SQLite

    *pDifferentRow = 1;
  }else{
    assert( pCur->skipNext==0 );
    *pDifferentRow = 0;
  }
  return SQLITE_OK;
}

#ifdef SQLITE_ENABLE_CURSOR_HINTS
/*
** Provide hints to the cursor.  The particular hint given (and the type
** and number of the varargs parameters) is determined by the eHintType
** parameter.  See the definitions of the BTREE_HINT_* macros for details.
*/
void sqlite3BtreeCursorHint(BtCursor *pCur, int eHintType, ...){
  /* Used only by system that substitute their own storage engine */
}
#endif

/*
** Provide flag hints to the cursor.
*/
void sqlite3BtreeCursorHintFlags(BtCursor *pCur, unsigned x){
  assert( x==BTREE_SEEK_EQ || x==BTREE_BULKLOAD || x==0 );
  pCur->hints = x;
}


#ifndef SQLITE_OMIT_AUTOVACUUM
/*
** Given a page number of a regular database page, return the page
** number for the pointer-map page that contains the entry for the
** input page number.
**

    }
  }

  pBt->btsFlags &= ~BTS_NO_WAL;
  return rc;
}









#ifdef SQLITE_DEBUG
/*
** Return true if the cursor has a hint specified.  This routine is
** only used from within assert() statements
*/
int sqlite3BtreeCursorHasHint(BtCursor *pCsr, unsigned int mask){
  return (pCsr->hints & mask)!=0;

#define BTREE_TEXT_ENCODING       5
#define BTREE_USER_VERSION        6
#define BTREE_INCR_VACUUM         7
#define BTREE_APPLICATION_ID      8
#define BTREE_DATA_VERSION        15  /* A virtual meta-value */

/*
** Kinds of hints that can be passed into the sqlite3BtreeCursorHint()
** interface.
**
** BTREE_HINT_RANGE  (arguments: Expr*, Mem*)
**
**     The first argument is an Expr* (which is guaranteed to be constant for
**     the lifetime of the cursor) that defines constraints on which rows
**     might be fetched with this cursor.  The Expr* tree may contain
**     TK_REGISTER nodes that refer to values stored in the array of registers
**     passed as the second parameter.  In other words, if Expr.op==TK_REGISTER
**     then the value of the node is the value in Mem[pExpr.iTable].  Any
**     TK_COLUMN node in the expression tree refers to the Expr.iColumn-th
**     column of the b-tree of the cursor.  The Expr tree will not contain
**     any function calls nor subqueries nor references to b-trees other than
**     the cursor being hinted.
**
**     The design of the _RANGE hint is aid b-tree implementations that try
**     to prefetch content from remote machines - to provide those
**     implementations with limits on what needs to be prefetched and thereby
**     reduce network bandwidth.
**
** Note that BTREE_HINT_FLAGS with BTREE_BULKLOAD is the only hint used by
** standard SQLite.  The other hints are provided for extentions that use
** the SQLite parser and code generator but substitute their own storage
** engine.
*/
#define BTREE_HINT_RANGE 0       /* Range constraints on queries */

/*
** Values that may be OR'd together to form the argument to the
** BTREE_HINT_FLAGS hint for sqlite3BtreeCursorHint():
**
** The BTREE_BULKLOAD flag is set on index cursors when the index is going
** to be filled with content that is already in sorted order.
**
** The BTREE_SEEK_EQ flag is set on cursors that will get OP_SeekGE or
** OP_SeekLE opcodes for a range search, but where the range of entries
** selected will all have the same key.  In other words, the cursor will

  int iTable,                          /* Index of root page */
  int wrFlag,                          /* 1 for writing.  0 for read-only */
  struct KeyInfo*,                     /* First argument to compare function */
  BtCursor *pCursor                    /* Space to write cursor structure */
);
int sqlite3BtreeCursorSize(void);
void sqlite3BtreeCursorZero(BtCursor*);
void sqlite3BtreeCursorHintFlags(BtCursor*, unsigned);
#ifdef SQLITE_ENABLE_CURSOR_HINTS
void sqlite3BtreeCursorHint(BtCursor*, int, ...);
#endif

int sqlite3BtreeCloseCursor(BtCursor*);
int sqlite3BtreeMovetoUnpacked(
  BtCursor*,
  UnpackedRecord *pUnKey,
  i64 intKey,
  int bias,

char *sqlite3BtreeIntegrityCheck(Btree*, int *aRoot, int nRoot, int, int*);
struct Pager *sqlite3BtreePager(Btree*);

int sqlite3BtreePutData(BtCursor*, u32 offset, u32 amt, void*);
void sqlite3BtreeIncrblobCursor(BtCursor *);
void sqlite3BtreeClearCursor(BtCursor *);
int sqlite3BtreeSetVersion(Btree *pBt, int iVersion);

#ifdef SQLITE_DEBUG
int sqlite3BtreeCursorHasHint(BtCursor*, unsigned int mask);
#endif
int sqlite3BtreeIsReadonly(Btree *pBt);
int sqlite3HeaderSizeBtree(void);

#ifndef NDEBUG

** is considered a variable but a single-quoted string (ex: 'abc') is
** a constant.
*/
int sqlite3ExprIsConstantOrFunction(Expr *p, u8 isInit){
  assert( isInit==0 || isInit==1 );
  return exprIsConst(p, 4+isInit, 0);
}

#ifdef SQLITE_ENABLE_CURSOR_HINTS
/*
** Walk an expression tree.  Return 1 if the expression contains a
** subquery of some kind.  Return 0 if there are no subqueries.
*/
int sqlite3ExprContainsSubquery(Expr *p){
  Walker w;
  memset(&w, 0, sizeof(w));
  w.eCode = 1;
  w.xExprCallback = sqlite3ExprWalkNoop;
  w.xSelectCallback = selectNodeIsConstant;
  sqlite3WalkExpr(&w, p);
  return w.eCode==0;
}
#endif

/*
** If the expression p codes a constant integer that is small enough
** to fit in a 32-bit integer, return 1 and put the value of the integer
** in *pValue.  If the expression is not an integer or if it is too big
** to fit in a signed 32-bit integer, return 0 and leave *pValue unchanged.
*/

**
** When this routine is the Walker.xExprCallback then expression trees
** are walked without any actions being taken at each node.  Presumably,
** when this routine is used for Walker.xExprCallback then 
** Walker.xSelectCallback is set to do something useful for every 
** subquery in the parser tree.
*/
int sqlite3ExprWalkNoop(Walker *NotUsed, Expr *NotUsed2){
  UNUSED_PARAMETER2(NotUsed, NotUsed2);
  return WRC_Continue;
}

/*
** This routine "expands" a SELECT statement and all of its subqueries.
** For additional information on what it means to "expand" a SELECT
** statement, see the comment on the selectExpand worker callback above.
**
** Expanding a SELECT statement is the first step in processing a
** SELECT statement.  The SELECT statement must be expanded before
** name resolution is performed.
**
** If anything goes wrong, an error message is written into pParse.
** The calling function can detect the problem by looking at pParse->nErr
** and/or pParse->db->mallocFailed.
*/
static void sqlite3SelectExpand(Parse *pParse, Select *pSelect){
  Walker w;
  memset(&w, 0, sizeof(w));
  w.xExprCallback = sqlite3ExprWalkNoop;
  w.pParse = pParse;
  if( pParse->hasCompound ){
    w.xSelectCallback = convertCompoundSelectToSubquery;
    sqlite3WalkSelect(&w, pSelect);
  }
  w.xSelectCallback = selectExpander;
  if( (pSelect->selFlags & SF_MultiValue)==0 ){

** Use this routine after name resolution.
*/
static void sqlite3SelectAddTypeInfo(Parse *pParse, Select *pSelect){
#ifndef SQLITE_OMIT_SUBQUERY
  Walker w;
  memset(&w, 0, sizeof(w));
  w.xSelectCallback2 = selectAddSubqueryTypeInfo;
  w.xExprCallback = sqlite3ExprWalkNoop;
  w.pParse = pParse;
  sqlite3WalkSelect(&w, pSelect);
#endif
}


/*

#define SQLITE_DistinctOpt    0x0020   /* DISTINCT using indexes */
#define SQLITE_CoverIdxScan   0x0040   /* Covering index scans */
#define SQLITE_OrderByIdxJoin 0x0080   /* ORDER BY of joins via index */
#define SQLITE_SubqCoroutine  0x0100   /* Evaluate subqueries as coroutines */
#define SQLITE_Transitive     0x0200   /* Transitive constraints */
#define SQLITE_OmitNoopJoin   0x0400   /* Omit unused tables in joins */
#define SQLITE_Stat34         0x0800   /* Use STAT3 or STAT4 data */
#define SQLITE_CursorHints    0x2000   /* Add OP_CursorHint opcodes */
#define SQLITE_AllOpts        0xffff   /* All optimizations */

/*
** Macros for testing whether or not optimizations are enabled or disabled.
*/
#ifndef SQLITE_OMIT_BUILTIN_TEST
#define OptimizationDisabled(db, mask)  (((db)->dbOptFlags&(mask))!=0)

  u8 eCode;                                 /* A small processing code */
  union {                                   /* Extra data for callback */
    NameContext *pNC;                          /* Naming context */
    int n;                                     /* A counter */
    int iCur;                                  /* A cursor number */
    SrcList *pSrcList;                         /* FROM clause */
    struct SrcCount *pSrcCount;                /* Counting column references */
    struct CCurHint *pCCurHint;                /* Used by codeCursorHint() */
  } u;
};

/* Forward declarations */
int sqlite3WalkExpr(Walker*, Expr*);
int sqlite3WalkExprList(Walker*, ExprList*);
int sqlite3WalkSelect(Walker*, Select*);
int sqlite3WalkSelectExpr(Walker*, Select*);
int sqlite3WalkSelectFrom(Walker*, Select*);
int sqlite3ExprWalkNoop(Walker*, Expr*);

/*
** Return code from the parse-tree walking primitives and their
** callbacks.
*/
#define WRC_Continue    0   /* Continue down into children */
#define WRC_Prune       1   /* Omit children but continue walking siblings */

void sqlite3Savepoint(Parse*, int, Token*);
void sqlite3CloseSavepoints(sqlite3 *);
void sqlite3LeaveMutexAndCloseZombie(sqlite3*);
int sqlite3ExprIsConstant(Expr*);
int sqlite3ExprIsConstantNotJoin(Expr*);
int sqlite3ExprIsConstantOrFunction(Expr*, u8);
int sqlite3ExprIsTableConstant(Expr*,int);
#ifdef SQLITE_ENABLE_CURSOR_HINTS
int sqlite3ExprContainsSubquery(Expr*);
#endif
int sqlite3ExprIsInteger(Expr*, int*);
int sqlite3ExprCanBeNull(const Expr*);
int sqlite3ExprNeedsNoAffinityChange(const Expr*, char);
int sqlite3IsRowid(const char*);
void sqlite3GenerateRowDelete(
    Parse*,Table*,Trigger*,int,int,int,i16,u8,u8,u8,int);
void sqlite3GenerateRowIndexDelete(Parse*, Table*, int, int, int*, int);

#endif

#ifdef SQLITE_ENABLE_8_3_NAMES
  Tcl_SetVar2(interp, "sqlite_options", "8_3_names", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "8_3_names", "0", TCL_GLOBAL_ONLY);
#endif

#ifdef SQLITE_ENABLE_CURSOR_HINTS
  Tcl_SetVar2(interp, "sqlite_options", "cursorhints", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "cursorhints", "0", TCL_GLOBAL_ONLY);
#endif

#ifdef SQLITE_ENABLE_MEMSYS3
  Tcl_SetVar2(interp, "sqlite_options", "mem3", "1", TCL_GLOBAL_ONLY);
#else
  Tcl_SetVar2(interp, "sqlite_options", "mem3", "0", TCL_GLOBAL_ONLY);
#endif

  ** and report database corruption if they were not, but this check has
  ** since moved into the btree layer.  */  
  pCur->isTable = pOp->p4type!=P4_KEYINFO;

open_cursor_set_hints:
  assert( OPFLAG_BULKCSR==BTREE_BULKLOAD );
  assert( OPFLAG_SEEKEQ==BTREE_SEEK_EQ );
  testcase( pOp->p5 & OPFLAG_BULKCSR );
#ifdef SQLITE_ENABLE_CURSOR_HINT
  testcase( pOp->p2 & OPFLAG_SEEKEQ );
#endif
  sqlite3BtreeCursorHintFlags(pCur->pCursor,
                               (pOp->p5 & (OPFLAG_BULKCSR|OPFLAG_SEEKEQ)));
  break;
}

/* Opcode: OpenEphemeral P1 P2 * P4 P5
** Synopsis: nColumn=P2
**
** Open a new cursor P1 to a transient table.

  }
#endif /* SQLITE_DEBUG */
#endif /* SQLITE_OMIT_TRACE */
  if( pOp->p2 ) goto jump_to_p2;
  break;
}

#ifdef SQLITE_ENABLE_CURSOR_HINTS
/* Opcode: CursorHint P1 * * P4 *
**
** Provide a hint to cursor P1 that it only needs to return rows that
** satisfy the Expr in P4.  TK_REGISTER terms in the P4 expression refer
** to values currently held in registers.  TK_COLUMN terms in the P4
** expression refer to columns in the b-tree to which cursor P1 is pointing.
*/
case OP_CursorHint: {
  VdbeCursor *pC;

  assert( pOp->p1>=0 && pOp->p1<p->nCursor );
  assert( pOp->p4type==P4_EXPR );
  pC = p->apCsr[pOp->p1];
  if( pC ){
    sqlite3BtreeCursorHint(pC->pCursor, BTREE_HINT_RANGE, pOp->p4.pExpr, aMem);
  }
  break;
}
#endif /* SQLITE_ENABLE_CURSOR_HINTS */

/* Opcode: Noop * * * * *
**
** Do nothing.  This instruction is often useful as a jump
** destination.
*/
/*

    sqlite3_context *pCtx; /* Used when p4type is P4_FUNCCTX */
    CollSeq *pColl;        /* Used when p4type is P4_COLLSEQ */
    Mem *pMem;             /* Used when p4type is P4_MEM */
    VTable *pVtab;         /* Used when p4type is P4_VTAB */
    KeyInfo *pKeyInfo;     /* Used when p4type is P4_KEYINFO */
    int *ai;               /* Used when p4type is P4_INTARRAY */
    SubProgram *pProgram;  /* Used when p4type is P4_SUBPROGRAM */
#ifdef SQLITE_ENABLE_CURSOR_HINTS
    Expr *pExpr;           /* Used when p4type is P4_EXPR */
#endif
    int (*xAdvance)(BtCursor *, int *);
  } p4;
#ifdef SQLITE_ENABLE_EXPLAIN_COMMENTS
  char *zComment;          /* Comment to improve readability */
#endif
#ifdef VDBE_PROFILE
  u32 cnt;                 /* Number of times this instruction was executed */

*/
#define P4_NOTUSED    0   /* The P4 parameter is not used */
#define P4_DYNAMIC  (-1)  /* Pointer to a string obtained from sqliteMalloc() */
#define P4_STATIC   (-2)  /* Pointer to a static string */
#define P4_COLLSEQ  (-4)  /* P4 is a pointer to a CollSeq structure */
#define P4_FUNCDEF  (-5)  /* P4 is a pointer to a FuncDef structure */
#define P4_KEYINFO  (-6)  /* P4 is a pointer to a KeyInfo structure */
#define P4_EXPR     (-7)  /* P4 is a pointer to an Expr tree */
#define P4_MEM      (-8)  /* P4 is a pointer to a Mem*    structure */
#define P4_TRANSIENT  0   /* P4 is a pointer to a transient string */
#define P4_VTAB     (-10) /* P4 is a pointer to an sqlite3_vtab structure */
#define P4_MPRINTF  (-11) /* P4 is a string obtained from sqlite3_mprintf() */
#define P4_REAL     (-12) /* P4 is a 64-bit floating point value */
#define P4_INT64    (-13) /* P4 is a 64-bit signed integer */
#define P4_INT32    (-14) /* P4 is a 32-bit signed integer */

** The maximum number of times that a statement will try to reparse
** itself before giving up and returning SQLITE_SCHEMA.
*/
#ifndef SQLITE_MAX_SCHEMA_RETRY
# define SQLITE_MAX_SCHEMA_RETRY 50
#endif

/*
** VDBE_DISPLAY_P4 is true or false depending on whether or not the
** "explain" P4 display logic is enabled.
*/
#if !defined(SQLITE_OMIT_EXPLAIN) || !defined(NDEBUG) \
     || defined(VDBE_PROFILE) || defined(SQLITE_DEBUG)
# define VDBE_DISPLAY_P4 1
#else
# define VDBE_DISPLAY_P4 0
#endif

/*
** SQL is translated into a sequence of instructions to be
** executed by a virtual machine.  Each instruction is an instance
** of the following structure.
*/
typedef struct VdbeOp Op;

        sqlite3DbFree(db, p4);
        break;
      }
      case P4_KEYINFO: {
        if( db->pnBytesFreed==0 ) sqlite3KeyInfoUnref((KeyInfo*)p4);
        break;
      }
#ifdef SQLITE_ENABLE_CURSOR_HINTS
      case P4_EXPR: {
        sqlite3ExprDelete(db, (Expr*)p4);
        break;
      }
#endif
      case P4_MPRINTF: {
        if( db->pnBytesFreed==0 ) sqlite3_free(p4);
        break;
      }
      case P4_FUNCDEF: {
        freeEphemeralFunction(db, (FuncDef*)p4);
        break;

    pOp->p4type = P4_INT32;
  }else if( zP4==0 ){
    pOp->p4.p = 0;
    pOp->p4type = P4_NOTUSED;
  }else if( n==P4_KEYINFO ){
    pOp->p4.p = (void*)zP4;
    pOp->p4type = P4_KEYINFO;
#ifdef SQLITE_ENABLE_CURSOR_HINTS
  }else if( n==P4_EXPR ){
    /* Responsibility for deleting the Expr tree is handed over to the
    ** VDBE by this operation.  The caller should have already invoked
    ** sqlite3ExprDup() or whatever other routine is needed to make a 
    ** private copy of the tree. */
    pOp->p4.pExpr = (Expr*)zP4;
    pOp->p4type = P4_EXPR;
#endif
  }else if( n==P4_VTAB ){
    pOp->p4.p = (void*)zP4;
    pOp->p4type = P4_VTAB;
    sqlite3VtabLock((VTable *)zP4);
    assert( ((VTable *)zP4)->db==p->db );
  }else if( n<0 ){
    pOp->p4.p = (void*)zP4;

    zTemp[0] = 0;
    jj = 0;
  }
  return jj;
}
#endif /* SQLITE_DEBUG */

#if VDBE_DISPLAY_P4 && defined(SQLITE_ENABLE_CURSOR_HINTS)
/*
** Translate the P4.pExpr value for an OP_CursorHint opcode into text
** that can be displayed in the P4 column of EXPLAIN output.
*/
static int displayP4Expr(int nTemp, char *zTemp, Expr *pExpr){
  const char *zOp = 0;
  int n;
  switch( pExpr->op ){
    case TK_STRING:
      sqlite3_snprintf(nTemp, zTemp, "%Q", pExpr->u.zToken);
      break;
    case TK_INTEGER:
      sqlite3_snprintf(nTemp, zTemp, "%d", pExpr->u.iValue);
      break;
    case TK_NULL:
      sqlite3_snprintf(nTemp, zTemp, "NULL");
      break;
    case TK_REGISTER: {
      sqlite3_snprintf(nTemp, zTemp, "r[%d]", pExpr->iTable);
      break;
    }
    case TK_COLUMN: {
      if( pExpr->iColumn<0 ){
        sqlite3_snprintf(nTemp, zTemp, "rowid");
      }else{
        sqlite3_snprintf(nTemp, zTemp, "c%d", (int)pExpr->iColumn);
      }
      break;
    }
    case TK_LT:      zOp = "LT";      break;
    case TK_LE:      zOp = "LE";      break;
    case TK_GT:      zOp = "GT";      break;
    case TK_GE:      zOp = "GE";      break;
    case TK_NE:      zOp = "NE";      break;
    case TK_EQ:      zOp = "EQ";      break;
    case TK_IS:      zOp = "IS";      break;
    case TK_ISNOT:   zOp = "ISNOT";   break;
    case TK_AND:     zOp = "AND";     break;
    case TK_OR:      zOp = "OR";      break;
    case TK_PLUS:    zOp = "ADD";     break;
    case TK_STAR:    zOp = "MUL";     break;
    case TK_MINUS:   zOp = "SUB";     break;
    case TK_REM:     zOp = "REM";     break;
    case TK_BITAND:  zOp = "BITAND";  break;
    case TK_BITOR:   zOp = "BITOR";   break;
    case TK_SLASH:   zOp = "DIV";     break;
    case TK_LSHIFT:  zOp = "LSHIFT";  break;
    case TK_RSHIFT:  zOp = "RSHIFT";  break;
    case TK_CONCAT:  zOp = "CONCAT";  break;
    case TK_UMINUS:  zOp = "MINUS";   break;
    case TK_UPLUS:   zOp = "PLUS";    break;
    case TK_BITNOT:  zOp = "BITNOT";  break;
    case TK_NOT:     zOp = "NOT";     break;
    case TK_ISNULL:  zOp = "ISNULL";  break;
    case TK_NOTNULL: zOp = "NOTNULL"; break;

    default:
      sqlite3_snprintf(nTemp, zTemp, "%s", "expr");
      break;
  }

  if( zOp ){
    sqlite3_snprintf(nTemp, zTemp, "%s(", zOp);
    n = sqlite3Strlen30(zTemp);
    n += displayP4Expr(nTemp-n, zTemp+n, pExpr->pLeft);
    if( n<nTemp-1 && pExpr->pRight ){
      zTemp[n++] = ',';
      n += displayP4Expr(nTemp-n, zTemp+n, pExpr->pRight);
    }
    sqlite3_snprintf(nTemp-n, zTemp+n, ")");
  }
  return sqlite3Strlen30(zTemp);
}
#endif /* VDBE_DISPLAY_P4 && defined(SQLITE_ENABLE_CURSOR_HINTS) */


#if VDBE_DISPLAY_P4
/*
** Compute a string that describes the P4 parameter for an opcode.
** Use zTemp for any required temporary buffer space.
*/
static char *displayP4(Op *pOp, char *zTemp, int nTemp){
  char *zP4 = zTemp;
  assert( nTemp>=20 );

        i += n;
      }
      zTemp[i++] = ')';
      zTemp[i] = 0;
      assert( i<nTemp );
      break;
    }
#ifdef SQLITE_ENABLE_CURSOR_HINTS
    case P4_EXPR: {
      displayP4Expr(nTemp, zTemp, pOp->p4.pExpr);
      break;
    }
#endif
    case P4_COLLSEQ: {
      CollSeq *pColl = pOp->p4.pColl;
      sqlite3_snprintf(nTemp, zTemp, "(%.20s)", pColl->zName);
      break;
    }
    case P4_FUNCDEF: {
      FuncDef *pDef = pOp->p4.pFunc;

        zTemp[0] = 0;
      }
    }
  }
  assert( zP4!=0 );
  return zP4;
}
#endif /* VDBE_DISPLAY_P4 */

/*
** Declare to the Vdbe that the BTree object at db->aDb[i] is used.
**
** The prepared statements need to know in advance the complete set of
** attached databases that will be use.  A mask of these databases
** is maintained in p->btreeMask.  The p->lockMask value is the subset of

    pMem->u.i = pOp->p2;                          /* P2 */
    pMem++;

    pMem->flags = MEM_Int;
    pMem->u.i = pOp->p3;                          /* P3 */
    pMem++;

    if( sqlite3VdbeMemClearAndResize(pMem, 100) ){ /* P4 */
      assert( p->db->mallocFailed );
      return SQLITE_ERROR;
    }
    pMem->flags = MEM_Str|MEM_Term;
    zP4 = displayP4(pOp, pMem->z, pMem->szMalloc);
    if( zP4!=pMem->z ){
      sqlite3VdbeMemSetStr(pMem, zP4, -1, SQLITE_UTF8, 0);
    }else{
      assert( pMem->z!=0 );
      pMem->n = sqlite3Strlen30(pMem->z);
      pMem->enc = SQLITE_UTF8;
    }

         && (wctrlFlags & WHERE_OMIT_OPEN_CLOSE)==0 ){
      int op = OP_OpenRead;
      if( pWInfo->eOnePass!=ONEPASS_OFF ){
        op = OP_OpenWrite;
        pWInfo->aiCurOnePass[0] = pTabItem->iCursor;
      };
      sqlite3OpenTable(pParse, pTabItem->iCursor, iDb, pTab, op);

      assert( pTabItem->iCursor==pLevel->iTabCur );
      testcase( pWInfo->eOnePass==ONEPASS_OFF && pTab->nCol==BMS-1 );
      testcase( pWInfo->eOnePass==ONEPASS_OFF && pTab->nCol==BMS );
      if( pWInfo->eOnePass==ONEPASS_OFF && pTab->nCol<BMS && HasRowid(pTab) ){
        Bitmask b = pTabItem->colUsed;
        int n = 0;
        for(; b; b=b>>1, n++){}
        sqlite3VdbeChangeP4(v, sqlite3VdbeCurrentAddr(v)-1, 
                            SQLITE_INT_TO_PTR(n), P4_INT32);
        assert( n<=pTab->nCol );
      }
#ifdef SQLITE_ENABLE_CURSOR_HINTS
      if( pLoop->u.btree.pIndex!=0 ){
        sqlite3VdbeChangeP5(v, OPFLAG_SEEKEQ|bFordelete);
      }else
#endif
      {
        sqlite3VdbeChangeP5(v, bFordelete);
      }
#ifdef SQLITE_ENABLE_COLUMN_USED_MASK
      sqlite3VdbeAddOp4Dup8(v, OP_ColumnsUsed, pTabItem->iCursor, 0, 0,
                            (const u8*)&pTabItem->colUsed, P4_INT64);
#endif
    }else{
      sqlite3TableLock(pParse, iDb, pTab->tnum, 0, pTab->zName);
    }

    assert( pOp->opcode==OP_String8 
            || pTerm->pWC->pWInfo->pParse->db->mallocFailed );
    pOp->p3 = pLevel->iLikeRepCntr;
    pOp->p5 = 1;
  }
}

#ifdef SQLITE_ENABLE_CURSOR_HINTS
/*
** Information is passed from codeCursorHint() down to individual nodes of
** the expression tree (by sqlite3WalkExpr()) using an instance of this
** structure.
*/
struct CCurHint {
  int iTabCur;    /* Cursor for the main table */
  int iIdxCur;    /* Cursor for the index, if pIdx!=0.  Unused otherwise */
  Index *pIdx;    /* The index used to access the table */
};

/*
** This function is called for every node of an expression that is a candidate
** for a cursor hint on an index cursor.  For TK_COLUMN nodes that reference
** the table CCurHint.iTabCur, verify that the same column can be
** accessed through the index.  If it cannot, then set pWalker->eCode to 1.
*/
static int codeCursorHintCheckExpr(Walker *pWalker, Expr *pExpr){
  struct CCurHint *pHint = pWalker->u.pCCurHint;
  assert( pHint->pIdx!=0 );
  if( pExpr->op==TK_COLUMN
   && pExpr->iTable==pHint->iTabCur
   && sqlite3ColumnOfIndex(pHint->pIdx, pExpr->iColumn)<0
  ){
    pWalker->eCode = 1;
  }
  return WRC_Continue;
}


/*
** This function is called on every node of an expression tree used as an
** argument to the OP_CursorHint instruction. If the node is a TK_COLUMN
** that accesses any table other than the one identified by
** CCurHint.iTabCur, then do the following:
**
**   1) allocate a register and code an OP_Column instruction to read 
**      the specified column into the new register, and
**
**   2) transform the expression node to a TK_REGISTER node that reads 
**      from the newly populated register.
**
** Also, if the node is a TK_COLUMN that does access the table idenified
** by pCCurHint.iTabCur, and an index is being used (which we will
** know because CCurHint.pIdx!=0) then transform the TK_COLUMN into
** an access of the index rather than the original table.
*/
static int codeCursorHintFixExpr(Walker *pWalker, Expr *pExpr){
  int rc = WRC_Continue;
  struct CCurHint *pHint = pWalker->u.pCCurHint;
  if( pExpr->op==TK_COLUMN ){
    if( pExpr->iTable!=pHint->iTabCur ){
      Vdbe *v = pWalker->pParse->pVdbe;
      int reg = ++pWalker->pParse->nMem;   /* Register for column value */
      sqlite3ExprCodeGetColumnOfTable(
          v, pExpr->pTab, pExpr->iTable, pExpr->iColumn, reg
      );
      pExpr->op = TK_REGISTER;
      pExpr->iTable = reg;
    }else if( pHint->pIdx!=0 ){
      pExpr->iTable = pHint->iIdxCur;
      pExpr->iColumn = sqlite3ColumnOfIndex(pHint->pIdx, pExpr->iColumn);
      assert( pExpr->iColumn>=0 );
    }
  }else if( pExpr->op==TK_AGG_FUNCTION ){
    /* An aggregate function in the WHERE clause of a query means this must
    ** be a correlated sub-query, and expression pExpr is an aggregate from
    ** the parent context. Do not walk the function arguments in this case.
    **
    ** todo: It should be possible to replace this node with a TK_REGISTER
    ** expression, as the result of the expression must be stored in a 
    ** register at this point. The same holds for TK_AGG_COLUMN nodes. */
    rc = WRC_Prune;
  }
  return rc;
}

/*
** Insert an OP_CursorHint instruction if it is appropriate to do so.
*/
static void codeCursorHint(
  WhereInfo *pWInfo,    /* The where clause */
  WhereLevel *pLevel,   /* Which loop to provide hints for */
  WhereTerm *pEndRange  /* Hint this end-of-scan boundary term if not NULL */
){
  Parse *pParse = pWInfo->pParse;
  sqlite3 *db = pParse->db;
  Vdbe *v = pParse->pVdbe;
  Expr *pExpr = 0;
  WhereLoop *pLoop = pLevel->pWLoop;
  int iCur;
  WhereClause *pWC;
  WhereTerm *pTerm;
  int i, j;
  struct CCurHint sHint;
  Walker sWalker;

  if( OptimizationDisabled(db, SQLITE_CursorHints) ) return;
  iCur = pLevel->iTabCur;
  assert( iCur==pWInfo->pTabList->a[pLevel->iFrom].iCursor );
  sHint.iTabCur = iCur;
  sHint.iIdxCur = pLevel->iIdxCur;
  sHint.pIdx = pLoop->u.btree.pIndex;
  memset(&sWalker, 0, sizeof(sWalker));
  sWalker.pParse = pParse;
  sWalker.u.pCCurHint = &sHint;
  pWC = &pWInfo->sWC;
  for(i=0; i<pWC->nTerm; i++){
    pTerm = &pWC->a[i];
    if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_CODED) ) continue;
    if( pTerm->prereqAll & pLevel->notReady ) continue;
    if( ExprHasProperty(pTerm->pExpr, EP_FromJoin) ) continue;

    /* All terms in pWLoop->aLTerm[] except pEndRange are used to initialize
    ** the cursor.  These terms are not needed as hints for a pure range
    ** scan (that has no == terms) so omit them. */
    if( pLoop->u.btree.nEq==0 && pTerm!=pEndRange ){
      for(j=0; j<pLoop->nLTerm && pLoop->aLTerm[j]!=pTerm; j++){}
      if( j<pLoop->nLTerm ) continue;
    }

    /* No subqueries or non-deterministic functions allowed */
    if( sqlite3ExprContainsSubquery(pTerm->pExpr) ) continue;

    /* For an index scan, make sure referenced columns are actually in
    ** the index. */
    if( sHint.pIdx!=0 ){
      sWalker.eCode = 0;
      sWalker.xExprCallback = codeCursorHintCheckExpr;
      sqlite3WalkExpr(&sWalker, pTerm->pExpr);
      if( sWalker.eCode ) continue;
    }

    /* If we survive all prior tests, that means this term is worth hinting */
    pExpr = sqlite3ExprAnd(db, pExpr, sqlite3ExprDup(db, pTerm->pExpr, 0));
  }
  if( pExpr!=0 ){
    sWalker.xExprCallback = codeCursorHintFixExpr;
    sqlite3WalkExpr(&sWalker, pExpr);
    sqlite3VdbeAddOp4(v, OP_CursorHint, 
                      (sHint.pIdx ? sHint.iIdxCur : sHint.iTabCur), 0, 0,
                      (const char*)pExpr, P4_EXPR);
  }
}
#else
# define codeCursorHint(A,B,C)  /* No-op */
#endif /* SQLITE_ENABLE_CURSOR_HINTS */

/*
** Generate code for the start of the iLevel-th loop in the WHERE clause
** implementation described by pWInfo.
*/
Bitmask sqlite3WhereCodeOneLoopStart(
  WhereInfo *pWInfo,   /* Complete information about the WHERE clause */

    if( pLoop->wsFlags & WHERE_TOP_LIMIT ) pEnd = pLoop->aLTerm[j++];
    assert( pStart!=0 || pEnd!=0 );
    if( bRev ){
      pTerm = pStart;
      pStart = pEnd;
      pEnd = pTerm;
    }
    codeCursorHint(pWInfo, pLevel, pEnd);
    if( pStart ){
      Expr *pX;             /* The expression that defines the start bound */
      int r1, rTemp;        /* Registers for holding the start boundary */

      /* The following constant maps TK_xx codes into corresponding 
      ** seek opcodes.  It depends on a particular ordering of TK_xx
      */

       && pIdx->pTable->aCol[j].notNull==0
      ){
        bSeekPastNull = 1;
      }
    }
    assert( pRangeEnd==0 || (pRangeEnd->wtFlags & TERM_VNULL)==0 );










    /* If we are doing a reverse order scan on an ascending index, or
    ** a forward order scan on a descending index, interchange the 
    ** start and end terms (pRangeStart and pRangeEnd).
    */
    if( (nEq<pIdx->nKeyCol && bRev==(pIdx->aSortOrder[nEq]==SQLITE_SO_ASC))
     || (bRev && pIdx->nKeyCol==nEq)
    ){
      SWAP(WhereTerm *, pRangeEnd, pRangeStart);
      SWAP(u8, bSeekPastNull, bStopAtNull);
    }

    /* Generate code to evaluate all constraint terms using == or IN
    ** and store the values of those terms in an array of registers
    ** starting at regBase.
    */
    codeCursorHint(pWInfo, pLevel, pRangeEnd);
    regBase = codeAllEqualityTerms(pParse,pLevel,bRev,nExtraReg,&zStartAff);
    assert( zStartAff==0 || sqlite3Strlen30(zStartAff)>=nEq );
    if( zStartAff ) cEndAff = zStartAff[nEq];
    addrNxt = pLevel->addrNxt;

    testcase( pRangeStart && (pRangeStart->eOperator & WO_LE)!=0 );
    testcase( pRangeStart && (pRangeStart->eOperator & WO_GE)!=0 );
    testcase( pRangeEnd && (pRangeEnd->eOperator & WO_LE)!=0 );
    testcase( pRangeEnd && (pRangeEnd->eOperator & WO_GE)!=0 );
    startEq = !pRangeStart || pRangeStart->eOperator & (WO_LE|WO_GE);
    endEq =   !pRangeEnd || pRangeEnd->eOperator & (WO_LE|WO_GE);

    static const u8 aStart[] = { OP_Rewind, OP_Last };
    assert( bRev==0 || bRev==1 );
    if( pTabItem->fg.isRecursive ){
      /* Tables marked isRecursive have only a single row that is stored in
      ** a pseudo-cursor.  No need to Rewind or Next such cursors. */
      pLevel->op = OP_Noop;
    }else{
      codeCursorHint(pWInfo, pLevel, 0);
      pLevel->op = aStep[bRev];
      pLevel->p1 = iCur;
      pLevel->p2 = 1 + sqlite3VdbeAddOp2(v, aStart[bRev], iCur, addrBrk);
      VdbeCoverageIf(v, bRev==0);
      VdbeCoverageIf(v, bRev!=0);
      pLevel->p5 = SQLITE_STMTSTATUS_FULLSCAN_STEP;
    }

# 2014 July 15
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    May you do good and not evil.
#    May you find forgiveness for yourself and forgive others.
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.
#

set testdir [file dirname $argv0]
source $testdir/tester.tcl
set testprefix cursorhint

ifcapable !cursorhints {
  finish_test
  return
}

do_execsql_test 1.0 {
  CREATE TABLE t1(a,b,c,d);
  CREATE TABLE t2(x,y,z);
  INSERT INTO t1(a,b) VALUES(10, 15);
  INSERT INTO t1(a,b) VALUES(20, 25);
  INSERT INTO t2(x,y) VALUES('ten', 'fifteen');
  INSERT INTO t2(x,y) VALUES('twenty', 'twentyfive');
  CREATE TABLE t3(id TEXT PRIMARY KEY, a, b, c, d) WITHOUT ROWID;
  INSERT INTO t3(id,a,b,c,d) SELECT rowid, a, b, c, d FROM t1;
  PRAGMA automatic_index = 0;
}

# Run EXPLAIN on $sql.  Return a list of P4 values for all $opcode
# opcodes.
#
proc p4_of_opcode {db opcode sql} {
  set res {}
  $db eval "EXPLAIN $sql" x {
    if {$x(opcode)==$opcode} {lappend res $x(p4)}
  }
  return $res
}

# Run EXPLAIN on $sql.  Return a list of P5 values for all $opcode
# opcodes that contain regexp $comment in their comment
#
proc p5_of_opcode {db opcode comment sql} {
  set res {}
  $db eval "EXPLAIN $sql" x {
    if {$x(opcode)==$opcode && [regexp $comment $x(comment)]} {
      lappend res $x(p5)
    }
  }
  return $res
}

# Verify that when t1 is in the outer loop and t2 is in the inner loop,
# no cursor hints occur for t1 (since it is a full table scan) but that
# each t2 access has a cursor hint based on the current t1.a value.
#
do_test 1.1 {
  p4_of_opcode db CursorHint {
     SELECT * FROM t1 CROSS JOIN t2 WHERE a=x
  }
} {{EQ(r[1],c0)}}
do_test 1.2 {
  p5_of_opcode db OpenRead . {
     SELECT * FROM t1 CROSS JOIN t2 WHERE a=x
  }
} {00 00}

# Do the same test the other way around.
#
do_test 2.1 {
  p4_of_opcode db CursorHint {
     SELECT * FROM t2 CROSS JOIN t1 WHERE a=x
  }
} {{EQ(c0,r[1])}}
do_test 2.2 {
  p5_of_opcode db OpenRead . {
     SELECT * FROM t2 CROSS JOIN t1 WHERE a=x
  }
} {00 00}

# Various expressions captured by CursorHint
#
do_test 3.1 {
  p4_of_opcode db CursorHint {
    SELECT * FROM t1 WHERE a=15 AND c=22 AND rowid!=98
  }
} {AND(AND(EQ(c0,15),EQ(c2,22)),NE(rowid,98))}
do_test 3.2 {
  p4_of_opcode db CursorHint {
    SELECT * FROM t3 WHERE a<15 AND b>22 AND id!=98
  }
} {AND(AND(LT(c1,15),GT(c2,22)),NE(c0,98))}

# Indexed queries
#
do_test 4.1asc {
  db eval {
    CREATE INDEX t1bc ON t1(b,c);
    CREATE INDEX t2yz ON t2(y,z);
  }
  p4_of_opcode db CursorHint {
    SELECT * FROM t1 WHERE b>11 ORDER BY b ASC;
  }
} {}
do_test 4.1desc {
  p4_of_opcode db CursorHint {
    SELECT * FROM t1 WHERE b>11 ORDER BY b DESC;
  }
} {GT(c0,11)}
do_test 4.2 {
  p5_of_opcode db OpenRead . {
    SELECT * FROM t1 WHERE b>11;
  }
} {02 00}
do_test 4.3asc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b<11 ORDER BY b ASC;
  }
} {LT(c0,11)}
do_test 4.3desc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b<11 ORDER BY b DESC;
  }
} {}
do_test 4.4 {
  p5_of_opcode db OpenRead . {
    SELECT c FROM t1 WHERE b<11;
  }
} {00}

do_test 4.5asc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b>=10 AND b<=20 ORDER BY b ASC;
  }
} {LE(c0,20)}
do_test 4.5desc {
  p4_of_opcode db CursorHint {
    SELECT c FROM t1 WHERE b>=10 AND b<=20 ORDER BY b DESC;
  }
} {GE(c0,10)}

# If there are any equality terms used in the constraint, then all terms
# should be hinted.
#
do_test 4.6asc {
  p4_of_opcode db CursorHint {
    SELECT rowid FROM t1 WHERE b=22 AND c>=10 AND c<=20 ORDER BY b,c ASC;
  }
} {AND(AND(EQ(c0,22),GE(c1,10)),LE(c1,20))}
do_test 4.6desc {
  p4_of_opcode db CursorHint {
    SELECT rowid FROM t1 WHERE b=22 AND c>=10 AND c<=20 ORDER BY b,c DESC;
  }
} {AND(AND(EQ(c0,22),GE(c1,10)),LE(c1,20))}

finish_test