SQLite

  if( p && pIndexedBy->n>0 ){
    struct SrcList_item *pItem;
    assert( p->nSrc>0 );
    pItem = &p->a[p->nSrc-1];
    assert( pItem->fg.notIndexed==0 );
    assert( pItem->fg.isIndexedBy==0 );
    assert( pItem->fg.isTabFunc==0 );
    if( pIndexedBy->n>=1 && !pIndexedBy->z ){
    if( pIndexedBy->n==1 && !pIndexedBy->z ){
      if( pIndexedBy->n==1 ){
      /* A "NOT INDEXED" clause was supplied. See parse.y 
      ** construct "indexed_opt" for details. */
      pItem->fg.notIndexed = 1;
        pItem->fg.notIndexed = 1;
      }else{
        assert( pIndexedBy->n==2 );
        pItem->fg.useAutoIdx = 1;
      }
    }else{
      pItem->u1.zIndexedBy = sqlite3NameFromToken(pParse->db, pIndexedBy);
      pItem->fg.isIndexedBy = 1;
    }
  }
}

seltablist(A) ::= stl_prefix(A) nm(Y) dbnm(D) LP exprlist(E) RP as(Z)
                  on_opt(N) using_opt(U). {
  A = sqlite3SrcListAppendFromTerm(pParse,A,&Y,&D,&Z,0,N,U);
  sqlite3SrcListFuncArgs(pParse, A, E);
}
%ifndef SQLITE_OMIT_SUBQUERY
  seltablist(A) ::= stl_prefix(A) LP select(S) RP
                    as(Z) on_opt(N) using_opt(U). {
                    as(Z) indexed_opt(I) on_opt(N) using_opt(U). {
    A = sqlite3SrcListAppendFromTerm(pParse,A,0,0,&Z,S,N,U);
    sqlite3SrcListIndexedBy(pParse, A, &I);
  }
  seltablist(A) ::= stl_prefix(A) LP seltablist(F) RP
                    as(Z) on_opt(N) using_opt(U). {
                    as(Z) indexed_opt(I) on_opt(N) using_opt(U). {
    if( A==0 && Z.n==0 && N==0 && U==0 ){
      A = F;
    }else if( F->nSrc==1 ){
      A = sqlite3SrcListAppendFromTerm(pParse,A,0,0,&Z,0,N,U);
      if( A ){
        struct SrcList_item *pNew = &A->a[A->nSrc-1];
        struct SrcList_item *pOld = F->a;
        pNew->zName = pOld->zName;
        pNew->zDatabase = pOld->zDatabase;
        pNew->pSelect = pOld->pSelect;
        pOld->zName = pOld->zDatabase = 0;
        pOld->pSelect = 0;
      }
      sqlite3SrcListDelete(pParse->db, F);
    }else{
      Select *pSubquery;
      sqlite3SrcListShiftJoinType(F);
      pSubquery = sqlite3SelectNew(pParse,0,F,0,0,0,0,SF_NestedFrom,0);
      A = sqlite3SrcListAppendFromTerm(pParse,A,0,0,&Z,pSubquery,N,U);
    }
    sqlite3SrcListIndexedBy(pParse, A, &I);
  }
%endif  SQLITE_OMIT_SUBQUERY

%type dbnm {Token}
dbnm(A) ::= .          {A.z=0; A.n=0;}
dbnm(A) ::= DOT nm(X). {A = X;}

// normally illegal. The sqlite3SrcListIndexedBy() function 
// recognizes and interprets this as a special case.
//
%type indexed_opt {Token}
indexed_opt(A) ::= .                 {A.z=0; A.n=0;}
indexed_opt(A) ::= INDEXED BY nm(X). {A = X;}
indexed_opt(A) ::= NOT INDEXED.      {A.z=0; A.n=1;}
indexed_opt(A) ::= INDEXED.          {A.z=0; A.n=2;}

%type using_opt {IdList*}
%destructor using_opt {sqlite3IdListDelete(pParse->db, $$);}
using_opt(U) ::= USING LP idlist(L) RP.  {U = L;}
using_opt(U) ::= .                        {U = 0;}

      u8 jointype;      /* Type of join between this table and the previous */
      unsigned notIndexed :1;    /* True if there is a NOT INDEXED clause */
      unsigned isIndexedBy :1;   /* True if there is an INDEXED BY clause */
      unsigned isTabFunc :1;     /* True if table-valued-function syntax */
      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 */
      unsigned useAutoIdx  :1;   /* Use an automatic index if possible */
    } fg;
    int iCursor;      /* The VDBE cursor number used to access this table */
    Expr *pOn;        /* The ON clause of a join */
    IdList *pUsing;   /* The USING clause of a join */
    Bitmask colUsed;  /* Bit N (1<<N) set if column N of pTab is used */
    union {
      char *zIndexedBy;    /* Identifier from "INDEXED BY <zIndex>" clause */

        ** those objects, since there is no opportunity to add schema
        ** indexes on subqueries and views. */
        pNew->rSetup = rLogSize + rSize + 4;
        if( pTab->pSelect==0 && (pTab->tabFlags & TF_Ephemeral)==0 ){
          pNew->rSetup += 24;
        }
        ApplyCostMultiplier(pNew->rSetup, pTab->costMult);
        if( pNew->rSetup<0 ) pNew->rSetup = 0;
        if( pNew->rSetup<0 || pSrc->fg.useAutoIdx ) pNew->rSetup = 0;
        /* TUNING: Each index lookup yields 20 rows in the table.  This
        ** is more than the usual guess of 10 rows, since we have no way
        ** of knowing how selective the index will ultimately be.  It would
        ** not be unreasonable to make this value much larger. */
        pNew->nOut = 43;  assert( 43==sqlite3LogEst(20) );
        pNew->rRun = sqlite3LogEstAdd(rLogSize,pNew->nOut);
        pNew->wsFlags = WHERE_AUTO_INDEX;

        LogEst rUnsorted;                 /* Unsorted cost of (pFrom+pWLoop) */
        i8 isOrdered = pFrom->isOrdered;  /* isOrdered for (pFrom+pWLoop) */
        Bitmask maskNew;                  /* Mask of src visited by (..) */
        Bitmask revMask = 0;              /* Mask of rev-order loops for (..) */

        if( (pWLoop->prereq & ~pFrom->maskLoop)!=0 ) continue;
        if( (pWLoop->maskSelf & pFrom->maskLoop)!=0 ) continue;
        if( (pWLoop->wsFlags & WHERE_AUTO_INDEX)!=0 && pFrom->nRow<10 ){
        if( (pWLoop->wsFlags & WHERE_AUTO_INDEX)!=0
         && (pWInfo->wctrlFlags & WHERE_USE_LIMIT)!=0
         && pWInfo->iLimit<10
        ){
          /* Do not use an automatic index if the this loop is expected
          ** to run less than 2 times. */
          ** to run less than twice due to a LIMIT clause. */
          assert( 10==sqlite3LogEst(2) );
          continue;
        }
        /* At this point, pWLoop is a candidate to be the next loop. 
        ** Compute its cost */
        rUnsorted = sqlite3LogEstAdd(pWLoop->rSetup,pWLoop->rRun + pFrom->nRow);
        rUnsorted = sqlite3LogEstAdd(rUnsorted, pFrom->rUnsorted);