Subqueries in SQL Server – SQL Server Tutorial

SUB QUERIES   :–

• A query embeded in another query is called “sub querry”.
• In this ,there will be two queries,one queries called inner-query and another query is called outer query.
• When it is executed,first inner query is executed then outer query
• The result of inner query act as input to outer query.

Types of sub queries  :-

1. standard sub queries [follows where clause]
2. derived tables [follows from clause]
3. scalar subqueries [follows select clause]

 Standard sub queries  :–

• Subqueries follows where clause (or) standard subquries.
• Outer query can be  insert, Update, Delete, Select
• Inner query must be always select.

Syntax :–   Select   <collist> from <tabname> where colname operation[select statement]

• Use subqueries when where clause is based on unknown condition.

Types  of standard subqueries  :-

1. Single row subquery
2. multi row subquery
3. nested queries
4. co-related subqueries