Just join.me toclose a deal

Persisting entities

   public static void persistEmployees() {
       Task task1 = new Task("Coding", "Denise");
       Task task2 = new Task("Refactoring", "Rose");
       Task task3 = new Task("Designing", "Denise");
       Task task4 = new Task("Documentation", "Mike");
   
       Employee employee1 = Employee.create("Diana", task1, task3);
       Employee employee2 = Employee.create("Mike", task2, task4);
       Employee employee3 = Employee.create("Tim", task3, task4);
       Employee employee4 = Employee.create("Jack");
   
       EntityManager em = entityManagerFactory.createEntityManager();
       em.getTransaction().begin();
       em.persist(employee1);
       em.persist(employee2);
       em.persist(employee3);
       em.persist(employee4);
       em.getTransaction().commit();
       em.close();
       System.out.println("-- Employee persisted --");
       System.out.println(employee1);
       System.out.println(employee2);
       System.out.println(employee3);
       System.out.println(employee4);
   }
-- Employee persisted --
Employee{id=1, name='Diana', tasks=}
Employee{id=4, name='Mike', tasks=}
Employee{id=7, name='Tim', tasks=}
Employee{id=8, name='Jack', tasks=[]}

INNER JOIN Query

   private static void executeQuery() {
       System.out.println("-- executing query --");
       EntityManager em = entityManagerFactory.createEntityManager();
       Query query = em.createQuery("SELECT DISTINCT e FROM Employee e INNER JOIN e.tasks t");
       List resultList = query.getResultList();
       resultList.forEach(System.out::println);
       em.close();
   }
-- executing query --
Employee{id=7, name='Tim', tasks=}
Employee{id=4, name='Mike', tasks=}
Employee{id=1, name='Diana', tasks=}

Above query returns the rows where employee task is not null, or simply matching records in both Employee and Task tables exist. Only ‘Jack’ excluded because he is not assigned any task.

Alternatively, we can write above query as:

SELECT DISTINCT e FROM Employee e WHERE e.tasks IS NOT EMPTY

Note that ‘INNER’ keyword is optional, so our original query can be written as:

SELECT DISTINCT e FROM Employee e JOIN e.tasks t

Also we used two identifiers, ‘e’ for Employee entity and ‘t’ for task entity.

Advanced options

TypeORM provides a lot of built-in operators that can be used to create more complex comparisons:

Not

import {Not} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    title: Not("About #1")
})

will execute following query:

SELECT * FROM "post" WHERE "title" != 'About #1'

LessThan

import {LessThan} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    likes: LessThan(10)
});

will execute following query:

SELECT * FROM "post" WHERE "likes"  10

LessThanOrEqual

import {LessThanOrEqual} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    likes: LessThanOrEqual(10)
});

will execute following query:

SELECT * FROM "post" WHERE "likes"  10

MoreThan

import {MoreThan} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    likes: MoreThan(10)
});

will execute following query:

SELECT * FROM "post" WHERE "likes" > 10

MoreThanOrEqual

import {MoreThanOrEqual} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    likes: MoreThanOrEqual(10)
});

will execute following query:

SELECT * FROM "post" WHERE "likes" >= 10

Equal

import {Equal} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    title: Equal("About #2")
});

will execute following query:

SELECT * FROM "post" WHERE "title" = 'About #2'

Like

import {Like} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    title: Like("%out #%")
});

will execute following query:

SELECT * FROM "post" WHERE "title" LIKE '%out #%'

Between

import {Between} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    likes: Between(1, 10)
});

will execute following query:

SELECT * FROM "post" WHERE "likes" BETWEEN 1 AND 10

In

import {In} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    title: In("About #2", "About #3")
});

will execute following query:

SELECT * FROM "post" WHERE "title" IN ('About #2','About #3')

Any

import {Any} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    title: Any("About #2", "About #3")
});

will execute following query (Postgres notation):

SELECT * FROM "post" WHERE "title" = ANY()

IsNull

import {IsNull} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    title: IsNull()
});

will execute following query:

SELECT * FROM "post" WHERE "title" IS NULL

Raw

import {Raw} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    likes: Raw("dislikes - 4")
});

will execute following query:

SELECT * FROM "post" WHERE "likes" = "dislikes" - 4

In the simplest case, a raw query is inserted immediately after the equal symbol.
But you can also completely rewrite the comparison logic using the function.

import {Raw} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    currentDate: Raw(alias =>`${alias} > NOW()`)
});

will execute following query:

SELECT * FROM "post" WHERE "currentDate" > NOW()

Also you can combine these operators with operator:

import {Not, MoreThan, Equal} from "typeorm";

const loadedPosts = await connection.getRepository(Post).find({
    likes: Not(MoreThan(10)),
    title: Not(Equal("About #2"))
});

will execute following query:

SELECT * FROM "post" WHERE NOT("likes" > 10) AND NOT("title" = 'About #2')

Demo Database

In this tutorial we will use the well-known Northwind sample database.

Below is a selection from the «Orders» table:

OrderID CustomerID EmployeeID OrderDate ShipperID
10308 2 7 1996-09-18 3
10309 37 3 1996-09-19 1
10310 77 8 1996-09-20 2

And a selection from the «Customers» table:

CustomerID CustomerName ContactName Address City PostalCode Country
1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany
2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico
3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico

FULL OUTER JOIN

The command returns all rows
when there is a match in either left table or right table.

The following SQL statement selects all customers, and all orders:

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
FULL OUTER JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;

Note: The keyword returns all the rows from
the left table (Customers), and all the rows from the right table (Orders). If
there are rows in «Customers» that do not have matches in «Orders», or if there
are rows in «Orders» that do not have matches in «Customers», those rows will be
listed as well.

SQL FULL OUTER JOIN Example

The following SQL statement selects all customers, and all orders:

SELECT Customers.CustomerName, Orders.OrderID
FROM Customers
FULL OUTER JOIN Orders
ON Customers.CustomerID=Orders.CustomerID
ORDER BY Customers.CustomerName;

A selection from the result set may look like this:

CustomerName OrderID
Alfreds Futterkiste Null
Ana Trujillo Emparedados y helados 10308
Antonio Moreno Taquería 10365

Note: The FULL OUTER JOIN keyword returns all matching
records from both tables whether the other table matches or not. So, if
there are rows in «Customers» that do not have matches in «Orders», or if there
are rows in «Orders» that do not have matches in «Customers», those rows will be
listed as well.

INNER JOIN with WHERE Clause

public class ExampleMain2 {
  private static EntityManagerFactory entityManagerFactory =
          Persistence.createEntityManagerFactory("example-unit");

  public static void main(String[] args) {
      try {
          persistEmployees();
          executeQuery();
      } finally {
          entityManagerFactory.close();
      }
  }
    .............
  private static void executeQuery() {
      System.out.println("-- executing query --");
      EntityManager em = entityManagerFactory.createEntityManager();
      Query query = em.createQuery(
              "SELECT DISTINCT e FROM Employee e INNER JOIN e.tasks t where t.supervisor='Denise'");
      List resultList = query.getResultList();
      resultList.forEach(System.out::println);
      em.close();
  }
}
-- Employee persisted --Employee{id=1, name='Diana', tasks=}Employee{id=4, name='Mike', tasks=}Employee{id=7, name='Tim', tasks=}Employee{id=8, name='Jack', tasks=[]}-- executing query --Employee{id=7, name='Tim', tasks=}Employee{id=1, name='Diana', tasks=}

Above query returns only those employees who have the tasks supervised by ‘Denise’.

Another JOIN query with WHERE clause:

public class ExampleMain3 {
  private static EntityManagerFactory entityManagerFactory =
          Persistence.createEntityManagerFactory("example-unit");

  public static void main(String[] args) {
      try {
          persistEmployees();
          executeQuery();
      } finally {
          entityManagerFactory.close();
      }
  }
    .............
  private static void executeQuery() {
      System.out.println("-- executing query --");
      EntityManager em = entityManagerFactory.createEntityManager();
      Query query = em.createQuery(
              "SELECT DISTINCT e FROM Employee e INNER JOIN e.tasks t where t.supervisor = e.name");
      List resultList = query.getResultList();
      resultList.forEach(System.out::println);
      em.close();
  }
}
-- Employee persisted --Employee{id=1, name='Diana', tasks=}Employee{id=4, name='Mike', tasks=}Employee{id=7, name='Tim', tasks=}Employee{id=8, name='Jack', tasks=[]}-- executing query --Employee{id=4, name='Mike', tasks=}

Above query selects only ‘Mike’ because he has a task (‘Documentation’) whose supervisor is himself. The task ‘Documentation’ is assigned to two employees ‘Mike’ and ‘Tim’ and ‘Mike’ is the one who is also supervising the ‘Documentation’ team.

Note that a JOIN query can also be made for single valued relationship as well (other than collection based relationship). Check out an example here.

INNER JOIN

The command returns rows that have matching values in both tables.

The following SQL selects all orders with customer information:

Example

SELECT Orders.OrderID, Customers.CustomerNameFROM OrdersINNER JOIN
Customers ON Orders.CustomerID = Customers.CustomerID;

Note: The INNER JOIN keyword selects all rows from both
tables as long as there is a match between the columns. If there are records in the
«Orders» table that do not have matches in «Customers», these orders will not
be shown!

The following SQL statement selects all orders with customer and shipper
information:

Example

SELECT Orders.OrderID, Customers.CustomerName, Shippers.ShipperNameFROM
((OrdersINNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);

Inner Join

An inner join focuses on the commonality between two tables. When using an inner join, there must be at least some matching data between two (or more) tables that are being compared. An inner join searches tables for matching or overlapping data. Upon finding it, the inner join combines and returns the information into one new table.

Example of Inner Join

Let’s consider a common scenario of two tables: product prices and quantities. The common information in the two tables is product name, so that is the logical column to join the tables on. There are some products that are common in the two tables; others are unique to one of the tables and don’t have a match in the other table.

An inner join on Products returns information about only those products that are common in both tables.

INNER JOIN

The command returns rows that have matching values in both tables.

The following SQL selects all orders with customer information:

Example

SELECT Orders.OrderID, Customers.CustomerNameFROM OrdersINNER JOIN
Customers ON Orders.CustomerID = Customers.CustomerID;

Note: The INNER JOIN keyword selects all rows from both
tables as long as there is a match between the columns. If there are records in the
«Orders» table that do not have matches in «Customers», these orders will not
be shown!

The following SQL statement selects all orders with customer and shipper
information:

Example

SELECT Orders.OrderID, Customers.CustomerName, Shippers.ShipperNameFROM
((OrdersINNER JOIN Customers ON Orders.CustomerID = Customers.CustomerID)
INNER JOIN Shippers ON Orders.ShipperID = Shippers.ShipperID);

When to use JinjaSQL

JinjaSQL is not meant to replace your ORM. ORMs like those provided
by SQLAlchemy or Django are great for a variety of use cases, and should
be the default in most cases. But there are a few use cases where
you really need the power of SQL.

Use JinjaSQL for —

  1. Reporting, business intelligence or dashboard like use cases
  2. When you need aggregation/group by
  3. Use cases that require data from multiple tables
  4. Migration scripts & bulk updates that would benefit from macros

In all other use cases, you should reach to your ORM
instead of writing SQL/JinjaSQL.

While JinjaSQL can handle insert/update statements, you are better off
using your ORM to handle such statements. JinjaSQL is mostly meant
for dynamic select statements that an ORM cannot handle as well.

SQL References

SQL Keywords
ADD
ADD CONSTRAINT
ALTER
ALTER COLUMN
ALTER TABLE
ALL
AND
ANY
AS
ASC
BACKUP DATABASE
BETWEEN
CASE
CHECK
COLUMN
CONSTRAINT
CREATE
CREATE DATABASE
CREATE INDEX
CREATE OR REPLACE VIEW
CREATE TABLE
CREATE PROCEDURE
CREATE UNIQUE INDEX
CREATE VIEW
DATABASE
DEFAULT
DELETE
DESC
DISTINCT
DROP
DROP COLUMN
DROP CONSTRAINT
DROP DATABASE
DROP DEFAULT
DROP INDEX
DROP TABLE
DROP VIEW
EXEC
EXISTS
FOREIGN KEY
FROM
FULL OUTER JOIN
GROUP BY
HAVING
IN
INDEX
INNER JOIN
INSERT INTO
INSERT INTO SELECT
IS NULL
IS NOT NULL
JOIN
LEFT JOIN
LIKE
LIMIT
NOT
NOT NULL
OR
ORDER BY
OUTER JOIN
PRIMARY KEY
PROCEDURE
RIGHT JOIN
ROWNUM
SELECT
SELECT DISTINCT
SELECT INTO
SELECT TOP
SET
TABLE
TOP
TRUNCATE TABLE
UNION
UNION ALL
UNIQUE
UPDATE
VALUES
VIEW
WHERE

MySQL Functions
String Functions
ASCII
CHAR_LENGTH
CHARACTER_LENGTH
CONCAT
CONCAT_WS
FIELD
FIND_IN_SET
FORMAT
INSERT
INSTR
LCASE
LEFT
LENGTH
LOCATE
LOWER
LPAD
LTRIM
MID
POSITION
REPEAT
REPLACE
REVERSE
RIGHT
RPAD
RTRIM
SPACE
STRCMP
SUBSTR
SUBSTRING
SUBSTRING_INDEX
TRIM
UCASE
UPPER

Numeric Functions
ABS
ACOS
ASIN
ATAN
ATAN2
AVG
CEIL
CEILING
COS
COT
COUNT
DEGREES
DIV
EXP
FLOOR
GREATEST
LEAST
LN
LOG
LOG10
LOG2
MAX
MIN
MOD
PI
POW
POWER
RADIANS
RAND
ROUND
SIGN
SIN
SQRT
SUM
TAN
TRUNCATE

Date Functions
ADDDATE
ADDTIME
CURDATE
CURRENT_DATE
CURRENT_TIME
CURRENT_TIMESTAMP
CURTIME
DATE
DATEDIFF
DATE_ADD
DATE_FORMAT
DATE_SUB
DAY
DAYNAME
DAYOFMONTH
DAYOFWEEK
DAYOFYEAR
EXTRACT
FROM_DAYS
HOUR
LAST_DAY
LOCALTIME
LOCALTIMESTAMP
MAKEDATE
MAKETIME
MICROSECOND
MINUTE
MONTH
MONTHNAME
NOW
PERIOD_ADD
PERIOD_DIFF
QUARTER
SECOND
SEC_TO_TIME
STR_TO_DATE
SUBDATE
SUBTIME
SYSDATE
TIME
TIME_FORMAT
TIME_TO_SEC
TIMEDIFF
TIMESTAMP
TO_DAYS
WEEK
WEEKDAY
WEEKOFYEAR
YEAR
YEARWEEK

Advanced Functions
BIN
BINARY
CASE
CAST
COALESCE
CONNECTION_ID
CONV
CONVERT
CURRENT_USER
DATABASE
IF
IFNULL
ISNULL
LAST_INSERT_ID
NULLIF
SESSION_USER
SYSTEM_USER
USER
VERSION

SQL Server Functions
String Functions
ASCII
CHAR
CHARINDEX
CONCAT
Concat with +
CONCAT_WS
DATALENGTH
DIFFERENCE
FORMAT
LEFT
LEN
LOWER
LTRIM
NCHAR
PATINDEX
QUOTENAME
REPLACE
REPLICATE
REVERSE
RIGHT
RTRIM
SOUNDEX
SPACE
STR
STUFF
SUBSTRING
TRANSLATE
TRIM
UNICODE
UPPER

Numeric Functions
ABS
ACOS
ASIN
ATAN
ATN2
AVG
CEILING
COUNT
COS
COT
DEGREES
EXP
FLOOR
LOG
LOG10
MAX
MIN
PI
POWER
RADIANS
RAND
ROUND
SIGN
SIN
SQRT
SQUARE
SUM
TAN

Date Functions
CURRENT_TIMESTAMP
DATEADD
DATEDIFF
DATEFROMPARTS
DATENAME
DATEPART
DAY
GETDATE
GETUTCDATE
ISDATE
MONTH
SYSDATETIME
YEAR

Advanced Functions
CAST
COALESCE
CONVERT
CURRENT_USER
IIF
ISNULL
ISNUMERIC
NULLIF
SESSION_USER
SESSIONPROPERTY
SYSTEM_USER
USER_NAME

MS Access Functions
String Functions
Asc
Chr
Concat with &
CurDir
Format
InStr
InstrRev
LCase
Left
Len
LTrim
Mid
Replace
Right
RTrim
Space
Split
Str
StrComp
StrConv
StrReverse
Trim
UCase

Numeric Functions
Abs
Atn
Avg
Cos
Count
Exp
Fix
Format
Int
Max
Min
Randomize
Rnd
Round
Sgn
Sqr
Sum
Val

Date Functions
Date
DateAdd
DateDiff
DatePart
DateSerial
DateValue
Day
Format
Hour
Minute
Month
MonthName
Now
Second
Time
TimeSerial
TimeValue
Weekday
WeekdayName
Year

Other Functions
CurrentUser
Environ
IsDate
IsNull
IsNumeric

SQL OperatorsSQL Data TypesSQL Quick Ref

SQL JOIN Examples

Problem:

SELECT OrderNumber, TotalAmount, FirstName, LastName, City, Country
  FROM  JOIN Customer
    ON .CustomerId = Customer.Id

Results:

OrderNumber TotalAmount FirstName LastName City Country
542378 440.00 Paul Henriot Reims France
542379 1863.40 Karin Josephs Münster Germany
542380 1813.00 Mario Pontes Rio de Janeiro Brazil
542381 670.80 Mary Saveley Lyon France
542382 3730.00 Pascale Cartrain Charleroi Belgium
542383 1444.80 Mario Pontes Rio de Janeiro Brazil
542384 625.20 Yang Wang Bern Switzerland
PRODUCT
Id
ProductName
SupplierId
UnitPrice
Package
IsDiscontinued
ORDERITEM
Id
OrderId
ProductId
UnitPrice
Quantity
ORDER
Id
OrderDate
OrderNumber
CustomerId
TotalAmount

Problem:

SELECT O.OrderNumber, CONVERT(date,O.OrderDate) AS Date, 
       P.ProductName, I.Quantity, I.UnitPrice 
  FROM  O 
  JOIN OrderItem I ON O.Id = I.OrderId 
  JOIN Product P ON P.Id = I.ProductId
ORDER BY O.OrderNumber

Results:

OrderNumber Date ProductName Quantity UnitPrice
542378 7/4/2012 12:00:00 AM Queso Cabrales 12 14.00
542378 7/4/2012 12:00:00 AM Singaporean Hokkien Fried Mee 10 9.80
542378 7/4/2012 12:00:00 AM Mozzarella di Giovanni 5 34.80
542379 7/5/2012 12:00:00 AM Tofu 9 18.60
542379 7/5/2012 12:00:00 AM Manjimup Dried Apples 40 42.40
542380 7/8/2012 12:00:00 AM Jack’s New England Clam Chowder 10 7.70
542380 7/8/2012 12:00:00 AM Manjimup Dried Apples 35 42.40
542380 7/8/2012 12:00:00 AM Louisiana Fiery Hot Pepper Sauce 15 16.80
542381 7/8/2012 12:00:00 AM Gustaf’s Knäckebröd 6 16.80
542381 7/8/2012 12:00:00 AM Ravioli Angelo 15 15.60
542381 7/8/2012 12:00:00 AM Louisiana Fiery Hot Pepper Sauce 20 16.80
542382 7/9/2012 12:00:00 AM Sir Rodney’s Marmalade 40 64.80
542382 7/9/2012 12:00:00 AM Geitost 25 2.00

  Previous

Next  

OUTER JOIN

Последнее обновление: 20.07.2017

В предыдущей теме было рассмотрено внутреннее соединение таблиц. Но MS SQL Server также поддерживает внешнее соединение или outer join.
В отличие от inner join внешнее соединение возвращает все строки одной или двух таблиц, которые участвуют в соединении.

Outer Join имеет следующий формальный синтаксис:

SELECT столбцы
FROM таблица1
	{LEFT|RIGHT|FULL}  JOIN таблица2 ON условие1
	 JOIN таблица3 ON условие2]...

Перед оператором JOIN указывается одно из ключевых слов LEFT,
RIGHT или FULL, которые определяют тип соединения:

  • LEFT: выборка будет содержать все строки из первой или левой таблицы

  • RIGHT: выборка будет содержать все строки из второй или правой таблицы

  • FULL: выборка будет содержать все строки из обоих таблиц

Также перед оператором JOIN может указываться ключевое слово OUTER, но его применение необязательно.
Далее после JOIN указывается присоединяемая таблица, а затем идет условие соединения.

Например, соединим таблицы Orders и Customers:

SELECT FirstName, CreatedAt, ProductCount, Price, ProductId 
FROM Orders LEFT JOIN Customers 
ON Orders.CustomerId = Customers.Id

Таблица Orders является первой или левой таблицей, а таблица Customers — правой таблицей. Поэтому, так как здесь используется
выборка по левой таблице, то вначале будут выбираться все строки из Orders, а затем к ним по условию будут
добавляться связанные строки из Customers.

По вышеприведенному результату может показаться, что левостороннее соединение аналогично INNER Join, но это не так.
Inner Join объединяет строки из дух таблиц при соответствии условию. Если одна из таблиц содержит строки, которые не соответствуют этому условию, то данные строки
не включаются в выходную выборку. Left Join выбирает все строки первой таблицы и затем присоединяет к ним строки правой таблицы. К примеру, возьмем таблицу Customers и добавим к покупателям информацию об их заказах:

-- INNER JOIN
SELECT FirstName, CreatedAt, ProductCount, Price 
FROM Customers JOIN Orders 
ON Orders.CustomerId = Customers.Id

--LEFT JOIN
SELECT FirstName, CreatedAt, ProductCount, Price 
FROM Customers LEFT JOIN Orders 
ON Orders.CustomerId = Customers.Id

Изменим в примере выше тип соединения на правостороннее:

SELECT FirstName, CreatedAt, ProductCount, Price, ProductId 
FROM Orders RIGHT JOIN Customers 
ON Orders.CustomerId = Customers.Id

Теперь будут выбираться все строки из Customers, а к ним уже будет присоединяться связанные по условию строки из таблицы Orders:

Поскольку один из покупателей из таблицы Customers не имеет связанных заказов из Orders, то соответствующие столбцы, которые берутся из Orders,
будут иметь значение NULL.

Используем левостороннее соединение для добавления к заказам информации о пользователях и товарах:

SELECT Customers.FirstName, Orders.CreatedAt, 
       Products.ProductName, Products.Manufacturer
FROM Orders 
LEFT JOIN Customers ON Orders.CustomerId = Customers.Id
LEFT JOIN Products ON Orders.ProductId = Products.Id

И также можно применять более комплексные условия с фильтрацией и сортировкой. Например, выберем все заказы с информацией о клиентах и товарах по тем товарам,
у которых цена меньше 45000, и отсортируем по дате заказа:

SELECT Customers.FirstName, Orders.CreatedAt, 
       Products.ProductName, Products.Manufacturer
FROM Orders 
LEFT JOIN Customers ON Orders.CustomerId = Customers.Id
LEFT JOIN Products ON Orders.ProductId = Products.Id
WHERE Products.Price 

Или выберем всех пользователей из Customers, у которых нет заказов в таблице Orders:

SELECT FirstName FROM Customers
LEFT JOIN Orders ON Customers.Id = Orders.CustomerId
WHERE Orders.CustomerId IS NULL

Также можно комбинировать Inner Join и Outer Join:

SELECT Customers.FirstName, Orders.CreatedAt, 
       Products.ProductName, Products.Manufacturer
FROM Orders 
JOIN Products ON Orders.ProductId = Products.Id AND Products.Price 

Вначале по условию к таблице Orders через Inner Join присоединяется связанная информация из Products, затем через Outer Join
добавляется информация из таблицы Customers.

Cross Join

Cross Join или перекрестное соединение создает набор строк, где каждая строка из одной таблицы соединяется с каждой строкой из второй таблицы.
Например, соединим таблицу заказов Orders и таблицу покупателей Customers:

SELECT * FROM Orders CROSS JOIN Customers

Если в таблице Orders 3 строки, а в таблице Customers то же три строки, то в результате перекрестного соединения создается 3 * 3 = 9 строк вне зависимости,
связаны ли данные строки или нет.

При неявном перекрестном соединении можно опустить оператор CROSS JOIN и просто перечислить все получаемые таблицы:

SELECT * FROM Orders, Customers

НазадВперед

Полное множество

MySQL не знает соединения FULL OUTER JOIN. Что если нужно получить полное множество?

Первый способ — объединение запросов LEFT и RIGHT.

(SELECT p.id, p.name `Имя сотрудника`, ps.id `pos.id`, ps.name `Должность`
FROM `persons` p
LEFT OUTER JOIN `positions` ps ON ps.id = p.post_id)
UNION
(SELECT p.id, p.name `Имя сотрудника`, ps.id `pos.id`, ps.name `Должность`
FROM `persons` p
RIGHT OUTER JOIN `positions` ps ON ps.id = p.post_id)

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(SELECTp.id,p.name`Имясотрудника`,ps.id`pos.id`,ps.name`Должность`

FROM`persons`p

LEFT OUTER JOIN`positions`ps ON ps.id=p.post_id)

UNION

(SELECTp.id,p.name`Имясотрудника`,ps.id`pos.id`,ps.name`Должность`

FROM`persons`p

RIGHT OUTER JOIN`positions`ps ON ps.id=p.post_id)

При таком вызове UNION, после слияния результатов, SQL отсечет дубли (как DISTINCT). Для отсечения дублей SQL прибегает к сортировке. Это может сказываться на быстродействии.

Второй способ — объединение LEFT и RIGHT, но в одном из запросов мы исключаем часть, соответствующую INNER. А объединение задаём как UNION ALL, что позволяет движку SQL обойтись без сортировки.

(SELECT p.id, p.name `Имя сотрудника`, ps.id `pos.id`, ps.name `Должность`
FROM `persons` p
LEFT OUTER JOIN `positions` ps ON ps.id = p.post_id)
UNION ALL
(SELECT p.id, p.name `Имя сотрудника`, ps.id `pos.id`, ps.name `Должность`
FROM `persons` p
RIGHT OUTER JOIN `positions` ps ON ps.id = p.post_id
WHERE p.id IS NULL)

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(SELECTp.id,p.name`Имясотрудника`,ps.id`pos.id`,ps.name`Должность`

FROM`persons`p

LEFT OUTER JOIN`positions`ps ON ps.id=p.post_id)

UNION ALL

(SELECTp.id,p.name`Имясотрудника`,ps.id`pos.id`,ps.name`Должность`

FROM`persons`p

RIGHT OUTER JOIN`positions`ps ON ps.id=p.post_id

WHEREp.id ISNULL)

Этот пример показывает нам как исключить пересечение и получить только левую или правую часть множества.

Basic Usage

First, import the class and create an object. is thread-safe, so you can safely create one object at startup and use it everywhere.

from jinjasql import JinjaSql
j = JinjaSql()

Next, create your template query. You can use the full power of Jinja templates over here — macros, includes, imports, if/else conditions, loops, filters and so on. You can load the template from a file or from database or wherever else Jinja supports.

template = """
    SELECT project, timesheet, hours
    FROM timesheet
    WHERE user_id = {{ user_id }}
    {% if project_id %}
    AND project_id = {{ project_id }}
    {% endif %}
"""

Create a context object. This object is a regular dictionary, and can contain nested dictionaries, lists or objects. The template query is evaluated against this context object.

data = {
    "project_id": 123,
    "user_id": u"sripathi"
}

Finally, call the method with the template and the context. You get back two things:

  1. is the generated SQL query. Variables are replaced by %s
  2. is an array of parameters corresponding to the %s
query, bind_params = j.prepare_query(template, data)

This is the query that is generated:

expected_query = """
    SELECT project, timesheet, hours
    FROM timesheet
    WHERE user_id = %s

    AND project_id = %s
"""

And these are the bind parameters:

self.assertEquals(bind_params, )
self.assertEquals(query.strip(), expected_query.strip())

You can now use the query and bind parameters to execute the query. For example, in django, you would do something like this:

from django.db import connection
with connection.cursor() as cursor:
    cursor.execute(query, bind_params)
    for row in cursor.fetchall():
        # do something with the results
        pass

Внешнее соединение

Внешнее соединение (outer join) применяется для возврата всех строк, которые удовлетворяют указанному условию соединения, плюс некоторых или всех строк из таблицы, в которой нет подходящих строк, удовлетворяющих указанному условию соединения. Существуют три вида внешнего соединения: левое внешнее соединение (left outer join), правое внешнее соединение (right outer join) и полное внешнее соединение (full outer join). В операторе полного внешнего соединения слово обычно опускается.

Oracle позволяет использовать операцию внешнего соединения, подразумевающую применение знака плюс (+) для обозначения недостающих значений в одной таблице, но рекомендует лучше использовать вместо нее более новый синтаксис соединения ISO/ANSI. Ниже приведен пример типичного запроса с оператором полного внешнего соединения: 

SQL> SELECT DISTINCT NVL(dept_name, 'No Dept') deptname,
COUNT(empno) nbr_emps
FROM emp FULL JOIN dept
ON dept.deptno = emp.deptno
GROUP BY dname;

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