Selecting Data from Tables - MySQL - page 109

CREATE TABLE or ALTER TABLE statement to output columns, but if these defaults are not
suitable, you can use column aliases to specify your own names.
This section explains aliases and shows how to use them to assign column names in
statements. If you're writing a program that must determine the names, see Recipe 10.2
for information about accessing column metadata.
If an output column comes directly from a table, MySQL uses the table column name
for the output column name. The following statement selects four table columns, the
names of which become the corresponding output column names:
mysql> SELECT t, srcuser, srchost, size FROM mail;
+---------------------+---------+---------+---------+
| t | srcuser | srchost | size |
+---------------------+---------+---------+---------+
| 2014-05-11 10:15:08 | barb | saturn | 58274 |
| 2014-05-12 12:48:13 | tricia | mars | 194925 |
| 2014-05-12 15:02:49 | phil | mars | 1048 |
| 2014-05-12 18:59:18 | barb | saturn | 271 |
…
If you generate a column by evaluating an expression, the expression itself is the column
name. This can produce long and unwieldy names in result sets, as illustrated by the
following statement that uses one expression to reformat the dates in the t column, and
another to combine srcuser and srchost into email address format:
mysql> SELECT
-> DATE_FORMAT(t,'%M %e, %Y'), CONCAT(srcuser,'@',srchost), size
-> FROM mail;
+----------------------------+-----------------------------+---------+
| DATE_FORMAT(t,'%M %e, %Y') | CONCAT(srcuser,'@',srchost) | size |
+----------------------------+-----------------------------+---------+
| May 11, 2014 | barb@saturn | 58274 |
| May 12, 2014 | tricia@mars | 194925 |
| May 12, 2014 | phil@mars | 1048 |
| May 12, 2014 | barb@saturn | 271 |
…
To choose your own output column name, use an AS name clause to specify a column
alias (the keyword AS is optional). The following statement retrieves the same result as
the previous one, but renames the first column to date_sent and the second to sender :
mysql> SELECT
-> DATE_FORMAT(t,'%M %e, %Y') AS date_sent,
-> CONCAT(srcuser,'@',srchost) AS sender,
-> size FROM mail;
+--------------+---------------+---------+
| date_sent | sender | size |
+--------------+---------------+---------+
| May 11, 2014 | barb@saturn | 58274 |
| May 12, 2014 | tricia@mars | 194925 |
| May 12, 2014 | phil@mars | 1048 |