SQLite

  return pExpr;
}

/*
** Return the collation sequence for the expression pExpr. If
** there is no defined collating sequence, return NULL.
**
** See also: sqlite3ExprNNCollSeq()
**
** The sqlite3ExprNNCollSeq() works the same exact that it returns the
** default collation if pExpr has no defined collation.
**
** The collating sequence might be determined by a COLLATE operator
** or by the presence of a column with a defined collating sequence.
** COLLATE operators take first precedence.  Left operands take
** precedence over right operands.
*/
CollSeq *sqlite3ExprCollSeq(Parse *pParse, Expr *pExpr){
  sqlite3 *db = pParse->db;

    }
  }
  if( sqlite3CheckCollSeq(pParse, pColl) ){ 
    pColl = 0;
  }
  return pColl;
}

/*
** Return the collation sequence for the expression pExpr. If
** there is no defined collating sequence, return a pointer to the
** defautl collation sequence.
**
** See also: sqlite3ExprCollSeq()
**
** The sqlite3ExprCollSeq() routine works the same except that it
** returns NULL if there is no defined collation.
*/
CollSeq *sqlite3ExprNNCollSeq(Parse *pParse, Expr *pExpr){
  CollSeq *p = sqlite3ExprCollSeq(pParse, pExpr);
  if( p==0 ) p = pParse->db->pDfltColl;
  assert( p!=0 );
  return p;
}

/*
** Return TRUE if the two expressions have equivalent collating sequences.
*/
int sqlite3ExprCollSeqMatch(Parse *pParse, Expr *pE1, Expr *pE2){
  CollSeq *pColl1 = sqlite3ExprNNCollSeq(pParse, pE1);
  CollSeq *pColl2 = sqlite3ExprNNCollSeq(pParse, pE2);
  return sqlite3StrICmp(pColl1->zName, pColl2->zName)==0;
}

/*
** pExpr is an operand of a comparison operator.  aff2 is the
** type affinity of the other operand.  This routine returns the
** type affinity that should be used for the comparison operator.
*/
char sqlite3CompareAffinity(Expr *pExpr, char aff2){

  int i;

  /* Check if pExpr is identical to any GROUP BY term. If so, consider
  ** it constant.  */
  for(i=0; i<pGroupBy->nExpr; i++){
    Expr *p = pGroupBy->a[i].pExpr;
    if( sqlite3ExprCompare(0, pExpr, p, -1)<2 ){
      CollSeq *pColl = sqlite3ExprNNCollSeq(pWalker->pParse, p);
      if( sqlite3_stricmp("BINARY", pColl->zName)==0 ){
        return WRC_Prune;
      }
    }
  }

  /* Check if pExpr is a sub-select. If so, consider it variable. */
  if( ExprHasProperty(pExpr, EP_xIsSelect) ){

  int i;

  nExpr = pList->nExpr;
  pInfo = sqlite3KeyInfoAlloc(db, nExpr-iStart, nExtra+1);
  if( pInfo ){
    assert( sqlite3KeyInfoIsWriteable(pInfo) );
    for(i=iStart, pItem=pList->a+iStart; i<nExpr; i++, pItem++){



      pInfo->aColl[i-iStart] = sqlite3ExprNNCollSeq(pParse, pItem->pExpr);
      pInfo->aSortOrder[i-iStart] = pItem->sortOrder;
    }
  }
  return pInfo;
}

/*

#endif

const char *sqlite3ErrStr(int);
int sqlite3ReadSchema(Parse *pParse);
CollSeq *sqlite3FindCollSeq(sqlite3*,u8 enc, const char*,int);
CollSeq *sqlite3LocateCollSeq(Parse *pParse, const char*zName);
CollSeq *sqlite3ExprCollSeq(Parse *pParse, Expr *pExpr);
CollSeq *sqlite3ExprNNCollSeq(Parse *pParse, Expr *pExpr);
int sqlite3ExprCollSeqMatch(Parse*,Expr*,Expr*);
Expr *sqlite3ExprAddCollateToken(Parse *pParse, Expr*, const Token*, int);
Expr *sqlite3ExprAddCollateString(Parse*,Expr*,const char*);
Expr *sqlite3ExprSkipCollate(Expr*);
int sqlite3CheckCollSeq(Parse *, CollSeq *);
int sqlite3CheckObjectName(Parse *, const char *);
void sqlite3VdbeSetChanges(sqlite3 *, int);
int sqlite3AddInt64(i64*,i64);

  for(i=0; i<pList->nExpr; i++){
    Expr *p = sqlite3ExprSkipCollate(pList->a[i].pExpr);
    if( p->op==TK_COLUMN
     && p->iColumn==pIdx->aiColumn[iCol]
     && p->iTable==iBase
    ){
      CollSeq *pColl = sqlite3ExprNNCollSeq(pParse, pList->a[i].pExpr);
      if( 0==sqlite3StrICmp(pColl->zName, zColl) ){
        return i;
      }
    }
  }

  return -1;
}

        ** optimization, and then only if they are actually used
        ** by the query plan */
        assert( wctrlFlags & WHERE_ORDERBY_LIMIT );
        for(j=0; j<pLoop->nLTerm && pTerm!=pLoop->aLTerm[j]; j++){}
        if( j>=pLoop->nLTerm ) continue;
      }
      if( (pTerm->eOperator&(WO_EQ|WO_IS))!=0 && pOBExpr->iColumn>=0 ){

        if( sqlite3ExprCollSeqMatch(pWInfo->pParse, 


                  pOrderBy->a[i].pExpr, pTerm->pExpr)==0 ){


          continue;
        }
        testcase( pTerm->pExpr->op==TK_IS );
      }
      obSat |= MASKBIT(i);
    }

    if( (pLoop->wsFlags & WHERE_ONEROW)==0 ){
      if( pLoop->wsFlags & WHERE_IPK ){

          }else{
            Expr *pIdxExpr = pIndex->aColExpr->a[j].pExpr;
            if( sqlite3ExprCompareSkip(pOBExpr, pIdxExpr, iCur) ){
              continue;
            }
          }
          if( iColumn!=XN_ROWID ){
            pColl = sqlite3ExprNNCollSeq(pWInfo->pParse, pOrderBy->a[i].pExpr);

            if( sqlite3StrICmp(pColl->zName, pIndex->azColl[j])!=0 ) continue;
          }
          pLoop->u.btree.nIdxCol = j+1;
          isMatch = 1;
          break;
        }
        if( isMatch && (wctrlFlags & WHERE_GROUPBY)==0 ){

** for the LHS anyplace else in the WHERE clause where the LHS column occurs.
** This is an optimization.  No harm comes from returning 0.  But if 1 is
** returned when it should not be, then incorrect answers might result.
*/
static int termIsEquivalence(Parse *pParse, Expr *pExpr){
  char aff1, aff2;
  CollSeq *pColl;

  if( !OptimizationEnabled(pParse->db, SQLITE_Transitive) ) return 0;
  if( pExpr->op!=TK_EQ && pExpr->op!=TK_IS ) return 0;
  if( ExprHasProperty(pExpr, EP_FromJoin) ) return 0;
  aff1 = sqlite3ExprAffinity(pExpr->pLeft);
  aff2 = sqlite3ExprAffinity(pExpr->pRight);
  if( aff1!=aff2
   && (!sqlite3IsNumericAffinity(aff1) || !sqlite3IsNumericAffinity(aff2))
  ){
    return 0;
  }
  pColl = sqlite3BinaryCompareCollSeq(pParse, pExpr->pLeft, pExpr->pRight);
  if( pColl==0 || sqlite3StrICmp(pColl->zName, "BINARY")==0 ) return 1;
  return sqlite3ExprCollSeqMatch(pParse, pExpr->pLeft, pExpr->pRight);




}

/*
** Recursively walk the expressions of a SELECT statement and generate
** a bitmask indicating which tables are used in that expression
** tree.
*/