Function transformAExprIn

src/backend/parser/parse_expr.c:1097–1253

}

static Node *
transformAExprIn(ParseState *pstate, A_Expr *a)
{
	Node	   *result = NULL;
	Node	   *lexpr;
	List	   *rexprs;
	List	   *rvars;
	List	   *rnonvars;
	bool		useOr;
	ListCell   *l;

	/*
	 * If the operator is <>, combine with AND not OR.
	 */
	if (strcmp(strVal(linitial(a->name)), "<>") == 0)
		useOr = false;
	else
		useOr = true;

	/*
	 * We try to generate a ScalarArrayOpExpr from IN/NOT IN, but this is only
	 * possible if there is a suitable array type available.  If not, we fall
	 * back to a boolean condition tree with multiple copies of the lefthand
	 * expression.  Also, any IN-list items that contain Vars are handled as
	 * separate boolean conditions, because that gives the planner more scope
	 * for optimization on such clauses.
	 *
	 * First step: transform all the inputs, and detect whether any contain
	 * Vars.
	 */
	lexpr = transformExprRecurse(pstate, a->lexpr);
	rexprs = rvars = rnonvars = NIL;
	foreach(l, (List *) a->rexpr)
	{
		Node	   *rexpr = transformExprRecurse(pstate, lfirst(l));

		rexprs = lappend(rexprs, rexpr);
		if (contain_vars_of_level(rexpr, 0))
			rvars = lappend(rvars, rexpr);
		else
			rnonvars = lappend(rnonvars, rexpr);
	}

	/*
	 * ScalarArrayOpExpr is only going to be useful if there's more than one
	 * non-Var righthand item.
	 */
	if (list_length(rnonvars) > 1)
	{
		List	   *allexprs;
		Oid			scalar_type;
		Oid			array_type;

		/*
		 * Try to select a common type for the array elements.  Note that
		 * since the LHS' type is first in the list, it will be preferred when
		 * there is doubt (eg, when all the RHS items are unknown literals).
		 *