Para testar use posgres BD tenis tabela jtest (jogadores)
NOTA: os comandos de atualizacao (update) violam uma constraint
definida anteriormente e nao sao executados

alter table jtest
add constraint chk_j1 check (vits > tit_s)
0 row(s) affected by your update/insert/delete command 
update jtest set vits =53 where numj = 29
ERROR: new row for relation "jtest" violates check constraint "chk_j1"
----------------------------------------------------------------------
alter table jtest
add constraint chk_j2 check (ano_p -ano_n > 15 and ano_n >66)
ERROR: check constraint "chk_j2" is violated by some row
-------------------------------------------------------------
alter table jtest
drop constraint chk_j2 
alter table jtest
add constraint chk_j2 check (ano_p -ano_n > 15 and ano_n >= 66)
0 row(s) affected by your update/insert/delete command 
update jtest set ano_p= 84 where numj = 29
ERROR: new row for relation "jtest" violates check constraint "chk_j2"
----------------------------------------------------------------------
-- Pesquisa no Google: "Postgres find constraint names". Achei:
SELECT conname, contype
FROM pg_catalog.pg_constraint c
JOIN pg_class t ON t.oid = c.conrelid
WHERE t.relname ='jtest'
conname contype
chk1    c
chk_j2  c

2 rows returned by your query in 0.0 secs 
-----------------------------------------------------------------
numj    nome    pnome   pais    ano_n   ano_p   cid_n   cid_res tit_s   tit_d   vits    derrs   natp
--------------------------------------------------------------------
Constraint como "expressao regular":

alter table jtest
add constraint chk_j3 check (pais ~ '[A-Z]{3}') --  exatamente 3 letras maiusculas
updOBte jtest set pais = 'swe' where numj = 19
ERROR: new row for relation "jtest" violates check constraint "chk_j3"
-------------------------------------------------------------
update jtest set pais = 'SWe' where numj = 19
ERROR: new row for relation "jtest" violates check constraint "chk_j3
--------------------------------------------------------------------
update jtest set pais = 'BRAS' where numj = 19
ERROR: value too long for type character(3)
-------------------------------------------------------------
update jtest set pais = 'BR'
where numj = 16
ERROR: new row for relation "jtest" violates check constraint "chk_j3"
----------------------------------------------------------------------
*******************************************************************
Pesquisa no Google: "Postgres find constraint names". 
Achei:
SELECT conname, contype
FROM pg_catalog.pg_constraint c
JOIN pg_class t ON t.oid = c.conrelid
WHERE t.relname ='jtest'
*****************************************************************
alter table jtest
add constraint chk_email_
   check (email ~ '^[a-z]+\.?[a-z]+@([a-z]+\.[a-z]+\.[a-z]+)|([a-z]+\.[a-z]+)$')
update jtest
set email = 'stefan\.edberg@ic.unicamp.swe'
where numj = 19

select numj,pnome, nome,pais,email
 from jtest
 order by numj
***************************************************************
-- nenhum funcionario pode ter salario superior ao do chefe
alter table funcionarios
add constraint chk_sal 
check (sal <= (select f1.sal
from funcionarios f1
where f1.numf = funcionarios.numc))
ERROR: cannot use subquery in check constraint
************************************************