Subqueries in SQL Server

Subqueries in SQL Server

Sub queries in SQL Server Part - 12

In this post I will explain all about Subqueries in SQL Server. So let’s start.

Subqueries in SQL Server

WHAT IS SUBQUERIES IN SQL SERVER?

A sub-query is a normal T-SQL query that is nested inside another query – using parentheses – created when we have a SELECT statement that serves as the basis for either the condition in another query or part of the data.

  1. Single Row Sub-query: =, >, <, >=, <=, <> etc
  2. Multiple Row Sub-query: in, any/sum, all etc

Nested Sub- Query

A nested sub-query is one that goes only one direction – returns either a single value for use in the outer query or perhaps a list of values to be used with IN operator.

Syntax:

Sub queries in SQL Server Part - 12 - Nested Sub Query
Sub queries in SQL Server Part - 12 - Nested

Correlated Sub- Query

Correlated sub-queries are one of those things that make the impossible to possible. They often turn several lines of code into one and often create a corresponding increase in performance.

Syntax:

Sub queries in SQL Server Part - 12 - correlated

Correlated Sub-queries in the select List

Syntax:

Sub queries in SQL Server Part - 12 - correlated
Sub queries in SQL Server Part - 12 - correlated
Sub queries in SQL Server Part - 12 - correlated
Sub queries in SQL Server Part - 12 - Correlated

EXISTS Operator

The EXISTS operator is used to test for the existence of any record in a sub-query. The EXISTS operator returns true if the subquery returns one or more records.

Syntax:

Sub queries in SQL Server Part - 12 - Exists Operator

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