... nebo se to da rict nazorneji, LEFT JOIN melo byt LEFT OUTER JOIN, a to znamena, ze se z leve tabulky vyberou i ty zaznamy, ke kterym v prave tabulce nic neni. Tedy nejdriv se udela LEFT OUTER JOIN podle podminky v ON, a pak se teprve na vysledek aplikuje podminka ve WHERE.
Cili v tomto pripade LEFT OUTER JOIN da do "zam" NULL pro ty zaznamy z leve tabulky, pro ktere podminka v ON neuspela, a pak WHERE vybere prave tyto zaznamy. Pro info o OUTER JOINECHech viz treba http://www.praetoriate.com/oracle_tips_outer_joins.htm obcas je to dost uzitecna vec. Makub Pavel Kolesnikov wrote:
protoze LEFT JOIN pavel On 15/03/06, Jan Medek <[EMAIL PROTECTED]> wrote:Nejak se mi to nezda cele. Kdyz zam IS NULL, jak se muze zam.id rovnat res.id? Pavel Kolesnikov napsal(a):On 15/03/06, Ondřej Fafejta KYBERIE <[EMAIL PROTECTED]> wrote:2. EQL dotaz typu: SELECT res FROM Osoba res LEFT JOIN Zamestnanec zam WHERE res.id=zam.id AND zam IS NULL To ovšem nefunguje.Mozna Vam uplne neporadim, ponevadz nevim presne jak funguje EQL, ale v SQL byste spravne mel JOIN-ovaci podminku hodit do LEFT JOIN ON namisto WHERE, pak by to melo fungovat. Tedy spis: SELECT res FROM Osoba res LEFT JOIN Zamestnanec zam ON res.id=zam.id WHERE zam IS NULL Pavel
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