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Re: Array string casts with SELECT but not SELECT DISTINCT - Mailing list pgsql-general

From	Ken Tanzer
Subject	Re: Array string casts with SELECT but not SELECT DISTINCT
Date	February 21, 2015 07:09:25
Msg-id	CAD3a31U7nm_cm2guJACy_r_LB0T+OJC9MK+bbfEffD+zmBmDww@mail.gmail.com Whole thread Raw
In response to	Re: Array string casts with SELECT but not SELECT DISTINCT (sridhar bamandlapally <sridhar.bn1@gmail.com>)
Responses	Re: Array string casts with SELECT but not SELECT DISTINCT
List	pgsql-general

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I'm not able to run this unless I'm the Postgres super user. But if I run it as such, it tells me that cast already exists anyway.

CREATE CAST (text AS varchar) WITH INOUT AS IMPLICIT;

ERROR: cast from type text to type character varying already exists

Of course this will work fine:

INSERT INTO foo (my_array) SELECT DISTINCT '{TEST}'::varchar[];

I was mostly surprised by having DISTINCT added to a SELECT make things break. It may be too obscure an issue to be worth adding, but nothing on the DISTINCT documentation suggests this possibility.

"If DISTINCT is specified, all duplicate rows are removed from the result set..."

http://www.postgresql.org/docs/9.0/static/sql-select.html#SQL-DISTINCT

Cheers,

Ken

On Fri, Feb 20, 2015 at 6:30 PM, sridhar bamandlapally <sridhar.bn1@gmail.com> wrote:

>>>ERROR: column "my_array" is of type character varying[] but expression is of type text

please try this below, may be this should help

CREATE CAST (text AS varchar) WITH INOUT AS IMPLICIT;

just for info:
actually this should be available in default

On Fri, Feb 20, 2015 at 9:48 AM, Ken Tanzer <ken.tanzer@gmail.com> wrote:
Hi. Here's a boiled down example of something that caught me by surprise:

ag_reach_test=> CREATE TEMP TABLE foo (my_array varchar[]);
CREATE TABLE
ag_reach_test=> INSERT INTO foo (my_array) SELECT '{TEST}';
INSERT 0 1
ag_reach_test=> SELECT my_array[1],array_length(my_array,1) FROM foo;
my_array | array_length
----------+--------------
TEST | 1
(1 row)

ag_reach_test=> INSERT INTO foo (my_array) SELECT DISTINCT '{TEST}';
ERROR: column "my_array" is of type character varying[] but expression is of type text
LINE 1: INSERT INTO foo (my_array) SELECT DISTINCT '{TEST}';
^
HINT: You will need to rewrite or cast the expression.

It's easy enough to add a cast, but I was curious if this was expected and desired behavior. Thanks.

Ken

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