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December 30, 2011 13:22
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Postgresql function to generate unique alpha-numeric codes
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-- Actually, if UNIQUE is defined on the col, there is no need to store previous codes | |
-- It will fail to insert due to uniqueness contraint when all possible codes are exhausted | |
-- Use as a column default... | |
-- CREATE TABLE foo (id CHAR(6) DEFAULT AlphaNumericSerial() UNIQUE); | |
CREATE OR REPLACE FUNCTION AlphaNumericSerial() | |
RETURNS char(6) AS $$ | |
DECLARE _serial char(6); _i int; _chars char(36) = 'abcdefghijklmnopqrstuvwxyz0123456789'; | |
BEGIN | |
_serial = ''; | |
FOR _i in 1 .. 6 LOOP | |
_serial = _serial || substr(_chars, int4(random() * length(_chars)), 1); | |
END LOOP; | |
RETURN lower(_serial); | |
END; | |
$$ LANGUAGE plpgsql VOLATILE; |
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There is a slight issue with this code. The
int4(random() * length(_chars))
will return values from 0 to 36 meaning that occasionally the index will fall out of the scope of 36 characters (more specifically this will happen when it returns 0 as substr counts position in string from 1). In turn, the whole function will return some values that have less then 6 chars.The following works as expected
int4(floor(random() * length(_chars))) + 1
. Meaning it will return values in the range of 1 to 36.