You can use a subquery in a SELECT, INSERT, DELETE, or UPDATE statement to perform the following tasks: Compare an expression to the result of the query. These subqueries can reside in the WHERE clause, the FROM clause, or the SELECT clause. Here is an example of a subquery: SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2); Note that alias must be used to distinguish table names in the SQL query that contains correlated subqueries. The inner query executes first before its parent query so that the results of an inner query can be passed to the outer query. A subquery is known as the inner query, and the query that contains subquery is known as the outer query. There is no general syntax; subqueries are regular queries placed inside parenthesis. A subquery can be used anywhere an expression is allowed. You can create subqueries within your SQL statements. A subquery in MySQL is a query, which is nested into another SQL query and embedded with SELECT, INSERT, UPDATE or DELETE statement along with the various operators. Copy and paste the following SQL to your SQLyog free Community Edition query window. MySQL Subquery. In this part of the MySQL tutorial, we will mention subqueries in MySQL. mysql> select Id,EmployeeName from CountWithSubqueryDemo - > where - > ( - > select count(*) from CountWithSubqueryDemo - > )=2; Empty set (0.03 sec) In the above query we are getting empty set because it returns the row if the table have two records only. It is also called an inner query or a nested query. It is a query expression enclosed in parentheses. Determine if an expression is included in the results of the query. The query optimizer is more mature for joins than for subqueries, so in many cases a statement that uses a subquery should normally be rephrased as a join to gain the extra speed in performance. The subquery can be added to further filter the result set using comparison operators like <,>, =, IN or BETWEEN, etc. A subquery is a SELECT statement within another statement. The SQL subquery syntax. What is a subquery in MySQL? Subqueries can be used in different ways and at different locations inside a query: Here is a subquery with the IN operator. A subquery is a query in a query. In MySQL, the subquery is nested inside WHERE clause of an outer SQL SELECT statement. We can also nest the subquery with another subquery. If we want to get the rows as result from the Database table where a particular value should be present in a list of values available through conditional query then, we use MySQL IN operator. Thus, the MySQL IN operator like other MySQL operators allows comparing a value matching from the set of column values returned by a subquery statement. In MySQL, a subquery is a query within a query. 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