SQL Subquery
Transcript
SQL Subquery
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What is SQL Sqbquery?
A subquery is a SQL query nested inside a larger query.
Where Subquery Occurs?
A subquery may occur in -
- A SELECT clause
- A FROM clause
- A WHERE clause
- The subquery can be nested inside a SELECT,INSERT,UPDATE,or DELETE statement or inside another subquery.
- A subquery is usually added within the WHERE Clause of another SQL SELECT statement.
- You can use the comparison operators, such as >, <, or =.
Subquery Syntax
- The subquery (inner query) executes before the main query (outer query).
- The result of the subquery is used by the main query.
Type of Subqueries
- Single row subquery : Returns zero or one row.
- Multiple row subquery : Returns one or more rows.
- Multiple column subquery : Returns one or more columns.
- Correlated subqueries : Reference one or more columns in the outer SQL statement.
- Nested subqueries : Subqueries are placed within another subqueries.