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Avoid a few more SET DATA TYPE table rewrites.

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When the new type is an unconstrained domain over the old type, we don't
need to rewrite the table.

Noah Misch and Robert Haas
This commit is contained in:
Robert Haas
2011-02-14 23:17:35 -05:00
parent 8e1124eeeb
commit 0d90dc16f8
2 changed files with 24 additions and 11 deletions
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20
src/backend/commands/tablecmds.c
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@ -6632,10 +6632,14 @@ ATPrepAlterColumnType(List **wqueue,
}
/*
* When the data type of a column is changed, a rewrite might not be require
* if the data type is being changed to its current type, or more interestingly
* to a type to which it is binary coercible. But we must check carefully that
* the USING clause isn't trying to insert some other value.
* When the data type of a column is changed, a rewrite might not be required
* if the new type is sufficiently identical to the old one, and the USING
* clause isn't trying to insert some other value. It's safe to skip the
* rewrite if the old type is binary coercible to the new type, or if the
* new type is an unconstrained domain over the old type. In the case of a
* constrained domain, we could get by with scanning the table and checking
* the constraint rather than actually rewriting it, but we don't currently
* try to do that.
*/
static bool
ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno)
@ -6649,6 +6653,14 @@ ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno)
return false;
else if (IsA(expr, RelabelType))
expr = (Node *) ((RelabelType *) expr)->arg;
else if (IsA(expr, CoerceToDomain))
{
CoerceToDomain *d = (CoerceToDomain *) expr;
if (GetDomainConstraints(d->resulttype) != NIL)
return true;
expr = (Node *) d->arg;
}
else
return true;
}