the user may have several cars or none at all.

User Table

CREATE TABLE users (id int not null, name varchar(32) not null, primary key (id)); -- Insert some records into the table insert into users (id, name) values ​​(1, "alex"); insert into users (id, name) values ​​(2, "piter"); insert into users (id, name) values ​​(3, "serg"); insert into users (id, name) values ​​(4, "olga"); insert into users (id, name) values ​​(5, "ostap");

Car table

CREATE table autos (id int not null, -- auto id name varchar(32) not null, -- auto name oid int not null, -- primary key owner id (id)); -- Insert several records into the table insert into autos (id, oid, name) values ​​(1, 1, "toyota camry"); insert into autos (id, oid, name) values ​​(2, 1, "toyota prado"); insert into autos (id, oid, name) values ​​(3, 2, "renault megane"); insert into autos (id, oid, name) values ​​(4, 3, "nissan x-trail"); insert into autos (id, oid, name) values ​​(5, 4, "suzuki swift"); insert into autos (id, oid, name) values ​​(6, 4, "suzuki vitara");

Inner join, INNER JOIN

INNER JOIN is an inner join operator between two tables. It is symmetrical, so the order of the tables is not important to the operator.

Applies INNER JOIN to get only those rows for which there is a match between the records in the main table and the join table. Algorithm for generating the result: each row of the main table is compared with each row of the attached table. After that, the connection condition is checked. If the condition is true, the corresponding "joined" row is added to the result set.

Query with result set column selection select u.name as owner, a.name as auto from users u inner join autos a ON a.oid = u.id -- Query result owner auto alex toyota camry alex toyota prado piter renault megane serg nissan x-trail olga suzuki swift olga suzuki vitara -- Query without selecting result set columns select * from users u inner join autos a ON a.oid = u.id -- Query result id name id1 name1 oid 1 alex 1 toyota camry 1 1 alex 2 toyota prado 1 2 piter 3 renault megane 2 3 serg 4 nissan x-trail 3 4 olga 5 suzuki swift 4 4 olga 6 suzuki vitara 4

To get data that does not match the condition, you need to use an outer join - OUTER JOIN.

Outer join, OUTER JOIN

When joining two tables with the operator OUTER JOIN the result set will necessarily include rows of either one of the tables, or both tables. The OUTER keyword can be omitted. A LEFT JOIN entry is identical to a LEFT OUTER JOIN.

There are two types of outer join. it LEFT OUTER JOIN and RIGHT OUTER JOIN. These operators work in the same way. The difference is that when using LEFT JOIN, the main table is the table specified after the FROM statement. The data of the attached table is added to the rows of this table under the given conditions. For the RIGHT OUTER JOIN operator, everything is exactly the opposite.

Outer join operator OUTER JOIN is not symmetric, so the order in which relationships between tables are established is important for the operator.

LEFT OUTER JOIN statement example

Select u.name as owner, a.name as auto from users u left join autos a ON a.oid = u.id -- Query result owner auto alex toyota camry alex toyota prado piter renault megane serg nissan x-trail olga suzuki swift olga suzuki vitara ostap

Graphically, the result of the work can be represented as follows:

LEFT OUTER JOIN operator with filtering

By adding the condition "where a.name is null" to the code of the previous example. Only one "ostap" entry will remain in the selection, since only it does not have a car defined.

Graphically, the result of the work can be represented as follows:

Cross join operator, CROSS JOIN

CROSS JOIN is a cross join operator (cartesian product). The statement is symmetrical and the order of the tables for the statement is unimportant.

The resulting set is formed as follows: each row of one table is connected to each row of the second table, thereby giving as a result all possible combinations of rows of two tables. For our example, this results in 30 rows of the result set.

Select * from users cross join autos -- Query result id name id1 name1 oid 1 alex 1 toyota camry 1 2 piter 1 toyota camry 1 3 serg 1 toyota camry 1 4 olga 1 toyota camry 1 5 ostap 1 toyota camry 1 1 alex 2 toyota prado 1 2 peter 2 toyota prado 1 3 serg 2 toyota prado 1 4 olga 2 toyota prado 1 5 ostap 2 toyota prado 1 . . .

The set results show only the first 12 rows.

According to the compatibility horoscope, the Pisces man is very charming. He always sees the best side of women, because Pisces is an incorrigible romantic. The Pisces man has a rare talent in this world: he knows how to be happy. Moreover, he is capable of this not only in the Sultan's palace, but also in the notorious hut. His serenity, talent, compassion, kindness can attract you like a magnet, but know that the Pisces man is by nature not a leader, but rather a follower. Before you appeared, he was led through life by Fate, parents, friends, but now it's your turn.

It just so happened that the life success of the Pisces man largely depends on how the circumstances develop. Or on how decisively those who are next to him will act. It's just that he often confuses his inner world with the outer one. By and large, everything suits him anyway, but you do not succumb to his relaxation. Remember: the Pisces man has a huge potential, which he can successfully realize with your help.

If you succeed in impressing the Pisces man with the need to act decisively, there is every chance that your house will be a full bowl. The talent and innovative thinking of Pisces are able to elevate him to the very heights. If he does not have the necessary incentives in time, he will also serenely enjoy life, but most likely already without you. And it’s not at all because he will part with you, it’s just that you yourself are unlikely to be able to live on his salary as a school librarian. However, if you still choose heavenly life in a hut next to the Pisces man, you will be surprised that in many ways the saying will turn out to be true. Unlike many other men, Pisces men have a lot of virtues more valuable than a fat wallet.

According to the compatibility of the Pisces man - who, if not him, is able not only to listen to you, but literally look at the world through your eyes? His empathy will be so complete that he will take some of your problems on himself. At the same time, the Pisces man is delicate, laconic, knows how to perfectly keep secrets. He is so capable of penetrating other people's feelings that he is simply not able to judge anyone. After all, he sees a person through and through, which means that he understands all the deep motives of his actions!

Take the Pisces man with you when you are going to an exhibition or a concert. When he is near you, you will be surprised to notice that your perception of beauty has become deeper and brighter. And the thing is that, exchanging impressions of a picture or music with him, you are immersed in a world where Pisces has no equal.

However, the ability of the Pisces man to feel subtly has its downside. Get ready for the fact that those around you will alternately cry into his vest, confide their secrets, or simply dedicate to all the vicissitudes of their lives. Pisces takes this state of affairs for granted, although this not only takes up his time, but also causes emotional devastation. So you will sometimes have to take on the role of Cerberus, driving annoying friends away from him.

In everyday life, the Pisces man (however, like many representatives of the stronger sex) is far from ideal. He is rather absent-minded and considers it normal to take off his shoes and leave his shoes right there, in the middle of the corridor. However, if you sharply or even just grumpily make a remark to him, he may be offended and shut up for a long time. Do not forget that Pisces is very vulnerable and easy to offend.

With compatibility in love and marriage, the Pisces man is a talented dreamer. The thin strings of his soul, like a Stradivarius violin, are capable of extracting the most beautiful and gentle sounds. To hear them, stock up on love, gentleness and patience. And most importantly, never play with his feelings or dreams - he will not forgive you for this.

Pisces Man with Other Signs

Pisces man and Aries woman- Relationships in this pair largely depend on which of the two types of characters the Pisces man is: a drifting philosopher or a purposeful creator. In the first case, the chances of their life together are almost zero: a practical and active Aries woman will always try to remake Pisces, which will quickly lead to a break. The second case is much more favorable: the Aries woman, being a romantic at heart, is able to see her ideal man in Pisces - talented, with a rich inner world. In this case, all domestic issues in their pair are easily resolved: the Aries woman takes the reins of house management into her energetic hands, giving Pisces the freedom of creativity. Such a union is harmonious and able to last a lifetime.

Pisces man and Taurus woman- Such an alliance is especially good for the Pisces man: in the Taurus woman, he usually finds the necessary understanding and support. She willingly takes over the management of the household, is able to make decisions and take on an organizational role in the family (which Pisces do not like and do not know how to do), and even if necessary, she can earn more than him to support her family. Of course, the Taurus woman is not always happy with this state of affairs, but in Pisces she is admired by his kindness, talent and serenity. In addition, they have excellent sexual compatibility and many similarities: they both love nature, hate quarrels, and their relationship has every chance of being long and strong.

Pisces man and Gemini woman- The dreamy philosopher Pisces and the expansive Gemini woman are so different that it seems that Nature created them with the intention that their paths would never cross. Usually they do not intersect, but there are exceptions to any rule. In a joint life, neither Pisces nor the Gemini woman are usually set up for frankness and transparency in relationships. Lack of understanding, silence, secrets from each other and sometimes even deceit - all this they both, as a rule, consider to be quite justified in the family, and therefore their union rarely turns out to be lasting. However, it also happens that Gemini and Pisces deliberately turn a blind eye to the secrets of their partner, thereby prolonging their mysterious marriage.

Pisces man and Cancer woman- This is a union of two dreamers and dreamers with a rich inner world. Pisces man and Cancer woman are very similar and therefore understand each other perfectly. In their life together, there is usually no place for scandals and quarrels, although you cannot call their relationship dry: they are wonderful lovers, together they are easy and good. By itself, the Pisces man is impractical, but in life with the Cancer woman, he, as a rule, begins to bring a lot more money into the house and generally becomes more responsible and rational. Cancer, on the other hand, is able to diligently manage the household and raise children, so that their calm family life, full of tenderness and mutual understanding, can be called almost perfect.

Pisces man and Leo woman- Such an alliance is extremely rare: the paths of the dreamer-Pisces and the energetic Lioness almost never intersect. Almost the only thing that can sometimes unite them is an innate sense of beauty, which is much more developed in Pisces. In life together, the Lioness is usually not satisfied with Pisces' indifference to career and money, as well as his unwillingness to organize his life. Most often, this results in claims on her part and family conflicts. However, if the Pisces man is rich, his “cons” for the Lioness turn into “pluses”: she can spend as much as she wants on herself, manage his affairs and actually be the head of the family, since he cares little about such trifles. Moreover, it is also ideal for him. In this case, their marriage can happily last a lifetime.

Pisces man and Virgo woman- It is interesting that such an alliance has much more prospects in friendship and cooperation than in love. Virgo and the Pisces man can give each other many invaluable life lessons, share experiences, work in the same area, but there are too many things in life together that separate them. Life under one roof can become a source of misunderstanding and conflict for the demanding worker-Virgo and the not-too-practical, vulnerable Pisces man, which is why their union rarely turns out to be lasting.

Pisces man and Libra woman- This is a rather complicated alliance, in which it is sometimes difficult for partners to understand each other. The Libra woman is unhappy with the impracticality of Pisces and his unwillingness to subordinate his life to some clear goal. This dissatisfaction she, being in a bad mood (which she has regularly), with all frankness, is able to express him directly to his face. Pisces, on the other hand, prefers to silently listen to her accusations and endure, driving grievances inside. However, even if their relationship has long been on the verge of breaking up, neither the Pisces man nor the Libra woman, as a rule, is in a hurry to break them off because of their dislike for sudden steps. Because of this, their marriage can drag on for many years due to habit alone. To prevent this from happening, Libra needs to curb his temper, remembering that there are also a lot of things that unite them: they have good sexual compatibility and a real talent to feel beautiful in all its manifestations. Together they have a great time in nature, at exhibitions, in theaters. Sometimes their relationship is stronger if Pisces and Libra are not in a hurry to get married, but remain lovers or just friends.

Pisces man and Scorpio woman- In general, this is a successful union, because the sensitive Pisces man and the Scorpio woman have excellent sexual compatibility. However, in addition to this area, they have much in common: both are tuned to serious relationship and value fidelity and constancy in a partner. In everyday life, a Scorpio woman can put a little pressure on Pisces, encouraging him to achieve more, and often this has the most positive effect on him. Scorpio herself is able to take on an organizational role in the family, skillfully solving current problems and tasks. In their relationship there is love, and friendship, and mutual understanding, so that they can last for many years.

Pisces man and Sagittarius woman- This is a rather rare union of two complete opposites: a Pisces man, calmly going with the flow, and an active, energetic Sagittarius woman. Despite the fact that Sagittarius and Pisces have good sexual compatibility, it can be difficult for them to understand each other: Sagittarius is used to acting, and Pisces usually relies on Fate in solving problems. In a life together, a Sagittarius woman, as a rule, tries to stir up Pisces, but often achieves only the opposite result. However, Sagittarius is fully able to appreciate in Pisces his inner harmony, talent and kindness, and although this does not make their union ideal, it adds a lot of positive to it.

Pisces man and Capricorn woman- Outwardly, this union often looks ideal, although in reality it is not always so. The philosophically inclined Pisces man and the Capricorn woman, with her love of order, are too different to understand each other well. Capricorn strives to achieve great heights in life, and Pisces' indifference to money, career and fame cannot but embarrass her. Often she tries to put pressure on him, encouraging him to act, but she has too little chance of getting her way. On the other hand, she is set for a long-term relationship, and until the last she does not intend to break them. Pisces also do not like to take sudden steps, so this pair can only exist by virtue of many years of habit. However, in the case when Pisces still shows perseverance and energy in business, their living together getting better.

Pisces man and Aquarius woman- In this union, the Pisces man and the Aquarius woman have a lot in common: they are connected by a childishly sincere, admiring view of the world, emotionality, the ability to fantasize, a subtle sense of beauty. This can be a wonderful creative union in which the spouses are busy with one common cause. However, despite the mutual understanding and similarity of interests, Aquarius is able to experience dissatisfaction with the not too active behavior of Pisces. As a rule, she wants to lead a brighter and richer life, and this is difficult for her philosophically minded chosen one to understand. Often this becomes the reason that over time, the Aquarius woman begins to get bored and burdened by family ties, so Pisces, in order to avoid a break, needs to take the initiative in time and share with her at least some of her many hobbies and hobbies.

Pisces man and Pisces woman- In this union, Pisces, as a rule, find their "soul mate", and what if this half is also independent, dreamy, sensitive and not very practical? Simply, the relationship of two Pisces serenely floating with the flow will be as unique and individual as they are. Both in everyday life and in obligations to each other, Pisces are unlikely to become an example of an ideal family for others - there can be too many omissions, fantasies and secrets between them. Even having lived side by side all their lives, Pisces often remain a mystery to each other. And yet, in spite of everything, together they are able to feel the real kinship of close souls and the need for each other. The rest is usually irrelevant to them.

The development of any database implies not only the creation and filling of tables with various information, but also further work with the data. To correctly perform various tasks of selecting data from tables and generating reports, the standard Select construct is used.

Data selections from tables

If we consider the task of selecting data or building some report, we can determine the level of complexity of this operation. As a rule, when working with serious (in terms of the amount of information) databases that are formed, for example, in online stores or large companies, the data selection will not be limited to only one table. As a rule, selections can be made from a fairly large number of not only interconnected tables, but also nested queries / subqueries that the programmer himself makes, depending on the task assigned to him. To select from one table, you can use the simplest construction:

Select * from Person

where Person is the name of the table from which to fetch data.

If there is a need to select data from several tables, you can use one of the standard constructions to join several tables.

Ways to connect additional tables

If we consider the use of such structures at the initial level, then we can distinguish the following connection mechanisms required amount tables for sampling, namely:

1. Inner Join operator.
2. Left Join or, this is the second way of writing, Left Outer Join.
3. cross join.
4. Full Join.

The use of table join operators in practice can be learned by considering the use of the SQL operator - Inner Join. An example of its use would look like this:

Select * from Person

The SQL language and the Join Inner Join operator can be used not only to join two or more tables, but also to connect other subqueries, which greatly simplifies the work of database administrators and, as a rule, can significantly speed up the execution of certain complex queries.

Combining data in tables row by row

If we consider connecting a large number of subqueries and assembling data into a single table row by row, then the Union and Union All operators can also be used.

The use of these structures will depend on the task set for the developer and the result that he wants to achieve in the end.

Description of the Inner Join Operator

In most cases, the Inner Join operator is used to join multiple tables in SQL. The description of Inner Join in SQL is quite simple to understand for the average programmer who is just starting to understand databases. If we consider the description of the mechanism of operation of this design, we get the following picture. The logic of the operator as a whole is built on the possibility of crossing and selecting only the data that is in each of the tables included in the query.

If we consider such work from the point of view of graphical interpretation, we get the structure of the SQL Inner Join operator, an example of which can be shown using the following diagram:

For example, we have two tables, the schema of which is shown in the figure. They, in turn, have a different number of entries. Each of the tables has fields that are interconnected. If you try to explain the operation of the operator based on the figure, then the returned result will be in the form of a set of records from two tables, where the numbers of the related fields match. Simply put, the query will return only those records (from table number two) that have data in table number one.

Inner Join Operator Syntax

As mentioned earlier, the Inner Join operator, namely its syntax, is extremely simple. To organize relationships between tables within the same selection, it will be enough to remember and use the following basic scheme for constructing an operator, which is written in one line of the program SQL code, namely:

• Inner Join [Table name] on [key field from the table to which we are connecting] = [Key field of the table to be connected to].

For communication in this statement, the main keys of the tables are used. As a rule, in the group of tables that store information about employees, the previously described Person and Subdivision have at least one similar record. So, let's take a closer look at Inner Join, an example of which was shown a little earlier.

Example and description of connecting to a single table selection

We have a Person table that stores information about all employees working in the company. Immediately, we note that the main key of this table is the field - Pe_ID. Just on it and the bunch will go.

The second Subdivision table will store information about the departments where employees work. She, in turn, is linked via the Su_Person field to the Person table. What does it say? Based on the data schema, we can say that in the table of departments for each record from the table "Employees" there will be information about the department in which they work. It is for this connection that the Inner Join operator will work.

For a more understandable use, consider the SQL Inner Join operator (examples of its use for one and two tables). If we consider an example for one table, then everything is quite simple:

Select * from Person Inner join Subdivision on Su_Person = Pe_ID

An example of connecting two tables and a subquery

The SQL Inner Join operator, whose use cases for selecting data from several tables can be organized in the above way, works according to a slightly more complicated principle. For two tables, let's complicate the task. Let's say we have a Depart table that stores information about all the departments in each of the divisions. In this table, the number of the department and the number of the employee are recorded, and it is necessary to supplement the data selection with the name of each department. Looking ahead, it is worth saying that two methods can be used to solve this problem.

The first way is to connect the departments table to the selection. In this case, you can organize the query like this:

It is worth noting that such a construction may not always speed up the query. Sometimes there are cases when you have to use an additional data selection in a temporary table (if their volume is too large), and then combine it with the main selection.

An example of using the Inner Join operator for selections from a large number of tables

Building complex queries involves using a significant number of interconnected tables and subqueries to retrieve data. The SQL Inner Join syntax can satisfy these requirements. Examples of using the operator in this case can be complicated not only by selections from many data storage locations, but also from a large number of nested subqueries. For a specific example, you can take a selection of data from system tables (Inner Join SQL statement). Example - 3 tables - in this case will have a rather complex structure.

In this case, three more are connected (to the main table) and several data selection conditions are entered.

When using the Inner Join operator, it is worth remembering that the more complex the query, the longer it will be implemented, so you should look for ways to complete and solve the task faster.

Conclusion

In the end, I would like to say one thing: working with databases is not the most difficult thing in programming, therefore, if desired, absolutely everyone will be able to master the knowledge of building databases, and over time, having gained experience, it will be possible to work with them at a professional level .

Like any two Yin (Water or Earth) signs, two Pisces get along well. Together they will not be bored, the similarity of characters will delight, and not bother them. They are both calm, compliant, sensitive and form a strong couple. Pisces in love are primarily interested in emotions, and partners will give them to each other in abundance.

Pisces-Pisces Compatibility: How to Seduce a Pisces Man?

The Pisces man is sensitive to the violation of his inner peace. He does not like it when unceremonious, active and assertive people break into his world. Pisces woman is the exact opposite of what is described. She is calm and friendly, sociable, but not assertive, cheerful, but does not strive to become the soul of the company. With her, the Pisces man will immediately find a common language. Interestingly, more often Pisces meet not at an art exhibition, in nature, or during dreamy walks around the city, that is, in places traditionally considered “fishy”, but in a completely different setting: at work or in a fun company. Why? Pisces are not "beeches" or gloomy silent people closed in themselves, they love and appreciate the company, but there is always something else behind their fun. It is like ripples in the water, when the reservoir itself hides calm, motionless depths. This duality of the Pisces mood is especially noticeable when they are having fun, working or studying something, that is, doing things in which one cannot be outwardly detached and immersed in oneself. It is this second, deeper layer of their mood that other Pisces will best notice. It is they who will see the features of a fellow zodiac sign, and, seeing their reflection in it, Pisces will definitely reach out to other Pisces. The man and woman of this sign intuitively strive for each other; to conquer the Pisces man, a woman does not need special tricks. Her softness, flexibility, kindness and inner similarity of characters will do everything themselves.

What does an ideal couple look like: Pisces woman - Pisces man?

Two Pisces usually stick together. They are reluctant to go to any events alone. Among friends, they are cheerful, friendly and easy to communicate with. One gets the impression that simultaneously with the general conversation they have a telepathic dialogue with each other - they understand each other so well. Interestingly, Pisces never get bored in any company: if they are not interested in what is happening around them, then they have the best in the world, understanding and loving interlocutor next to them. What else do Pisces get from an alliance with each other, for which reason should they strive for an ideal partnership? In order to answer this question, you need to remember the key word that characterizes Pisces. This word is love. Neither passion, nor profitable union, but sincere, sacrificial and merciful love. Next to each other, Pisces, who managed to overcome obstacles on the way to an ideal union, gain love, tenderness and care. They feel that they are part of the Divine World, filled with love, and therefore they avoid lying, rudeness, and rash acts in their behavior. They have good sexual compatibility and spiritual harmony. The children of this couple grow up in an atmosphere of love and tenderness. It is difficult to say something definite about the financial situation of a pair of Pisces: Pisces are indifferent to money, but this does not exclude their highly paid profession or wealthy (and helping them) relatives.

What are the difficulties in the union of a Pisces woman and a Pisces man?

I would like to say that the difficulties of this couple are obvious and lie in everyday problems, because Pisces are impractical. But, unfortunately, this is not the biggest difficulty of the union. Domestic problems draw attention to themselves, seem to be the main problem, and Pisces rush to solve them without noticing the main thing. Not thriftiness, inability to manage money, isolation from reality - this is all external, lying in the objective areas of life "money", "work", "life". BUT real problem Pisces is hidden in themselves, so it is more difficult to find and fix it. The patron saint of Pisces is Neptune, the planet of illusions. But illusions can also be harmful. What is the source of harmful illusions? In deceit, lies and insincerity. A lie creates an illusion, shows the world not as it is. The second source of harmful illusions is negative meditations. We are talking about any actions that introduce a person into a state of trance, and not about meditation in the narrow sense of the word. An example of negative meditation is sitting for many hours in front of the TV watching TV shows (series “disconnect” a person from reality) or the same hours of talking about nothing with a girlfriend on the phone (this is another zombie action). And finally, chemicals create illusions - alcohol and drugs. All of the above distorts the true understanding of love in Pisces and alienates them from each other. Unfortunately, most Pisces are susceptible to one temptation or another of illusion. Very often they seek refuge in them from scandals caused by domestic turmoil. In order not to lie to each other and not to get confused in the end in one's own deceit, in order not to fence oneself off from the problems of a partner behind "Tanks" and serials, so that there is no temptation to "relax" with alcohol, all these illusions must be opposed by others - constructive ones. Neptune symbolizes deception, but it also symbolizes falling in love (also a kind of “deception”, when falling in love, a person does not see the real features of the object of love). Love each other, constantly warm up this feeling, arrange romantic dates and be gentle with each other. Meditations on series computer games and other harmful in large numbers) contrast things with the creation of an imaginary world for two. Fill it with phrases understandable only to you, your favorite music or memorable corners of nature. As far as alcohol and drugs are concerned, the best thing to remember here is: You can't do that. “Not a table, not half a table” - Pisces has an increased risk of getting involved in such things. Things of a higher order inherent in Neptune will help to resist temptation: love, faith and spirituality.

Compatibility of Pisces Woman and Pisces Man at Work

If you do not take into account that Pisces are people of a not particularly businesslike warehouse, then there is nothing to object to the cooperation of Pisces. They understand each other well, are not aggressive, easily adapt to the situation. And even their tendency to intrigue and "muddy the waters" is not terrible - a man and a woman are not interested in plotting together and "washing the bones" of employees, and in business matters they rarely reach those peaks where intrigues can cause serious damage to the company.

Compatibility of Pisces woman and Pisces man - colleagues or partners

They understand each other well, easily adapt to working together, do not quarrel. If the work does not involve frequent hands-on work, then this business couple will show itself well. But in their own business, both have little leadership qualities, both will prefer to dream rather than realize, so the success of their business is doubtful and happens in some specific areas (for example, in creative unions).

When the Pisces woman is the boss and the Pisces man is the subordinate

The Pisces man can be a good subordinate, but the woman of this sign does not know how to set goals and control employees. Therefore, the efficiency of the work of her subordinates is low, and this is especially true of the Pisces man, who is not distinguished by self-discipline and initiative. On the other hand, he will not "hook up" the boss and rush to her place, like many others who felt her weakness, and therefore they will have a good relationship (though often to the detriment of work).

When the Pisces woman is the subordinate and the Pisces man is the boss

Unlike the Pisces woman, the men of this sign often imitate violent activity, take on global projects, create confusion and turmoil among subordinates. In this case, the Pisces woman fences herself off from what is happening at work and does not participate in the active work of those who have not yet figured out the boss and did not understand that his fuse will not last long.

Pisces Woman and Pisces Man Compatibility in Friendship

Pisces get along well with each other. They are easy and interesting together, they have the same temperament, interests and tastes. Often, Pisces friends eventually begin to consider each other as something like relatives. And given that the love of Pisces is to some extent asexual, they love not only a partner, but also relatives, friends and people in general, then such a pair of outside friends is often confused with a couple in love. They happily spend a lot of time together, do not quarrel and take care of each other. Their "halves" need to be on the alert: the relationship of the two Pisces will easily grow from friendly to romantic.