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JOIN a table with a subquery A subquery can be used with JOIN operation. In the example below, the subquery actually returns a temporary table which is handled by database server in memory. The temporary table from the subquery is given an alias so that we can refer to it in the outer select statement. Note that the left and right table of the join keyword must both return a common key that can be used for the join. Also note that, using subquery in JOIN operation should generally be avoided if you can rewrite your query in a different way, the reason being that no indexes can be used on a temporary table in memory. Practice #1: Use subquery in SELECT statement with an aggregate function. Most of the queries in the tutorials need Northwind MySQL database, you can download the database script on this page. /*
Query result set - 8 rows returned: Other tutorials in this category 1. What is subquery |
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