List all constraints

SELECT DECODE (t.constraint_type,
'P', 'Primary',
'R', 'Foreign',
'U', 'Alternate',
'Unknown'
) "Key",
t.table_name "Tab", t.constraint_name "Cons", c.column_name "Col",
c.POSITION "Pos"
FROM user_constraints t, user_cons_columns c
WHERE t.constraint_type IN ('P', 'R', 'U')
AND t.table_name = c.table_name
AND t.constraint_name = c.constraint_name
ORDER BY t.table_name, t.constraint_type, c.POSITION;