====== Užitečné SQL příklady ======

===== COALESCE =====

<code sql>
select COALESCE(IDZakaz, '') from ...
select * from rozpocty_rozpocty where COALESCE(IDzakaz, '') = ''
</code>

===== EXISTS =====

Nepoužívat konrstrukce subselectů "not in (select ...)", ale predikát EXISTS.

<code sql>
select * from sklad_vc vc
  where 
    not exists (select * from sklad_prijemky prijemky where prijemky.idprijemka=vc.idprijemka)
</code>

===== CASE =====

<code sql>
select 
  CASE 
    WHEN (field = 1) THEN 'x' 
    WHEN (field = 2) THEN 'y' 
    ELSE 'z' 
  END 
from ...
</code>

===== SUBSTRING =====

<code sql>
select SUBSTRING(field FROM 1 FOR 5) from ...
</code>