Rules for Subqueries

Subquery Fundamental

A subquery is a ‘Select’ query placed inside another query or SQL statement. A subquery can be used with a SELECT, INSERT, UPDATE, or DELETE statement and is generally placed within a WHERE, HAVING, or FROM clause of the outer or main query....

Rules for Subqueries

The subquery is generally included after the WHERE clause, HAVING clause or FROM clause of the outer query. Subqueries can also be used in a ‘Select’ statement to get a column value dynamically. Subquery is always nested within a parenthesis ‘()’. Subqueries can be used with another subquery, as nested queries. A subquery must contain the SELECT query and the FROM clause with ‘WHERE’ condition. Subqueries that need to return more than one row should be used with multiple value operators like IN, ALL, ANY or EXISTS. The datatypes like ntext, text, and image columns are not allowed in the select list of subqueries. ORDER BY command can not be used in a subquery except when TOP is used. In a subquery the COMPUTE and INTO clauses can not be used....

Types of Subqueries

There are different types of subqueries used in SQL Server based on usage and data result needed. Let us look into the common types of subqueries in more detail with examples....

Benefits of Using Subqueries in SQL Server

Helps to avoid Code duplication...

Conclusion

Subqueries are a great tool in SQL Server for writing efficient and powerful SQL queries by accessing data from multiple tables and creating dynamic values in a column from a subquery result. Efficient use of subqueries can be very useful in writing effective SQL Queries....