Sub-Queries
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A subquery is a SELECT statement embedded within another SQL statement, usually in the WHERE clause. Subqueries allow data to be returned from multiple tables in an alternate way. They can be used with SELECT, INSERT, UPDATE, and DELETE statements along with comparison operators. Subqueries execute first before the main query uses their results. There are two types: single-row subqueries return one row while multiple-row subqueries return more than one row.
Sub-Queries
- 1. SQL SUBQUERY S.M. TOWHIDUL ISLAM 181-35-2435 E
- 2. WHAT IS A SUBQUERY? A subquery is a SELECT statement embedded in a clause of another SQL statement (SELECT, INSERT, UPDATE, DELETE). SQL subquery is usually added in the WHERE Clause of the SQL statement. SELECT . . . FROM . . . WHERE . . . (SELECT . . . FROM . . . WHERE . . .) Main Query Subquery
- 3. SUBQUERY Subquery or Inner query or Nested query. An alternate way of returning data from multiple tables. Subqueries can be used with the following SQL statements along with the comparison operators like =, <, >, >=, <= etc. Subqueries can also be used inside the WHERE or HAVING clause. SELECT select_list From table WHERE OOP operator SELECT select_list From table
- 4. SUB-QUERY SYNTAX The subquery (inner query) executes once before the main query. The result of the subquery is used by the main query (outer query).
- 6. TYPES OF SUBQUERIES Single-row subqueries: Queries that return only one row from the inner SELECT statement.
- 7. TYPES OF SUBQUERIES Multiple-row subqueries: Queries that return more than one row from the inner SELECT statement.
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