Function select_common_collation

src/backend/parser/parse_collate.c:207–244

* select_common_collation() * Identify a common collation for a list of expressions. * * The expressions should all return the same datatype, else this is not * terribly meaningful. * * none_ok means that it is permitted to return InvalidOid, indicating that * no common collation could be identified, even for collatable datatypes. * Otherwise, an error is thrown for conflict of implicit c

 * operations").
 */
Oid
select_common_collation(ParseState *pstate, List *exprs, bool none_ok)
{
	assign_collations_context context;

	/* initialize context for tree walk */
	context.pstate = pstate;
	context.collation = InvalidOid;
	context.strength = COLLATE_NONE;
	context.location = -1;

	context.collation2 = InvalidOid;
	context.location2 = -1;

	/* and away we go */
	(void) assign_collations_walker((Node *) exprs, &context);

	/* deal with collation conflict */
	if (context.strength == COLLATE_CONFLICT)
	{
		if (none_ok)
			return InvalidOid;
		ereport(ERROR,
				(errcode(ERRCODE_COLLATION_MISMATCH),
				 errmsg("collation mismatch between implicit collations \"%s\" and \"%s\"",
						get_collation_name(context.collation),
						get_collation_name(context.collation2)),
				 errhint("You can choose the collation by applying the COLLATE clause to one or both expressions."),
				 parser_errposition(context.pstate, context.location2)));
	}

	/*
	 * Note: if strength is still COLLATE_NONE, we'll return InvalidOid, but
	 * that's okay because it must mean none of the expressions returned
	 * collatable datatypes.
	 */
	return context.collation;
}

/*
 * assign_collations_walker()