Function transformAExprNullIf

src/backend/parser/parse_expr.c:1055–1095

}

static Node *
transformAExprNullIf(ParseState *pstate, A_Expr *a)
{
	Node	   *lexpr = transformExprRecurse(pstate, a->lexpr);
	Node	   *rexpr = transformExprRecurse(pstate, a->rexpr);
	OpExpr	   *result;

	result = (OpExpr *) make_op(pstate,
								a->name,
								lexpr,
								rexpr,
								pstate->p_last_srf,
								a->location);

	/*
	 * The comparison operator itself should yield boolean ...
	 */
	if (result->opresulttype != BOOLOID)
		ereport(ERROR,
				(errcode(ERRCODE_DATATYPE_MISMATCH),
				 errmsg("NULLIF requires = operator to yield boolean"),
				 parser_errposition(pstate, a->location)));
	if (result->opretset)
		ereport(ERROR,
				(errcode(ERRCODE_DATATYPE_MISMATCH),
		/* translator: %s is name of a SQL construct, eg NULLIF */
				 errmsg("%s must not return a set", "NULLIF"),
				 parser_errposition(pstate, a->location)));

	/*
	 * ... but the NullIfExpr will yield the first operand's type.
	 */
	result->opresulttype = exprType((Node *) linitial(result->args));

	/*
	 * We rely on NullIfExpr and OpExpr being the same struct
	 */
	NodeSetTag(result, T_NullIfExpr);

	return (Node *) result;
}

static Node *
transformAExprIn(ParseState *pstate, A_Expr *a)