Function assign_collations_walker

src/backend/parser/parse_collate.c:257–779

* assign_collations_walker() * Recursive guts of collation processing. * * Nodes with no children (eg, Vars, Consts, Params) must have been marked * when built. All upper-level nodes are marked here. * * Note: if this is invoked directly on a List, it will attempt to infer a * common collation for all the list members. In particular, it will throw * error if there are conflicting explic

 * error if there are conflicting explicit collations for different members.
 */
static bool
assign_collations_walker(Node *node, assign_collations_context *context)
{
	assign_collations_context loccontext;
	Oid			collation;
	CollateStrength strength;
	int			location;

	/* Need do nothing for empty subexpressions */
	if (node == NULL)
		return false;

	/*
	 * Prepare for recursion.  For most node types, though not all, the first
	 * thing we do is recurse to process all nodes below this one. Each level
	 * of the tree has its own local context.
	 */
	loccontext.pstate = context->pstate;
	loccontext.collation = InvalidOid;
	loccontext.strength = COLLATE_NONE;
	loccontext.location = -1;
	/* Set these fields just to suppress uninitialized-value warnings: */
	loccontext.collation2 = InvalidOid;
	loccontext.location2 = -1;

	/*
	 * Recurse if appropriate, then determine the collation for this node.
	 *
	 * Note: the general cases are at the bottom of the switch, after various
	 * special cases.
	 */
	switch (nodeTag(node))
	{
		case T_CollateExpr:
			{
				/*
				 * COLLATE sets an explicitly derived collation, regardless of
				 * what the child state is.  But we must recurse to set up
				 * collation info below here.
				 */
				CollateExpr *expr = (CollateExpr *) node;

				(void) expression_tree_walker(node,
											  assign_collations_walker,
											  (void *) &loccontext);

				collation = expr->collOid;
				Assert(OidIsValid(collation));
				strength = COLLATE_EXPLICIT;
				location = expr->location;
			}
			break;
		case T_FieldSelect:
			{
				/*
				 * For FieldSelect, the result has the field's declared
				 * collation, independently of what happened in the arguments.
				 * (The immediate argument must be composite and thus not