MySQL Cookbook

Combining Columns to Construct Composite Values

Problem

You want to display values that are constructed from multiple table columns.

Solution

One way to do this is to use CONCAT( ). You might also want to give the column a nicer name by using an alias.

Discussion

Column values may be combined to produce composite output values. For example, this expression concatenates srcuser and srchost values into email address format:

CONCAT(srcuser,'@',srchost)

Such expressions tend to produce ugly column names, which is yet another reason why column aliases are useful. The following query uses the aliases sender and recipient to name output columns that are constructed by combining usernames and hostnames into email addresses:

mysql> SELECT
    -> DATE_FORMAT(t,'%M %e, %Y') AS date_sent,
    -> CONCAT(srcuser,'@',srchost) AS sender,
    -> CONCAT(dstuser,'@',dsthost) AS recipient,
    -> size FROM mail;
+--------------+---------------+---------------+---------+
| date_sent    | sender        | recipient     | size    |
+--------------+---------------+---------------+---------+
| May 11, 2001 | barb@saturn   | tricia@mars   |   58274 |
| May 12, 2001 | tricia@mars   | gene@venus    |  194925 |
| May 12, 2001 | phil@mars     | phil@saturn   |    1048 |
| May 13, 2001 | barb@saturn   | tricia@venus  |     271 |
...