Обсуждение: SQL query problem
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: 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 I will be appreciated for you help. ML
On Thu, Oct 09, 2003 at 20:52:58 +0100, 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 Probably you quoted the table name when you created it so that it is named _CON. However when you don't quote the name in later references _CON is converted to _con which is a different name that doesn't match any existing table. This behavior is contrary to the spec (lowercasing instead of uppercasing), but isn't going to change since uppercase names look ugly. A good general rule to follow is to either never quote names or always quote names. > > This is my 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, > 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 > > > I will be appreciated for you help. > > ML > > > > > ---------------------------(end of broadcast)--------------------------- > TIP 3: if posting/reading through Usenet, please send an appropriate > subscribe-nomail command to majordomo@postgresql.org so that your > message can get through to the mailing list cleanly
> 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
> > 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
Re: [SQL] SQL query problem (many table in FROM statement and many LEFT JOIN's)
От
Richard Huxton
Дата:
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