SQL join a table to itself
Join a table to itself
A SELF JOIN is another type of join in SQL which is used to join a table to itself, especially when the table has a FOREIGN KEY which references its own PRIMARY KEY.
In this join, the participating table appears twice after the FROM clause and is followed by aliases for the tables that qualify column names in the join condition
In this join, those rows are returned from the table which are satisfying the conditions.
Example:
Sample table: company
To get 'company_name' and 'company_city' from 'company' table which is entitled as alias 'a' and 'company_name' form 'company' table which is entitled as alias 'b' after an SELF JOINING with a table itself, the following SQL statement can be used:
SQL Code:
SELECT a.company_name,b.company_name,a.company_city
FROM company a, company b
WHERE a.company_city=b.company_city;
Output:
COMPANY_NAME COMPANY_NAME COMPANY_CITY ------------------------- ------------------------- ------------- Order All Order All Boston Foodies. Jack Hill Ltd London Jack Hill Ltd Jack Hill Ltd London Akas Foods Akas Foods Delhi Foodies. Foodies. London Jack Hill Ltd Foodies. London sip-n-Bite. sip-n-Bite. New York
Explanation:
This is a note for the example:
'a' and 'b' are aliases for the table 'company'.
the a.company_city=b.company_city excludes all pairs containing companies of different cities.
Here is a new document which is a collection of questions with short and simple answers, useful for learning SQL as well as for interviews.
Practice SQL Exercises
- SQL Exercises, Practice, Solution
- SQL Retrieve data from tables [33 Exercises]
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- SQL JOINS
- SQL SUBQUERIES
- SQL Union[9 Exercises]
- SQL View[16 Exercises]
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- Movie Database
- BASIC queries on movie Database [10 Exercises]
- SUBQUERIES on movie Database [16 Exercises]
- JOINS on movie Database [24 Exercises]
- Soccer Database
- Introduction
- BASIC queries on soccer Database [29 Exercises]
- SUBQUERIES on soccer Database [33 Exercises]
- Hospital Database
- Employee Database
- More to come!
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Next: SQL SELF JOIN
SQL: Tips of the Day
SQL Server SELECT into existing table.
INSERT INTO dbo.TABLETWO SELECT col1, col2 FROM dbo.TABLEONE WHERE col3 LIKE @search_key
This assumes there's only two columns in dbo.TABLETWO - you need to specify the columns otherwise:
INSERT INTO dbo.TABLETWO (col1, col2) SELECT col1, col2 FROM dbo.TABLEONE WHERE col3 LIKE @search_key
Database: SQL Server
Ref: https://bit.ly/3y6tpA3
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