Alban Hertroys <dal...@solfertje.student.utwente.nl> writes:
> On 8 Nov 2010, at 16:18, Alexander Farber wrote:
>> alter table pref_users add constraint pref_users_medals_check check
>> (medals >= 0);
>>
>> has worked!
> To clarify a bit on this; if you add a constraint, you specify its name and
> what type of constraint it is, before specifying the actual constraint
> expression.
> Hence the need to add 'check' (the constraint type) between
> 'pref_users_medals_check' (the name) and '(medals >= 0)' (the expression).
One other thing that's maybe worth remembering about the syntax of
constraint clauses: the word CONSTRAINT is really used to introduce a
constraint name. If you want to create a constraint with no preselected
name, you leave off both the name and the word CONSTRAINT --- but you
still need the word(s) specifying the constraint type, such as CHECK or
FOREIGN KEY.
So either of these syntaxes are legal:
alter table pref_users add constraint pref_users_medals_check check (medals >=
0);
alter table pref_users add check (medals >= 0);
In the latter case the constraint will be created with some
system-selected name. (In fact, it looks like pref_users_medals_check
is exactly the name you'd get by default, if there were no such
constraint name already in use.)
regards, tom lane
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