Predikßt EXISTS (SQL)

predikßt_EXISTS ::= EXISTS ( dotazov²_v²raz )

Predikßt EXISTS °φkß, zda v odpov∞di na dotazov² v²raz (subdotaz) je alespo≥ jeden zßznam.

P°φklad pou₧itφ:

Vyberte firmy, kterΘ nemajφ ₧ßdnΘ faktury

SELECT nazev
FROM Firmy F
WHERE NOT EXISTS (SELECT * FROM Faktury A
                  WHERE A.nazev=F.nazev)

Pou₧itφ mimo SELECT:

IF EXISTS (SELECT admin_enabled FROM System 
           WHERE (admin_name=usr)AND(admin_password=pwd)AND(admin_enabled IS TRUE)) 
  THEN ...