Home > Oracle > UNION ALLcommand is also to combine the results of two queries together, and UNION ALLselects all values.

UNION ALLcommand is also to combine the results of two queries together, and UNION ALLselects all values.

The purpose of the SQL UNION ALLcommand is also to combine the results of two queries together. The difference between UNION ALL andUNION is that, while UNION only selects distinct values, UNION ALLselects all values.

The syntax for UNION ALL is as follows:

[SQL Statement 1]
UNION ALL
[SQL Statement 2]

Let’s use the same example as the previous section to illustrate the difference. Assume that we have the following two 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 Internet_Sales

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 at a store as well as all the dates where there is a sale over the internet. To do so, we use the following SQL statement:

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

Nguồn: http://www.1keydata.com/sql/sql-intersect.html

 


Tags:
  1. No comments yet.
  1. No trackbacks yet.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: