ProblemYou often retrieve values that are calculated from expressions and you want a simpler way to refer to those values than writing the expressions each time you need them. SolutionUse a view defined such that its columns perform the desired calculations. DiscussionIn Section 3.5, we retrieved several values from the mail table, using expressions to calculate most of them: 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, 2006 | barb@saturn | tricia@mars | 58274 | | May 12, 2006 | tricia@mars | gene@venus | 194925 | | May 12, 2006 | phil@mars | phil@saturn | 1048 | | May 13, 2006 | barb@saturn | tricia@venus | 271 | ... One problem with such a statement is that if you have to issue it often, it's inconvenient to write the expressions repeatedly. You can make the statement results easier to access by using a view. A view is a virtual table that does not contain any data itself. Instead, it's defined as the SELECT statement that retrieves the data of interest. The following view, mail_view, is equivalent to the SELECT statement just shown: mysql> CREATE VIEW mail_view AS -> SELECT -> DATE_FORMAT(t,'%M %e, %Y') AS date_sent, -> CONCAT(srcuser,'@',srchost) AS sender, -> CONCAT(dstuser,'@',dsthost) AS recipient, -> size FROM mail; To access the view contents, refer to it like any other table. You can select some or all of its columns, add a WHERE clause to restrict which rows to retrieve, use ORDER BY to sort the rows, and so forth. For example: mysql> SELECT date_sent, sender, size FROM mail_view -> WHERE size > 100000 ORDER BY size; +--------------+---------------+---------+ | date_sent | sender | size | +--------------+---------------+---------+ | May 12, 2006 | tricia@mars | 194925 | | May 15, 2006 | gene@mars | 998532 | | May 14, 2006 | tricia@saturn | 2394482 | +--------------+---------------+---------+ |