Using an Alias in SQL Calculations
Solution 1
Simply wrap your reused alias with (SELECT alias)
:
SELECT 10 AS my_num,
(SELECT my_num) * 5 AS another_number
FROM table
Solution 2
You'll need to use a subselect to use that aliases that way
SELECT my_num*5 AS another_number FROM
(
SELECT 10 AS my_num FROM table
) x
Solution 3
Aliases in sql are not like variables in a programming language. Aliases can only be referenced again at certain points (particularly in GROUP BY
and HAVING
clauses). But you can't reuse an alias in the SELECT
clause. So you can use a derived query (such as suggested by Rubens Farias) which lets you basically rename your columns and/or name any computed columns.
Or you could use a VIEW
if your formulas are generally fixed
CREATE VIEW table10 AS SELECT 10 AS my_num FROM table;
SELECT my_num * 5 AS another_number FROM table10;
I believe that will be slightly faster than using a derived query but it probably depends a lot on your real query.
Or you could just duplicate the work:
SELECT 10 AS my_num, 10 * 5 AS another_number FROM table;
Which might be convenient in something like php/perl:
my $my_num = 10;
my $query = "SELECT $my_num AS my_num, $my_num * 5 AS another_number FROM table";
Tom Rossi
Updated on July 11, 2022Comments
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Tom Rossi almost 2 years
Why won't this query work?
SELECT 10 AS my_num, my_num*5 AS another_number FROM table
In this example, I'm trying to use the my_num alias in other calculations. This results in unknown column "my_num"
This is a simplified version of what I am trying to do, but basically I would like to use an alias to make other calculations. My calculations are much more complicated and thats why it would be nice to alias it since I repeat it several times different ways.
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Rubens Farias almost 11 years@RyanHeneise, it's a subselect alias; that way you could go with
x.my_num
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Carlos Gant almost 10 yearsI am wondering where that functionality is documented. I've searched in the whole MySQL documentation and I have not found it. I don't know how this "alias reusing" works and I am curious about portability or performance impact. If someone knows more about this I will appreciate a link. Thanks you.
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Eaten by a Grue about 8 yearsthis just made my week.. maybe month. super useful especially with aliases built from flow control statements like
IF()
,CASE()
, etc -
DCoder almost 8 years@CarlosGant: The
(SELECT alias)
part is treated as a "dependent subquery", at least according to MySQL'sEXPLAIN
and Visual Explain functions. -
Pang over 7 yearsNote that
CROSS APPLY
does not appear to be available in MySQL (yet). -
Captain Hypertext about 7 yearsNevermind, it didn't work for me. I got "unknown column".
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Ray Coder about 3 years
SELECT kabupaten.nama AS kabupaten, kecamatan.nama AS kecamatan, SUM(pihaks.luas) AS target_luas, SUM(realisasi.luas) AS realisasi_luas, SELECT(realisasi_luas)/SELECT(target_luas)*100 AS persentase_luas
. Tried like this but not working -
Aaron Franke almost 3 yearsThis doesn't work for me if I try to use
SELECT
multiple times.SELECT Users.Id, SUM(Posts.Score) AS ScoreSum, SUM(Posts.ViewCount) AS ViewSum, (SELECT(ViewSum) / SELECT(ScoreSum)) AS ViewScoreRatio
says "Incorrect syntax near SELECT" for the secondSELECT
.