Function exec_eval_expr

src/pl/plpgsql/src/pl_exec.c:5614–5691

---------- * exec_eval_expr Evaluate an expression and return * the result Datum, along with data type/typmod. * * NOTE: caller must do exec_eval_cleanup when done with the Datum. * ---------- */

 * ----------
 */
static Datum
exec_eval_expr(PLpgSQL_execstate *estate,
			   PLpgSQL_expr *expr,
			   bool *isNull,
			   Oid *rettype,
			   int32 *rettypmod)
{
	Datum		result = 0;
	int			rc;
	Form_pg_attribute attr;

	/*
	 * If first time through, create a plan for this expression.
	 */
	if (expr->plan == NULL)
		exec_prepare_plan(estate, expr, CURSOR_OPT_PARALLEL_OK);

	/*
	 * If this is a simple expression, bypass SPI and use the executor
	 * directly
	 */
	if (exec_eval_simple_expr(estate, expr,
							  &result, isNull, rettype, rettypmod))
		return result;

	/*
	 * Else do it the hard way via exec_run_select
	 */
	rc = exec_run_select(estate, expr, 2, NULL);
	if (rc != SPI_OK_SELECT)
		ereport(ERROR,
				(errcode(ERRCODE_WRONG_OBJECT_TYPE),
				 errmsg("query did not return data"),
				 errcontext("query: %s", expr->query)));

	/*
	 * Check that the expression returns exactly one column...
	 */
	if (estate->eval_tuptable->tupdesc->natts != 1)
		ereport(ERROR,
				(errcode(ERRCODE_SYNTAX_ERROR),
				 errmsg_plural("query returned %d column",
							   "query returned %d columns",
							   estate->eval_tuptable->tupdesc->natts,
							   estate->eval_tuptable->tupdesc->natts),
				 errcontext("query: %s", expr->query)));

	/*
	 * ... and get the column's datatype.
	 */
	attr = TupleDescAttr(estate->eval_tuptable->tupdesc, 0);
	*rettype = attr->atttypid;
	*rettypmod = attr->atttypmod;

	/*
	 * If there are no rows selected, the result is a NULL of that type.
	 */
	if (estate->eval_processed == 0)