8.3. INNER JOIN
- The SQL INNER JOIN clause matches rows in one table with rows in other tables and allows you to query rows that contain columns from both tables.
- The INNER JOIN clause is an optional part of the SELECT statement. It appears immediately after the FROM clause.
- Before using the INNER JOIN clause, you have to specify the following criteria:
- First, the main table that appears in the FROM clause.
- Second, the table that you want to join with the main table, which appears in the INNER-JOIN clause. In theory, you can join a table with many other tables. However, for a better performance, you should limit the number of tables to join.
- Third, the join condition or join predicate. The join condition appears after the ON keyword of the INNER JOIN clause. The join condition is the rule for matching rows in the main table with the rows in the other tables.
QUERY: - SELECT T1.column_name, T2.column_name FROM table1 T1 INNER JOIN table1 T2 on condition;
EXAMPLE: - SELECT a.e_id, a.f_name, b.salary FROM employee a INNER JOIN salary b on a.e_id = b.e_id;
Last modified: Monday, 2 December 2019, 12:19 PM