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This article shows you the use of inner join in the database, the code is concise and easy to understand, it can definitely brighten your eyes. I hope you can get something through the detailed introduction of this article.

INNER JOIN is when the keyword returns a row when there is at least one match in the table. Specific usage: [select column_list from T1 inner join T2 on join_condition].

Inner join (equivalent connection)

The INNER JOIN clause is used to match rows in one table with rows in other tables, and allows you to query row records that contain columns from two tables and return rows with equal join fields in two tables.

Before you can use the INNER JOIN clause, you must specify the following conditions:

First, specify the main table in the FROM clause

Second, the primary table to join in the table should appear in the INNER JOIN clause. In theory, you can join multiple other tables. However, for better performance, you should limit the number of tables to join (preferably no more than three tables)

Finally, join conditions or join predicates. The join condition appears after the ON keyword of the INNER JOIN clause. A join condition is a rule that matches rows in the main table with rows in other tables.

For example:

Suppose you use the INNER JOIN clause to join two tables, T1 and T2, with the following syntax:

SELECT column_listFROM t1INNER JOIN t2 ON join_condition

For each row in the T1 table, the INNER JOIN clause compares it to each row in the T2 table to see if they all meet the join conditions. When the join condition is met, INNER JOIN returns a new row consisting of columns in the T1 and T2 tables.

Note that the rows in the T1 and T2 tables must be matched according to the join conditions. If no match is found, the query returns an empty result set. This logic also applies when more than 2 tables are joined.

The above is the use of inner join in the database. Have you learned any knowledge or skills? If you want to learn more skills or enrich your knowledge reserve, you are welcome to follow the industry information channel.

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