From: Mike Mascari <mascarm@mascari.com>
To: pgsql-interfaces@postgresql.org
Subject: Pattern matching fun via ODBC
Date: Mon, 20 Dec 1999 02:09:59 -0500
Message-ID: <385DD647.FE504F2B@mascari.com> (raw)
Hello,
I just thought I should bring this to the attention of the
mailing list. About a week ago I posted a problem I was
having with Microsoft Access 97 and the PostgreSQL ODBC
driver (6.40.0006) with respect to the use of a LIKE
expression (to which no one responded, BTW). A query such as
this:
SELECT workorders.workorder, workorders.workorderno,
equipment.assetno, equipment.controlno
FROM workorders, equipment
WHERE equipment.assetno LIKE '%214%'
AND workorders.equipment=equipment.equipment
ORDER BY workorders.workorder;
gets re-written by Access as this:
"SELECT "workorders"."workorder","equipment"."equipment"
FROM "equipment","workorders"
WHERE (("equipment"."assetno" = '%214%' )
AND ("workorders"."equipment" = "equipment"."equipment" ) )
ORDER BY "workorders"."workorder"
which is obviously NOT equivalent. I don't know whether to
blame Access 97 or the ODBC driver, but I'm leaning toward
Microsoft. Anyway, in order to get around this, I used the
following query:
SELECT workorders.workorder, workorders.workorderno,
equipment.assetno, equipment.controlno
FROM workorders, equipment
WHERE InStr(equipment.assetno, '214') > 0
AND workorders.equipment=equipment.equipment
ORDER BY workorders.workorder;
This was rewritten by Access 97 as:
"SELECT "workorders"."workorder","equipment"."equipment"
FROM "workorders","equipment"
WHERE (({fn locate('214' ,"equipment"."assetno" ,1)}> 0 )
AND ("workorders"."equipment" = "equipment"."equipment" ) )
ORDER BY "workorders"."workorder"
Well, this is a problem. Because, according to my ODBC 2.0
specs, LOCATE() should only contain 2 parameters as in:
LOCATE(string1, string2)
not three. I also see that the ODBC driver is translating fn
LOCATE ODBC client calls into strpos() calls on the server.
In Convert.c:
/* How to map ODBC scalar functions {fn func(args)} to
Postgres */
/* This is just a simple substitution */
char *mapFuncs[][2] = {
{ "CONCAT", "textcat" },
{ "LCASE", "lower" },
{ "LOCATE", "strpos" },
{ "LENGTH", "textlen" },
{ "LTRIM", "ltrim" },
Unfortunately, PostgreSQL doesn't have a strpos() routine of
the type:
int4 strpos(text, text, int4)
so I created one and everything now works. But I was just
wondering what (if anything) should be done about it. It
would be really simple to add a strpos() function to the
system catalog which takes a starting character parameter,
but should that be PostgreSQL's responsibility? The thing
is, I know of no other way to perform simple %pattern% type
matching via ODBC without using pass-through queries.
Any comments?
Mike Mascari
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To: pgsql-interfaces@postgresql.org
Cc: mascarm@mascari.com
Subject: Re: Pattern matching fun via ODBC
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