Re: SQL Join - MySQL/PostgreSQL difference? - Mailing list pgsql-sql

FYI:  Here are the table definitions:

CREATE TABLE TBLPEMDRUGLINK
(
    DRUGID                      VARCHAR(10) NOT NULL,
    MONOGRAPHID                 VARCHAR(10) NOT NULL,
    CONSTRAINT PK_TBLPEMDRUGLINK PRIMARY KEY (DRUGID, MONOGRAPHID)
);

CREATE TABLE TBLFDBMONO
(
    VERSIONID                   VARCHAR(10) NOT NULL,
    CATEGORY                    VARCHAR(10) NOT NULL,
    MONOGRAPHID                 VARCHAR(10) NOT NULL,
    SEQUENCENUMBER              SMALLINT NOT NULL,
    SECTIONCODE                 VARCHAR(1),
    LINETEXT                    VARCHAR(255),
    CONSTRAINT PK_TBLFDBMONO PRIMARY KEY (VERSIONID, CATEGORY,
MONOGRAPHID, SEQUENCENUMBER)
);

Running the following query:

Query1: SELECT sequencenumber,sectioncode,linetext
Query1:   FROM tblfdbmono fdb, tblpemdruglink pem WHERE
Query1:    fdb.monographid=pem.monographid AND
Query1:    fdb.versionid='FDB-PE' AND
Query1:    fdb.category='PEM' AND
Query1:    pem.drugid='DG-5039';

returns 0 rows.

However, the following two queries produce results:

Query2: SELECT * FROM tblpemdruglink WHERE drugid='DG-5039';

Query3: SELECT * FROM tblfdbmono WHERE
Query3:   monographid='2008' AND
Query3:   versionid='FDB-PE' AND
Query3:   category='PEM';

To my knowledge, Query1 is the join that should produce the same results
as the manual join represented by queries 2 & 3.

What's going on?

-Brice

Ian Harding wrote:
>
> Brice Ruth wrote:
>
> > Greetings.
> >
> > I'm working with a product provided by a third part that interfaces to
> > data housed in a database of your choice.  Previously, my choice was
> > MySQL - apparently it handled certain queries too slowly, so I'm giving
> > PostgreSQL a shot.  Here's the query:
> >
> > SELECT
> >   a.Number,
> >   a.Code,
> >   a.Text
> > FROM
> >   b,
> >   a
> > WHERE
> >   (b.Id = a.Id) AND
> >   (VersionId = 'key1') AND
> >   (Category = 'key2') AND
> >   (b.d_Id = 'key3')
> > ORDER BY
> >   a.Number;
> >
> > (my apologies: I had to 'mangle' the table/column names because of NDA)
> >
> > So my question is this: would this query operate differently in MySQL
> > than in PostgreSQL?  The reason I ask is that this query in MySQL
> > returns results, yet in PostgreSQL it does not.  I read a post about
> > PostgreSQL not supporting outer joins, but I don't have enough
> > experience with SQL to determine if this is such a query or not.  Please
> >
> > advise.
> >
> > Any help will be (as always) sincerely appreciated.
> >
> > --
> > Brice Ruth
> > WebProjkt, Inc.
> > VP, Director of Internet Technology
> > http://www.webprojkt.com/
>
> It should work the same in both.  The only thing I notice is that not all
> the field names are qualified with table names or aliases.  That can lead
> to ambiguity, but the query would blow up on both databases if that were a
> problem.
>
> Ian

--
Brice Ruth
WebProjkt, Inc.
VP, Director of Internet Technology
http://www.webprojkt.com/