From: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
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To: | guenther(at)laokoon(dot)IN-Berlin(dot)DE (Christian Guenther) |
Cc: | pgsql-sql(at)hub(dot)org |
Subject: | Re: [SQL] sum-function |
Date: | 1999-10-23 04:55:35 |
Message-ID: | 799.940654535@sss.pgh.pa.us |
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Lists: | pgsql-sql |
guenther(at)laokoon(dot)IN-Berlin(dot)DE (Christian Guenther) writes:
> udmsearch=> select sum( dict.word = 'mysql') from dict\g
> ERROR: Unable to select an aggregate function sum(bool)
> What does the ERROR mean.
The '=' operator produces a boolean (true/false) result, but
sum() wants a numeric input. Postgres is a strongly-typed
system, so it doesn't think booleans are interchangeable
with numerics.
It's been suggested several times that Postgres should
provide a standard conversion function that converts
boolean values to 0/1 numeric values, but no one's gotten
around to making one. In the meantime you could get the
result that I think you want with something like
select sum(case when dict.word = 'mysql' then 1 else 0 end) ...
regards, tom lane
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