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* Question about WHERE CASE
@ 2019-09-05 11:04 Mike Martin <redtux1@gmail.com>
2019-09-05 11:42 ` Re: Question about WHERE CASE Martin Stöcker <martin.stoecker@stb-datenservice.de>
2019-09-05 13:46 ` Re: Question about WHERE CASE Tom Lane <tgl@sss.pgh.pa.us>
0 siblings, 2 replies; 3+ messages in thread
From: Mike Martin @ 2019-09-05 11:04 UTC (permalink / raw)
To: pgsql-sql@lists.postgresql.org
I have come across the following construct which works in postgres
WHERE CASE WHEN $1=dir THEN TRUE ELSE metadir=$1 END
via (
https://stackoverflow.com/questions/49859153/filter-with-yes-no-and-all-in-postgres
)
case when ('yes'= lower($1)) then (phone_number is not null)
when ('no'=lower($1)) then (phone_number is null)
else true end
I was always under the impression that a case expression could only be
on the right side of a where expression ie:
WHERE fieldname=<cse expression>
Is this a postgres extention, cant find any documentation on this
thanks
Mike
^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Question about WHERE CASE
2019-09-05 11:04 Question about WHERE CASE Mike Martin <redtux1@gmail.com>
@ 2019-09-05 11:42 ` Martin Stöcker <martin.stoecker@stb-datenservice.de>
1 sibling, 0 replies; 3+ messages in thread
From: Martin Stöcker @ 2019-09-05 11:42 UTC (permalink / raw)
To: pgsql-sql@lists.postgresql.org
Hi,
where requires a boolean expression, for instance
select * from stuff where true;
Hence "CASE WHEN $1=dir THEN TRUE ELSE metadir=$1 END" returns a boolean
value everything is fine.
Regards martin
Am 05.09.2019 um 13:04 schrieb Mike Martin:
> I have come across the following construct which works in postgres
>
> WHERE CASE WHEN $1=dir THEN TRUE ELSE metadir=$1 END
>
> via
> (https://stackoverflow.com/questions/49859153/filter-with-yes-no-and-all-in-postgres)
> |casewhen('yes'=lower($1))then(phone_number
> isnotnull)when('no'=lower($1))then(phone_number isnull)elsetrue end |
> |I was always under the impression that a case expression could only
> be on the right side of a where expression ie: |
> |WHERE fieldname=<cse expression> |
> |Is this a postgres extention, cant find any documentation on this |
> |thanks |
> |Mike |
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^ permalink raw reply [nested|flat] 3+ messages in thread
* Re: Question about WHERE CASE
2019-09-05 11:04 Question about WHERE CASE Mike Martin <redtux1@gmail.com>
@ 2019-09-05 13:46 ` Tom Lane <tgl@sss.pgh.pa.us>
1 sibling, 0 replies; 3+ messages in thread
From: Tom Lane @ 2019-09-05 13:46 UTC (permalink / raw)
To: Mike Martin <redtux1@gmail.com>; +Cc: pgsql-sql@lists.postgresql.org
Mike Martin <redtux1@gmail.com> writes:
> I was always under the impression that a case expression could only be
> on the right side of a where expression ie:
> WHERE fieldname=<cse expression>
> Is this a postgres extention, cant find any documentation on this
SQL has always had two forms of CASE: you can do
CASE
WHEN boolean_expression1 THEN value1
[ WHEN boolean_expression2 THEN value2 ... ]
[ ELSE valueN ]
END
or you can do
CASE test_value
WHEN comparison_value1 THEN value1
[ WHEN comparison_value2 THEN value2 ... ]
[ ELSE valueN ]
END
The latter is effectively the same as
CASE
WHEN test_value = comparison_value1 THEN value1
[ WHEN test_value = comparison_value2 THEN value2 ... ]
[ ELSE valueN ]
END
except test_value is only supposed to be evaluated once.
This goes back at least as far as SQL-92.
It is documented, see
https://www.postgresql.org/docs/current/functions-conditional.html
regards, tom lane
^ permalink raw reply [nested|flat] 3+ messages in thread
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2019-09-05 11:04 Question about WHERE CASE Mike Martin <redtux1@gmail.com>
2019-09-05 11:42 ` Martin Stöcker <martin.stoecker@stb-datenservice.de>
2019-09-05 13:46 ` Tom Lane <tgl@sss.pgh.pa.us>
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