SQLite

      /* Implement a co-routine that will return a single row of the result
      ** set on each invocation.
      */
      int addrTop = sqlite3VdbeCurrentAddr(v)+1;
      pItem->regReturn = ++pParse->nMem;
      sqlite3VdbeAddOp3(v, OP_InitCoroutine, pItem->regReturn, 0, addrTop);
      VdbeComment((v, "%s", pItem->pTab->zName));
      sqlite3VdbeAddOp1(v, OP_OpenPseudo, pItem->iCursor);
      sqlite3VdbeChangeP5(v, 1);
      pItem->addrFillSub = addrTop;
      sqlite3SelectDestInit(&dest, SRT_Coroutine, pItem->regReturn);
      explainSetInteger(pItem->iSelectId, (u8)pParse->iNextSelectId);
      sqlite3Select(pParse, pSub, &dest);
      pItem->pTab->nRowEst = (unsigned)pSub->nSelectRow;
      pItem->viaCoroutine = 1;
      sqlite3VdbeChangeP2(v, addrTop, dest.iSdst);
      pItem->regResult = dest.iSdst;
      sqlite3VdbeChangeP3(v, addrTop, dest.nSdst);
      sqlite3VdbeAddOp1(v, OP_EndCoroutine, pItem->regReturn);
      sqlite3VdbeJumpHere(v, addrTop-1);
      sqlite3ClearTempRegCache(pParse);
    }else{
      /* Generate a subroutine that will fill an ephemeral table with
      ** the content of this subquery.  pItem->addrFillSub will point
      ** to the address of the generated subroutine.  pItem->regReturn

    char *zDatabase;  /* Name of database holding this table */
    char *zName;      /* Name of the table */
    char *zAlias;     /* The "B" part of a "A AS B" phrase.  zName is the "A" */
    Table *pTab;      /* An SQL table corresponding to zName */
    Select *pSelect;  /* A SELECT statement used in place of a table name */
    int addrFillSub;  /* Address of subroutine to manifest a subquery */
    int regReturn;    /* Register holding return address of addrFillSub */
    int regResult;    /* Registers holding results of a co-routine */
    u8 jointype;      /* Type of join between this able and the previous */
    unsigned notIndexed :1;    /* True if there is a NOT INDEXED clause */
    unsigned isCorrelated :1;  /* True if sub-query is correlated */
    unsigned viaCoroutine :1;  /* Implemented as a co-routine */
    unsigned isRecursive :1;   /* True for recursive reference in WITH */
#ifndef SQLITE_OMIT_EXPLAIN
    u8 iSelectId;     /* If pSelect!=0, the id of the sub-select in EQP */

  rc = sqlite3VdbeCursorMoveto(pC);
  if( rc ) goto abort_due_to_error;
  if( pC->cacheStatus!=p->cacheCtr || (pOp->p5&OPFLAG_CLEARCACHE)!=0 ){
    if( pC->nullRow ){
      if( pCrsr==0 ){
        assert( pC->pseudoTableReg>0 );
        pReg = &aMem[pC->pseudoTableReg];
        if( pC->multiPseudo ){
          sqlite3VdbeMemShallowCopy(pDest, pReg+p2, MEM_Ephem);
          Deephemeralize(pDest);
          goto op_column_out;
        }
        assert( pReg->flags & MEM_Blob );
        assert( memIsValid(pReg) );
        pC->payloadSize = pC->szRow = avail = pReg->n;
        pC->aRow = (u8*)pReg->z;
      }else{
        MemSetTypeFlag(pDest, MEM_Null);
        goto op_column_out;

  pCx->pKeyInfo = pOp->p4.pKeyInfo;
  assert( pCx->pKeyInfo->db==db );
  assert( pCx->pKeyInfo->enc==ENC(db) );
  rc = sqlite3VdbeSorterInit(db, pCx);
  break;
}

/* Opcode: OpenPseudo P1 P2 P3 * P5
/* Opcode: OpenPseudo P1 P2 P3 * *
** Synopsis: content in r[P2@P3]
**
** Open a new cursor that points to a fake table that contains a single
** row of data.  The content of that one row in the content of memory
** register P2 when P5==0.  In other words, cursor P1 becomes an alias for the 
** MEM_Blob content contained in register P2.  When P5==1, then the
** row of data.  The content of that one row is the content of memory
** register P2.  In other words, cursor P1 becomes an alias for the 
** MEM_Blob content contained in register P2.
** row is represented by P3 consecutive registers beginning with P2.
**
** A pseudo-table created by this opcode is used to hold a single
** row output from the sorter so that the row can be decomposed into
** individual columns using the OP_Column opcode.  The OP_Column opcode
** is the only cursor opcode that works with a pseudo-table.
**
** P3 is the number of fields in the records that will be stored by
** the pseudo-table.
*/
case OP_OpenPseudo: {
  VdbeCursor *pCx;

  assert( pOp->p1>=0 );
  assert( pOp->p3>=0 );
  pCx = allocateCursor(p, pOp->p1, pOp->p3, -1, 0);
  if( pCx==0 ) goto no_mem;
  pCx->nullRow = 1;
  pCx->pseudoTableReg = pOp->p2;
  pCx->isTable = 1;
  pCx->multiPseudo = pOp->p5;
  assert( pOp->p5==0 );
  break;
}

/* Opcode: Close P1 * * * *
**
** Close a cursor previously opened as P1.  If P1 is not
** currently open, this instruction is a no-op.

  i8 iDb;               /* Index of cursor database in db->aDb[] (or -1) */
  u8 nullRow;           /* True if pointing to a row with no data */
  u8 rowidIsValid;      /* True if lastRowid is valid */
  u8 deferredMoveto;    /* A call to sqlite3BtreeMoveto() is needed */
  Bool useRandomRowid:1;/* Generate new record numbers semi-randomly */
  Bool isTable:1;       /* True if a table requiring integer keys */
  Bool isOrdered:1;     /* True if the underlying table is BTREE_UNORDERED */
  Bool multiPseudo:1;   /* Multi-register pseudo-cursor */
  sqlite3_vtab_cursor *pVtabCursor;  /* The cursor for a virtual table */
  i64 seqCount;         /* Sequence counter */
  i64 movetoTarget;     /* Argument to the deferred sqlite3BtreeMoveto() */
  i64 lastRowid;        /* Rowid being deleted by OP_Delete */
  VdbeSorter *pSorter;  /* Sorter object for OP_SorterOpen cursors */

  /* Cached information about the header for the data record that the

  /* The "break" point is here, just past the end of the outer loop.
  ** Set it.
  */
  sqlite3VdbeResolveLabel(v, pWInfo->iBreak);

  assert( pWInfo->nLevel<=pTabList->nSrc );
  for(i=0, pLevel=pWInfo->a; i<pWInfo->nLevel; i++, pLevel++){
    int k, last;
    VdbeOp *pOp;
    Index *pIdx = 0;
    struct SrcList_item *pTabItem = &pTabList->a[pLevel->iFrom];
    Table *pTab = pTabItem->pTab;
    assert( pTab!=0 );
    pLoop = pLevel->pWLoop;

    /* For a co-routine, change all OP_Column references to the table of
    ** the co-routine into OP_SCopy of result contained in a register.
    ** OP_Rowid becomes OP_Null.
    */
    if( pTabItem->viaCoroutine ){
      last = sqlite3VdbeCurrentAddr(v);
      k = pLevel->addrBody;
      pOp = sqlite3VdbeGetOp(v, k);
      for(; k<last; k++, pOp++){
        if( pOp->p1!=pLevel->iTabCur ) continue;
        if( pOp->opcode==OP_Column ){
          pOp->opcode = OP_SCopy;
          pOp->p1 = pOp->p2 + pTabItem->regResult;
          pOp->p2 = pOp->p3;
          pOp->p3 = 0;
        }else if( pOp->opcode==OP_Rowid ){
          pOp->opcode = OP_Null;
          pOp->p1 = 0;
          pOp->p3 = 0;
        }
      }
      continue;
    }

    /* Close all of the cursors that were opened by sqlite3WhereBegin.
    ** Except, do not close cursors that will be reused by the OR optimization
    ** (WHERE_OMIT_OPEN_CLOSE).  And do not close the OP_OpenWrite cursors
    ** created for the ONEPASS optimization.
    */
    if( (pTab->tabFlags & TF_Ephemeral)==0

    */
    if( pLoop->wsFlags & (WHERE_INDEXED|WHERE_IDX_ONLY) ){
      pIdx = pLoop->u.btree.pIndex;
    }else if( pLoop->wsFlags & WHERE_MULTI_OR ){
      pIdx = pLevel->u.pCovidx;
    }
    if( pIdx && !db->mallocFailed ){
      int k, last;
      VdbeOp *pOp;

      last = sqlite3VdbeCurrentAddr(v);
      k = pLevel->addrBody;
      pOp = sqlite3VdbeGetOp(v, k);
      for(; k<last; k++, pOp++){
        if( pOp->p1!=pLevel->iTabCur ) continue;
        if( pOp->opcode==OP_Column ){
          int x = pOp->p2;