Function ExecInitExprRec

src/backend/executor/execExpr.c:911–2513

* Append the steps necessary for the evaluation of node to ExprState->steps, * possibly recursing into sub-expressions of node. * * node - expression to evaluate * state - ExprState to whose ->steps to append the necessary operations * resv / resnull - where to store the result of the node into */

 * resv / resnull - where to store the result of the node into
 */
static void
ExecInitExprRec(Expr *node, ExprState *state,
				Datum *resv, bool *resnull)
{
	ExprEvalStep scratch = {0};

	/* Guard against stack overflow due to overly complex expressions */
	check_stack_depth();

	/* Step's output location is always what the caller gave us */
	Assert(resv != NULL && resnull != NULL);
	scratch.resvalue = resv;
	scratch.resnull = resnull;

	/* cases should be ordered as they are in enum NodeTag */
	switch (nodeTag(node))
	{
		case T_Var:
			{
				Var		   *variable = (Var *) node;

				if (variable->varattno == InvalidAttrNumber)
				{
					/* whole-row Var */
					ExecInitWholeRowVar(&scratch, variable, state);
				}
				else if (variable->varattno <= 0)
				{
					/* system column */
					scratch.d.var.attnum = variable->varattno;
					scratch.d.var.vartype = variable->vartype;
					switch (variable->varno)
					{
						case INNER_VAR:
							scratch.opcode = EEOP_INNER_SYSVAR;
							break;
						case OUTER_VAR:
							scratch.opcode = EEOP_OUTER_SYSVAR;
							break;

							/* INDEX_VAR is handled by default case */

						default:
							scratch.opcode = EEOP_SCAN_SYSVAR;
							break;
					}
				}
				else
				{
					/* regular user column */
					scratch.d.var.attnum = variable->varattno - 1;
					scratch.d.var.vartype = variable->vartype;
					switch (variable->varno)
					{
						case INNER_VAR:
							scratch.opcode = EEOP_INNER_VAR;
							break;
						case OUTER_VAR: