SQL UNION

SQL > Advanced SQL > UnionThe purpose of the SQL UNION query is to combine the results of two queries together. In this respect, UNION is somewhat similar to JOIN in that they are both used to related information from multiple tables. One restriction of UNION is that all corresponding columns need to be of the same data type. Also, when using UNION, only distinct values are selected (similar toSELECT DISTINCT). The syntax is as follows: [SQL Statement 1] UNION [SQL Statement 2]; Say we have the following two tables, Table Store_Information Store_Name Sales Txn_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 Internet_Sales Txn_Date Sales Jan-07-1999 250 Jan-10-1999 535 Jan-11-1999 320 Jan-12-1999 750 and we want to find out all the dates where there is a sales transaction. To do so, we use the following SQL statement: SELECT Txn_Date FROM Store_Information UNION SELECT Txn_Date FROM Internet_Sales; Result: Txn_Date Jan-05-1999 Jan-07-1999 Jan-08-1999 Jan-10-1999 Jan-11-1999 Jan-12-1999 Please note that if we type "SELECT DISTINCT Txn_Date" for either or both of the SQL statement, we will get the same result set.