Exists in Sql Server

 Exists

In the previous section, we used IN to link the inner query and the outer query in a subquery statement.IN is not the only way to do so -- one can use many operators such as >, <, or =. EXISTS is a special operator that we will discuss in this section. EXISTS simply tests whether the inner query returns any row. If it does, then the outer query proceeds. If not, the outer query does not execute, and the entire SQL statement returns nothing. The syntax for EXISTS is: SELECT "column_name1" FROM "table_name1" WHERE EXISTS (SELECT * FROM "table_name2" WHERE [Condition]) Please note that instead of *, you can select one or more columns in the inner query. The effect will be identical. Let's use the same example tables: Table Store_Information store_name Sales Date Los Angeles $1500 Jan-05-1999 San Diego $250 Jan-07-1999 Los Angeles $300 Jan-08-1999 Boston $700 Jan-08-1999 Table Geography region_name store_name East Boston East New York West Los Angeles West San Diego and we issue the following SQL query: SELECT SUM(Sales) FROM Store_Information WHERE EXISTS (SELECT * FROM Geography WHERE region_name = 'West') We'll get the following result: SUM(Sales) 2750 At first, this may appear confusing, because the subquery includes the [region_name = 'West'] condition, yet the query summed up stores for all regions. Upon closer inspection, we find that since the subquery returns more than 0 row, the EXISTS condition is true, and the condition placed inside the inner query does not influence how the outer query is run.