SQL query problem

fine). PG returns: ERROR: Relation "_con" does not exist

This is my query:

SELECT
_CON.con_id,

Please make sure you get the quoting right regarding table
names. PostgreSQL will fold _CON into _con unless quoted
"_CON". So, it may be that you created the table with quotes
("_CON"). Now, in your query you don't use quotes and thusly
it is looking for a _con table. The simple rule of thumb is to
either always or never use quotes.

HTH,
Karsten
--
GPG key ID E4071346 @ wwwkeys.pgp.net
E167 67FD A291 2BEA 73BD 4537 78B9 A9F9 E407 1346

Marek,

Not sure but, try switching the lines

db_data.mda_mod_con _CON,
db_data.set_mda_fue _FUE

with

db_data.set_mda_fue _FUE,
db_data.mda_mod_con _CON

so there query is:

SELECT
_CON.con_id,
_MOD.mod_ty,
_VER.version,
_YEA.year,
_CON.dri_id,
_CON.man_cod,
_ENG.eng_pow
FROM
db_data.mda_mod _MOD,
db_data.mda_mak_eng _ENG,
db_data.set_mda_fue _FUE,
db_data.mda_mod_con _CON
LEFT JOIN db_data.mda_mod_ver _VER ON _VER.ver_id =
_CON.ver_id
LEFT JOIN db_data.mda_mod_yea _YEA ON _YEA.yea_id =
_CON.yea_id
WHERE
_MOD.mod_id = '283' AND
_CON.mod_id = _MOD.mod_id AND
_CON.psd <= NOW() AND
_CON.ped > NOW() AND
_ENG.eng_id = _CON.eng_id AND
_ENG.eng_fue = _FUE.fue_id

--- Marek Lewczuk <newsy@lewczuk.com> wrote:

Hello,
I'm in the middle of the migration process from
MySQL to PostgreSQL and
I cannot understand why this query isn't working (in
MySQL it's working
fine). PG returns: ERROR: Relation "_con" does not
exist

This is my query:

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SELECT
_CON.con_id,

Please make sure you get the quoting right regarding table
names. PostgreSQL will fold _CON into _con unless quoted
"_CON". So, it may be that you created the table with quotes
("_CON"). Now, in your query you don't use quotes and thusly
it is looking for a _con table. The simple rule of thumb is
to either always or never use quotes.

I don't think that this is the solution, becouse the query:

SELECT
_CON.con_id,
_MOD.mod_ty,
_CON.dri_id,
_CON.man_cod,
_ENG.eng_pow
FROM
db_data.mda_mod _MOD,
db_data.mda_mod_con _CON,
db_data.mda_mak_eng _ENG,
db_data.set_mda_fue _FUE
WHERE
_MOD.mod_id = '283' AND
_CON.mod_id = _MOD.mod_id AND
_CON.psd <= NOW() AND
_CON.ped > NOW() AND
_ENG.eng_id = _CON.eng_id AND
_ENG.eng_fue = _FUE.fue_id

...is working fine. I belive that this some problem with LEFT JOIN and
FROM statement. If I will rewrite this query:

SELECT
_CON.con_id,
_MOD.mod_ty,
_VER.version,
_YEA.year,
_CON.dri_id,
_CON.man_cod,
_ENG.eng_pow
FROM
db_data.mda_mod _MOD
JOIN db_data.mda_mod_con _CON ON _CON.mod_id = _MOD.mod_id AND
_CON.psd <= NOW() AND _CON.ped > NOW()
JOIN db_data.mda_mak_eng _ENG ON _ENG.eng_id = _CON.eng_id
JOIN db_data.set_mda_fue _FUE ON _ENG.eng_fue = _FUE.fue_id
LEFT JOIN db_data.mda_mod_ver _VER ON _VER.ver_id = _CON.ver_id
LEFT JOIN db_data.mda_mod_yea _YEA ON _YEA.yea_id = _CON.yea_id
WHERE
_MOD.mod_id = '283'

... It also working fine. !!!! The question is, why my first query isn't
working:

SELECT
_CON.con_id,
_MOD.mod_ty,
_VER.version,
_YEA.year,
_CON.dri_id,
_CON.man_cod,
_ENG.eng_pow
FROM
db_data.mda_mod _MOD,
db_data.mda_mod_con _CON,
db_data.mda_mak_eng _ENG,
db_data.set_mda_fue _FUE
LEFT JOIN db_data.mda_mod_ver _VER ON _VER.ver_id = _CON.ver_id
LEFT JOIN db_data.mda_mod_yea _YEA ON _YEA.yea_id = _CON.yea_id
WHERE
_MOD.mod_id = '283' AND
_CON.mod_id = _MOD.mod_id AND
_CON.psd <= NOW() AND
_CON.ped > NOW() AND
_ENG.eng_id = _CON.eng_id AND
_ENG.eng_fue = _FUE.fue_id

On Friday 10 October 2003 08:53, Marek Lewczuk wrote:

SELECT
_CON.con_id,

Please make sure you get the quoting right regarding table
names. PostgreSQL will fold _CON into _con unless quoted
"_CON". So, it may be that you created the table with quotes
("_CON"). Now, in your query you don't use quotes and thusly
it is looking for a _con table. The simple rule of thumb is
to either always or never use quotes.

I don't think that this is the solution, becouse the query:

SELECT
_CON.con_id,
_MOD.mod_ty,
_CON.dri_id,
_CON.man_cod,
_ENG.eng_pow
FROM
db_data.mda_mod _MOD,
db_data.mda_mod_con _CON,
db_data.mda_mak_eng _ENG,
db_data.set_mda_fue _FUE
WHERE
_MOD.mod_id = '283' AND
_CON.mod_id = _MOD.mod_id AND
_CON.psd <= NOW() AND
_CON.ped > NOW() AND
_ENG.eng_id = _CON.eng_id AND
_ENG.eng_fue = _FUE.fue_id

...is working fine. I belive that this some problem with LEFT JOIN and
FROM statement. If I will rewrite this query:

I think what's happening here is the fact that if you use explicit joins in a
query that forces the order of the joins. You originally had:

db_data.mda_mod _MOD,
db_data.mda_mod_con _CON,
db_data.mda_mak_eng _ENG,
db_data.set_mda_fue _FUE
LEFT JOIN db_data.mda_mod_ver _VER ON _VER.ver_id = _CON.ver_id
LEFT JOIN db_data.mda_mod_yea _YEA ON _YEA.yea_id = _CON.yea_id
which was being parsed as something like:

( (_FUE LEFT JOIN _VER)
LEFT JOIN _YEA ),
_MOD, _CON, ENG

Of course, if it tries to evaluate in this order it can't see _CON from the
innermost brackets.

I believe the "force planner order" is configurable in the forthcoming 7.4

--
Richard Huxton
Archonet Ltd

"Marek Lewczuk" <newsy@lewczuk.com> writes:

... It also working fine. !!!! The question is, why my first query isn't
working:

SELECT
_CON.con_id,
_MOD.mod_ty,
_VER.version,
_YEA.year,
_CON.dri_id,
_CON.man_cod,
_ENG.eng_pow
FROM
db_data.mda_mod _MOD,
db_data.mda_mod_con _CON,
db_data.mda_mak_eng _ENG,
db_data.set_mda_fue _FUE
LEFT JOIN db_data.mda_mod_ver _VER ON _VER.ver_id = _CON.ver_id
LEFT JOIN db_data.mda_mod_yea _YEA ON _YEA.yea_id = _CON.yea_id
WHERE
_MOD.mod_id = '283' AND
_CON.mod_id = _MOD.mod_id AND
_CON.psd <= NOW() AND
_CON.ped > NOW() AND
_ENG.eng_id = _CON.eng_id AND
_ENG.eng_fue = _FUE.fue_id

The reason that works in MySQL and fails in Postgres is that MySQL isn't
compliant with the SQL standard. The standard says that the above FROM
clause means that _FUE is left-joined to _VER, then that result is
left-joined to _YEA, then the _MOD, _CON, and _ENG tables are joined to
that result (in no particular order). You get the error because the
LEFT JOIN ON clauses refer to _CON which is not part of what they are
joining.

I believe that MySQL interprets the above statement as "join the tables
in the order listed in the FROM clause", that is they join
_MOD/_CON/_ENG/_FUE, then left-join _VER to that result, etc. This is a
hangover from days when they didn't actually have a query planner.
Unfortunately, it's not SQL, it's only something that looks like SQL.

regards, tom lane