** Additionally, if pExpr is a simple SQL value and the value is the
** same as that currently bound to variable pVar, non-zero is returned.
** Otherwise, if the values are not the same or if pExpr is not a simple
** SQL value, zero is returned.
*/
static int exprCompareVariable(Parse *pParse, Expr *pVar, Expr *pExpr){
  int res = 0;
  int iVar = pVar->iColumn;
  Expr *p = pExpr;

  while( p->op==TK_UMINUS ) p = p->pLeft;
  if( p->op==TK_NULL  || p->op==TK_INTEGER 
   || p->op==TK_FLOAT || p->op==TK_STRING 
   || p->op==TK_BLOB 
  ){

    sqlite3VdbeSetVarmask(pParse->pVdbe, iVar);
    sqlite3_value *pL;
    pL = sqlite3VdbeGetBoundValue(pParse->pReprepare, iVar, SQLITE_AFF_BLOB);
    if( pL ){
      sqlite3_value *pR = 0;
      sqlite3ValueFromExpr(pParse->db, pExpr, SQLITE_UTF8, SQLITE_AFF_BLOB,&pR);
      assert( pR || pParse->db->mallocFailed );
      if( pR && 0==sqlite3MemCompare(pL, pR, 0) ){
        res = 1;
      }
      sqlite3ValueFree(pR);
      sqlite3ValueFree(pL);
    }else if( p->op==TK_NULL ){
      res = 1;
    }
  }

  return res;
}

/*
** Do a deep comparison of two expression trees.  Return 0 if the two
................................................................................
** returns 2, then you do not really know for certain if the two
** expressions are the same.  But if you get a 0 or 1 return, then you
** can be sure the expressions are the same.  In the places where
** this routine is used, it does not hurt to get an extra 2 - that
** just might result in some slightly slower code.  But returning
** an incorrect 0 or 1 could lead to a malfunction.
**




** Argument pParse should normally be NULL. If it is not NULL and 
** expression pA contains SQL variable references, then the values
** currently bound to those variable references may be compared to
** simple SQL values in pB. See comments above function exprCompareVariable()
** for details.

*/
int sqlite3ExprCompare(Parse *pParse, Expr *pA, Expr *pB, int iTab){
  u32 combinedFlags;
  if( pA==0 || pB==0 ){
    return pB==pA ? 0 : 2;
  }
  if( pParse && pA->op==TK_VARIABLE && exprCompareVariable(pParse, pA, pB) ){
................................................................................
**     pE1: x!=?1      pE2: x IS NOT NULL    Result: true
**     pE1: x IS NULL  pE2: x IS NOT NULL    Result: false
**     pE1: x IS ?2    pE2: x IS NOT NULL    Reuslt: false
**
** When comparing TK_COLUMN nodes between pE1 and pE2, if pE2 has
** Expr.iTable<0 then assume a table number given by iTab.
**





** When in doubt, return false.  Returning true might give a performance
** improvement.  Returning false might cause a performance reduction, but
** it will always give the correct answer and is hence always safe.
*/
int sqlite3ExprImpliesExpr(Parse *pParse, Expr *pE1, Expr *pE2, int iTab){
  if( sqlite3ExprCompare(pParse, pE1, pE2, iTab)==0 ){
    return 1;

** Additionally, if pExpr is a simple SQL value and the value is the
** same as that currently bound to variable pVar, non-zero is returned.
** Otherwise, if the values are not the same or if pExpr is not a simple
** SQL value, zero is returned.
*/
static int exprCompareVariable(Parse *pParse, Expr *pVar, Expr *pExpr){
  int res = 0;
  int iVar;
  sqlite3_value *pL, *pR = 0;
  
  sqlite3ValueFromExpr(pParse->db, pExpr, SQLITE_UTF8, SQLITE_AFF_BLOB, &pR);



  if( pR ){
    iVar = pVar->iColumn;
    sqlite3VdbeSetVarmask(pParse->pVdbe, iVar);

    pL = sqlite3VdbeGetBoundValue(pParse->pReprepare, iVar, SQLITE_AFF_BLOB);




    if( pL && 0==sqlite3MemCompare(pL, pR, 0) ){
      res = 1;
    }
    sqlite3ValueFree(pR);
    sqlite3ValueFree(pL);



  }

  return res;
}

/*
** Do a deep comparison of two expression trees.  Return 0 if the two
................................................................................
** returns 2, then you do not really know for certain if the two
** expressions are the same.  But if you get a 0 or 1 return, then you
** can be sure the expressions are the same.  In the places where
** this routine is used, it does not hurt to get an extra 2 - that
** just might result in some slightly slower code.  But returning
** an incorrect 0 or 1 could lead to a malfunction.
**
** If pParse is not NULL then TK_VARIABLE terms in pA with bindings in
** pParse->pReprepare can be matched against literals in pB.  The 
** pParse->pVdbe->expmask bitmask is updated for each variable referenced.
** If pParse is NULL (the normal case) then any TK_VARIABLE term in 
** Argument pParse should normally be NULL. If it is not NULL and pA or




** pB causes a return value of 2.
*/
int sqlite3ExprCompare(Parse *pParse, Expr *pA, Expr *pB, int iTab){
  u32 combinedFlags;
  if( pA==0 || pB==0 ){
    return pB==pA ? 0 : 2;
  }
  if( pParse && pA->op==TK_VARIABLE && exprCompareVariable(pParse, pA, pB) ){
................................................................................
**     pE1: x!=?1      pE2: x IS NOT NULL    Result: true
**     pE1: x IS NULL  pE2: x IS NOT NULL    Result: false
**     pE1: x IS ?2    pE2: x IS NOT NULL    Reuslt: false
**
** When comparing TK_COLUMN nodes between pE1 and pE2, if pE2 has
** Expr.iTable<0 then assume a table number given by iTab.
**
** If pParse is not NULL, then the values of bound variables in pE1 are 
** compared against literal values in pE2 and pParse->pVdbe->expmask is
** modified to record which bound variables are referenced.  If pParse 
** is NULL, then false will be returned if pE1 contains any bound variables.
**
** When in doubt, return false.  Returning true might give a performance
** improvement.  Returning false might cause a performance reduction, but
** it will always give the correct answer and is hence always safe.
*/
int sqlite3ExprImpliesExpr(Parse *pParse, Expr *pE1, Expr *pE2, int iTab){
  if( sqlite3ExprCompare(pParse, pE1, pE2, iTab)==0 ){
    return 1;