October 2002
Intermediate to advanced
1024 pages
27h 26m
English
You want to display values that are constructed from multiple table columns.
One way to do this is to use CONCAT( ). You
might also want to give the column a nicer name by using an alias.
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 | ...