About SubQueries

Question

What are SubQueries? Why we need of Subquery? which is useful subqueries or Join?

Francis · Answer

What are SubQueries? SQL Server 2008 SQL Server 2005 A subquery is a query that is nested inside a SELECT, INSERT, UPDATE, or DELETE statement, or inside another subquery. A subquery can be used anywhere an expression is allowed. Why we need of Subquery? Subquery often is an alternative for joins. Also you can use both in your queries. Whenever you hate joins, you can go with Subquery. Since in some places (based on the data on the table) subquery performs "better" than joins.AFAIK, this the one case we need subquery. which is useful subqueries or Join? It is based on the data on hand. In my experience, i found that in some places Subqueries are works better than joins. In some place vice-versa. So it purely depends on your data. Here is some useful links for this debate: https://support.sas.com/documentation/cdl/en/sqlproc/62086/HTML/default/viewer.htm#a001361223.htm http://stackoverflow.com/questions/4799820/when-to-use-sql-sub-queries-versus-a-standard-join Hope this helps!

Raja T · Answer

Hello Gaurav, 1st and 2nd Question Ans subquery is a query within a query. You can create subqueries within your SQL statements. These subqueries can reside in the WHERE clause, the FROM clause, or the SELECT clause. NOTE In SQL Server (Transact-SQL), a subquery is also called an INNER QUERY or INNER SELECT. In SQL Server (Transact-SQL), the main query that contains the subquery is also called the OUTER QUERY or OUTER SELECT. More details check below links http://www.techonthenet.com/sql_server/subqueries.php https://www.simple-talk.com/sql/sql-training/subqueries-in-sql-server/ http://beginner-sql-tutorial.com/sql-subquery.htm 3rd Question Ans Joins and subqueries are both used to combine data from different tables into a single result. They share many similarities and differences. more details refer below links http://www.essentialsql.com/what-is-the-difference-between-a-join-and-subquery/ http://www.exacthelp.com/2012/10/subquery-vs-inner-join-which-one-is.html http://blog.sqlauthority.com/2010/06/06/sql-server-subquery-or-join-various-options-sql-server-engine-knows-the-best/

Ranjit Powar · Answer

http://www.tutorialspoint.com/sql/sql-sub-queries.htm https://technet.microsoft.com/en-us/library/ms189575(v=sql.105).aspx