UNIONALL

Question

Hi, In sql what is the difference between UNION and UNIONALL? thanks

Satyapriya Nayak · Answer

Hi Arjun, 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 to SELECT DISTINCT). Ex:- 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 Internet_Sales Date Sales Jan-07-1999 $250 Jan-10-1999 $535 Jan-11-1999 $320 Jan-12-1999 $750 SELECT Date FROM Store_Information UNION SELECT Date FROM Internet_Sales Result: Date Jan-05-1999 Jan-07-1999 Jan-08-1999 Jan-10-1999 Jan-11-1999 Jan-12-1999 UNION ALL command is also to combine the results of two queries together. The difference between UNION ALL and UNION is that, while UNION only selects distinct values, UNION ALL selects all values. Ex:- 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 Internet_Sales Date Sales Jan-07-1999 $250 Jan-10-1999 $535 Jan-11-1999 $320 Jan-12-1999 $750 SELECT Date FROM Store_Information UNION ALL SELECT Date FROM Internet_Sales Result: Date Jan-05-1999 Jan-07-1999 Jan-08-1999 Jan-08-1999 Jan-07-1999 Jan-10-1999 Jan-11-1999 Jan-12-1999 Thanks

Vulpes · Answer

UNION combines the rows returned by several queries into a single result set but excludes duplicate rows. UNION ALL does the same as UNION but includes duplicate rows.