Function ExecInitExpr

src/backend/executor/execExpr.c:134–163

* ExecInitExpr: prepare an expression tree for execution * * This function builds and returns an ExprState implementing the given * Expr node tree. The return ExprState can then be handed to ExecEvalExpr * for execution. Because the Expr tree itself is read-only as far as * ExecInitExpr and ExecEvalExpr are concerned, several different executions * of the same plan tree can occur concurren

 * although ExecQual and ExecCheck will accept one (and treat it as "true").
 */
ExprState *
ExecInitExpr(Expr *node, PlanState *parent)
{
	ExprState  *state;
	ExprEvalStep scratch = {0};

	/* Special case: NULL expression produces a NULL ExprState pointer */
	if (node == NULL)
		return NULL;

	/* Initialize ExprState with empty step list */
	state = makeNode(ExprState);
	state->expr = node;
	state->parent = parent;
	state->ext_params = NULL;

	/* Insert EEOP_*_FETCHSOME steps as needed */
	ExecInitExprSlots(state, (Node *) node);

	/* Compile the expression proper */
	ExecInitExprRec(node, state, &state->resvalue, &state->resnull);

	/* Finally, append a DONE step */
	scratch.opcode = EEOP_DONE;
	ExprEvalPushStep(state, &scratch);

	ExecReadyExpr(state);

	return state;
}

/*
 * ExecInitExprWithParams: prepare a standalone expression tree for execution