where.c

sqlite 嵌入式数据库的源码

          case TK_GT: iDirectGt[i] = j;  break;
        }
      }
    }

    /* If we found a term that tests ROWID with == or IN, that term
    ** will be used to locate the rows in the database table.  There
    ** is not need to continue into the code below that looks for
    ** an index.  We will always use the ROWID over an index.
    */
    if( iDirectEq[i]>=0 ){
      loopMask |= mask;
      pLevel->pIdx = 0;
      continue;
    }

    /* Do a search for usable indices.  Leave pBestIdx pointing to
    ** the "best" index.  pBestIdx is left set to NULL if no indices
    ** are usable.
    **
    ** The best index is the one with the highest score.  The score
    ** for the index is determined as follows.  For each of the
    ** left-most terms that is fixed by an equality operator, add
    ** 32 to the score.  The right-most term of the index may be
    ** constrained by an inequality.  Add 4 if for an "x<..." constraint
    ** and add 8 for an "x>..." constraint.  If both constraints
    ** are present, add 12.
    **
    ** If the left-most term of the index uses an IN operator
    ** (ex:  "x IN (...)")  then add 16 to the score.
    **
    ** If an index can be used for sorting, add 2 to the score.
    ** If an index contains all the terms of a table that are ever
    ** used by any expression in the SQL statement, then add 1 to
    ** the score.
    **
    ** This scoring system is designed so that the score can later be
    ** used to determine how the index is used.  If the score&0x1c is 0
    ** then all constraints are equalities.  If score&0x4 is not 0 then
    ** there is an inequality used as a termination key.  (ex: "x<...")
    ** If score&0x8 is not 0 then there is an inequality used as the
    ** start key.  (ex: "x>...").  A score or 0x10 is the special case
    ** of an IN operator constraint.  (ex:  "x IN ...").
    **
    ** The IN operator (as in "<expr> IN (...)") is treated the same as
    ** an equality comparison except that it can only be used on the
    ** left-most column of an index and other terms of the WHERE clause
    ** cannot be used in conjunction with the IN operator to help satisfy
    ** other columns of the index.
    */
    for(pIdx=pTab->pIndex; pIdx; pIdx=pIdx->pNext){
      Bitmask eqMask = 0;  /* Index columns covered by an x=... term */
      Bitmask ltMask = 0;  /* Index columns covered by an x<... term */
      Bitmask gtMask = 0;  /* Index columns covered by an x>... term */
      Bitmask inMask = 0;  /* Index columns covered by an x IN .. term */
      Bitmask m;
      int nEq, score, bRev = 0;

      if( pIdx->nColumn>sizeof(eqMask)*8 ){
        continue;  /* Ignore indices with too many columns to analyze */
      }
      for(pTerm=aExpr, j=0; j<nExpr; j++, pTerm++){
        Expr *pX = pTerm->p;
        CollSeq *pColl = sqlite3ExprCollSeq(pParse, pX->pLeft);
        if( !pColl && pX->pRight ){
          pColl = sqlite3ExprCollSeq(pParse, pX->pRight);
        }
        if( !pColl ){
          pColl = pParse->db->pDfltColl;
        }
        if( pTerm->idxLeft==iCur 
             && (pTerm->prereqRight & loopMask)==pTerm->prereqRight ){
          int iColumn = pX->pLeft->iColumn;
          int k;
          char idxaff = iColumn>=0 ? pIdx->pTable->aCol[iColumn].affinity : 0; 
          for(k=0; k<pIdx->nColumn; k++){
            /* If the collating sequences or affinities don't match, 
            ** ignore this index.  */
            if( pColl!=pIdx->keyInfo.aColl[k] ) continue;
            if( !sqlite3IndexAffinityOk(pX, idxaff) ) continue;
            if( pIdx->aiColumn[k]==iColumn ){
              switch( pX->op ){
                case TK_IN: {
                  if( k==0 ) inMask |= 1;
                  break;
                }
                case TK_EQ: {
                  eqMask |= ((Bitmask)1)<<k;
                  break;
                }
                case TK_LE:
                case TK_LT: {
                  ltMask |= ((Bitmask)1)<<k;
                  break;
                }
                case TK_GE:
                case TK_GT: {
                  gtMask |= ((Bitmask)1)<<k;
                  break;
                }
                default: {
                  /* CANT_HAPPEN */
                  assert( 0 );
                  break;
                }
              }
              break;
            }
          }
        }
      }

      /* The following loop ends with nEq set to the number of columns
      ** on the left of the index with == constraints.
      */
      for(nEq=0; nEq<pIdx->nColumn; nEq++){
        m = (((Bitmask)1)<<(nEq+1))-1;
        if( (m & eqMask)!=m ) break;
      }

      /* Begin assemblying the score
      */
      score = nEq*32;   /* Base score is 32 times number of == constraints */
      m = ((Bitmask)1)<<nEq;
      if( m & ltMask ) score+=4;    /* Increase score for a < constraint */
      if( m & gtMask ) score+=8;    /* Increase score for a > constraint */
      if( score==0 && inMask ) score = 16; /* Default score for IN constraint */

      /* Give bonus points if this index can be used for sorting
      */
      if( i==0 && score!=16 && ppOrderBy && *ppOrderBy ){
        int base = pTabList->a[0].iCursor;
        if( isSortingIndex(pParse, pIdx, pTab, base, *ppOrderBy, nEq, &bRev) ){
          score += 2;
        }
      }

      /* Check to see if we can get away with using just the index without
      ** ever reading the table.  If that is the case, then add one bonus
      ** point to the score.
      */
      if( score && pTabItem->colUsed < (((Bitmask)1)<<(BMS-1)) ){
        for(m=0, j=0; j<pIdx->nColumn; j++){
          int x = pIdx->aiColumn[j];
          if( x<BMS-1 ){
            m |= ((Bitmask)1)<<x;
          }
        }
        if( (pTabItem->colUsed & m)==pTabItem->colUsed ){
          score++;
        }
      }

      /* If the score for this index is the best we have seen so far, then
      ** save it
      */
      if( score>bestScore ){
        pBestIdx = pIdx;
        bestScore = score;
        bestRev = bRev;
      }
    }
    pLevel->pIdx = pBestIdx;
    pLevel->score = bestScore;
    pLevel->bRev = bestRev;
    loopMask |= mask;
    if( pBestIdx ){
      pLevel->iIdxCur = pParse->nTab++;
    }
  }

  /* Check to see if the ORDER BY clause is or can be satisfied by the
  ** use of an index on the first table.
  */
  if( ppOrderBy && *ppOrderBy && pTabList->nSrc>0 ){
    Index *pIdx;             /* Index derived from the WHERE clause */
    Table *pTab;             /* Left-most table in the FROM clause */
    int bRev = 0;            /* True to reverse the output order */
    int iCur;                /* Btree-cursor that will be used by pTab */
    WhereLevel *pLevel0 = &pWInfo->a[0];

    pTab = pTabList->a[0].pTab;
    pIdx = pLevel0->pIdx;
    iCur = pTabList->a[0].iCursor;
    if( pIdx==0 && sortableByRowid(iCur, *ppOrderBy, &bRev) ){
      /* The ORDER BY clause specifies ROWID order, which is what we
      ** were going to be doing anyway...
      */
      *ppOrderBy = 0;
      pLevel0->bRev = bRev;
    }else if( pLevel0->score==16 ){
      /* If there is already an IN index on the left-most table,
      ** it will not give the correct sort order.
      ** So, pretend that no suitable index is found.
      */
    }else if( iDirectEq[0]>=0 || iDirectLt[0]>=0 || iDirectGt[0]>=0 ){
      /* If the left-most column is accessed using its ROWID, then do
      ** not try to sort by index.  But do delete the ORDER BY clause
      ** if it is redundant.
      */
    }else if( (pLevel0->score&2)!=0 ){
      /* The index that was selected for searching will cause rows to
      ** appear in sorted order.
      */
      *ppOrderBy = 0;
    }
  }

  /* Open all tables in the pTabList and any indices selected for
  ** searching those tables.
  */
  sqlite3CodeVerifySchema(pParse, -1); /* Insert the cookie verifier Goto */
  pLevel = pWInfo->a;
  for(i=0, pTabItem=pTabList->a; i<pTabList->nSrc; i++, pTabItem++, pLevel++){
    Table *pTab;
    Index *pIx;
    int iIdxCur = pLevel->iIdxCur;

    pTab = pTabItem->pTab;
    if( pTab->isTransient || pTab->pSelect ) continue;
    if( (pLevel->score & 1)==0 ){
      sqlite3OpenTableForReading(v, pTabItem->iCursor, pTab);
    }
    pLevel->iTabCur = pTabItem->iCursor;
    if( (pIx = pLevel->pIdx)!=0 ){
      sqlite3VdbeAddOp(v, OP_Integer, pIx->iDb, 0);
      sqlite3VdbeOp3(v, OP_OpenRead, iIdxCur, pIx->tnum,
                     (char*)&pIx->keyInfo, P3_KEYINFO);
    }
    if( (pLevel->score & 1)!=0 ){
      sqlite3VdbeAddOp(v, OP_SetNumColumns, iIdxCur, pIx->nColumn+1);
    }
    sqlite3CodeVerifySchema(pParse, pTab->iDb);
  }
  pWInfo->iTop = sqlite3VdbeCurrentAddr(v);

  /* Generate the code to do the search
  */
  loopMask = 0;
  pLevel = pWInfo->a;
  pTabItem = pTabList->a;
  for(i=0; i<pTabList->nSrc; i++, pTabItem++, pLevel++){
    int j, k;
    int iCur = pTabItem->iCursor;  /* The VDBE cursor for the table */
    Index *pIdx;       /* The index we will be using */
    int iIdxCur;       /* The VDBE cursor for the index */
    int omitTable;     /* True if we use the index only */

    pIdx = pLevel->pIdx;
    iIdxCur = pLevel->iIdxCur;
    pLevel->inOp = OP_Noop;

    /* Check to see if it is appropriate to omit the use of the table
    ** here and use its index instead.
    */
    omitTable = (pLevel->score&1)!=0;

    /* If this is the right table of a LEFT OUTER JOIN, allocate and
    ** initialize a memory cell that records if this table matches any
    ** row of the left table of the join.
    */
    if( i>0 && (pTabList->a[i-1].jointype & JT_LEFT)!=0 ){
      if( !pParse->nMem ) pParse->nMem++;
      pLevel->iLeftJoin = pParse->nMem++;
      sqlite3VdbeAddOp(v, OP_Null, 0, 0);
      sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iLeftJoin, 1);
      VdbeComment((v, "# init LEFT JOIN no-match flag"));
    }

    if( i<ARRAYSIZE(iDirectEq) && (k = iDirectEq[i])>=0 ){
      /* Case 1:  We can directly reference a single row using an
      **          equality comparison against the ROWID field.  Or
      **          we reference multiple rows using a "rowid IN (...)"
      **          construct.
      */
      assert( k<nExpr );
      pTerm = &aExpr[k];
      assert( pTerm->p!=0 );
      assert( pTerm->idxLeft==iCur );
      assert( omitTable==0 );
      brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
      codeEqualityTerm(pParse, pTerm, brk, pLevel);
      cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
      sqlite3VdbeAddOp(v, OP_MustBeInt, 1, brk);
      sqlite3VdbeAddOp(v, OP_NotExists, iCur, brk);
      VdbeComment((v, "pk"));
      pLevel->op = OP_Noop;
    }else if( pIdx!=0 && pLevel->score>3 && (pLevel->score&0x0c)==0 ){
      /* Case 2:  There is an index and all terms of the WHERE clause that
      **          refer to the index using the "==" or "IN" operators.
      */
      int start;
      int nColumn = (pLevel->score+16)/32;
      brk = pLevel->brk = sqlite3VdbeMakeLabel(v);

      /* For each column of the index, find the term of the WHERE clause that
      ** constraints that column.  If the WHERE clause term is X=expr, then
      ** evaluation expr and leave the result on the stack */
      for(j=0; j<nColumn; j++){
        for(pTerm=aExpr, k=0; k<nExpr; k++, pTerm++){
          Expr *pX = pTerm->p;
          if( pX==0 ) continue;
          if( pTerm->idxLeft==iCur
             && (pTerm->prereqRight & loopMask)==pTerm->prereqRight 
             && pX->pLeft->iColumn==pIdx->aiColumn[j]
             && (pX->op==TK_EQ || pX->op==TK_IN)
          ){
            char idxaff = pIdx->pTable->aCol[pX->pLeft->iColumn].affinity;
            if( sqlite3IndexAffinityOk(pX, idxaff) ){
              codeEqualityTerm(pParse, pTerm, brk, pLevel);
              break;
            }
          }
        }
      }
      pLevel->iMem = pParse->nMem++;
      cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
      buildIndexProbe(v, nColumn, brk, pIdx);
      sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem, 0);

      /* Generate code (1) to move to the first matching element of the table.
      ** Then generate code (2) that jumps to "brk" after the cursor is past
      ** the last matching element of the table.  The code (1) is executed
      ** once to initialize the search, the code (2) is executed before each
      ** iteration of the scan to see if the scan has finished. */
      if( pLevel->bRev ){
        /* Scan in reverse order */
        sqlite3VdbeAddOp(v, OP_MoveLe, iIdxCur, brk);
        start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        sqlite3VdbeAddOp(v, OP_IdxLT, iIdxCur, brk);
        pLevel->op = OP_Prev;
      }else{
        /* Scan in the forward order */
        sqlite3VdbeAddOp(v, OP_MoveGe, iIdxCur, brk);
        start = sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem, 0);
        sqlite3VdbeOp3(v, OP_IdxGE, iIdxCur, brk, "+", P3_STATIC);
        pLevel->op = OP_Next;
      }
      sqlite3VdbeAddOp(v, OP_RowKey, iIdxCur, 0);
      sqlite3VdbeAddOp(v, OP_IdxIsNull, nColumn, cont);
      if( !omitTable ){
        sqlite3VdbeAddOp(v, OP_IdxRowid, iIdxCur, 0);
        sqlite3VdbeAddOp(v, OP_MoveGe, iCur, 0);
      }
      pLevel->p1 = iIdxCur;
      pLevel->p2 = start;
    }else if( i<ARRAYSIZE(iDirectLt) && (iDirectLt[i]>=0 || iDirectGt[i]>=0) ){
      /* Case 3:  We have an inequality comparison against the ROWID field.
      */
      int testOp = OP_Noop;
      int start;
      int bRev = pLevel->bRev;

      assert( omitTable==0 );
      brk = pLevel->brk = sqlite3VdbeMakeLabel(v);
      cont = pLevel->cont = sqlite3VdbeMakeLabel(v);
      if( bRev ){
        int t = iDirectGt[i];
        iDirectGt[i] = iDirectLt[i];
        iDirectLt[i] = t;