接前面，这次重点分析 ExecScan:

其for 循环内部：

for (;;)    {        TupleTableSlot *slot;        CHECK_FOR_INTERRUPTS();        slot = ExecScanFetch(node, accessMtd, recheckMtd);        /*         * if the slot returned by the accessMtd contains NULL, then it means         * there is nothing more to scan so we just return an empty slot,         * being careful to use the projection result slot so it has correct         * tupleDesc.         */        if (TupIsNull(slot))        {            if (projInfo)                return ExecClearTuple(projInfo->pi_slot);            else                return slot;        }        ...    }

接着来看 ExecScanFetch:

/* * ExecScanFetch -- fetch next potential tuple * * This routine is concerned with substituting a test tuple if we are * inside an EvalPlanQual recheck.    If we aren't, just execute * the access method's next-tuple routine. */static inline TupleTableSlot *ExecScanFetch(ScanState *node,              ExecScanAccessMtd accessMtd,              ExecScanRecheckMtd recheckMtd){    EState       *estate = node->ps.state;    if (estate->es_epqTuple != NULL)    {        /*         * We are inside an EvalPlanQual recheck.  Return the test tuple if         * one is available, after rechecking any access-method-specific         * conditions.         */        Index        scanrelid = ((Scan *) node->ps.plan)->scanrelid;        Assert(scanrelid > 0);        if (estate->es_epqTupleSet[scanrelid - 1])        {            TupleTableSlot *slot = node->ss_ScanTupleSlot;            /* Return empty slot if we already returned a tuple */            if (estate->es_epqScanDone[scanrelid - 1])                return ExecClearTuple(slot);            /* Else mark to remember that we shouldn't return more */            estate->es_epqScanDone[scanrelid - 1] = true;            /* Return empty slot if we haven't got a test tuple */            if (estate->es_epqTuple[scanrelid - 1] == NULL)                return ExecClearTuple(slot);            /* Store test tuple in the plan node's scan slot */            ExecStoreTuple(estate->es_epqTuple[scanrelid - 1],                           slot, InvalidBuffer, false);            /* Check if it meets the access-method conditions */            if (!(*recheckMtd) (node, slot))                ExecClearTuple(slot);    /* would not be returned by scan */            return slot;        }    }    /*     * Run the node-type-specific access method function to get the next tuple     */    return (*accessMtd) (node);}

上述的 ＜(estate->es_epqTuple != NULL)＞ 条件未能得到满足，所以

直接奔这个去了： return (*accessMtd) (node);

前面已经知道，因为没有index，所以就执行了：static TupleTableSlot * SeqNext(SeqScanState *node)