select.c

sqlite 嵌入式数据库的源码

      if( rc ){
        goto multi_select_end;
      }


      /* Convert the data in the temporary table into whatever form
      ** it is that we currently need.
      */      
      if( eDest!=priorOp || unionTab!=iParm ){
        int iCont, iBreak, iStart;
        assert( p->pEList );
        if( eDest==SRT_Callback ){
          generateColumnNames(pParse, 0, p->pEList);
        }
        iBreak = sqlite3VdbeMakeLabel(v);
        iCont = sqlite3VdbeMakeLabel(v);
        sqlite3VdbeAddOp(v, OP_Rewind, unionTab, iBreak);
        computeLimitRegisters(pParse, p);
        iStart = sqlite3VdbeCurrentAddr(v);
        rc = selectInnerLoop(pParse, p, p->pEList, unionTab, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak, 0);
        if( rc ){
          rc = 1;
          goto multi_select_end;
        }
        sqlite3VdbeResolveLabel(v, iCont);
        sqlite3VdbeAddOp(v, OP_Next, unionTab, iStart);
        sqlite3VdbeResolveLabel(v, iBreak);
        sqlite3VdbeAddOp(v, OP_Close, unionTab, 0);
      }
      break;
    }
    case TK_INTERSECT: {
      int tab1, tab2;
      int iCont, iBreak, iStart;
      Expr *pLimit, *pOffset;
      int addr;

      /* INTERSECT is different from the others since it requires
      ** two temporary tables.  Hence it has its own case.  Begin
      ** by allocating the tables we will need.
      */
      tab1 = pParse->nTab++;
      tab2 = pParse->nTab++;
      if( p->pOrderBy && matchOrderbyToColumn(pParse,p,p->pOrderBy,tab1,1) ){
        rc = 1;
        goto multi_select_end;
      }

      addr = sqlite3VdbeAddOp(v, OP_OpenTemp, tab1, 0);
      rc = multiSelectOpenTempAddr(p, addr);
      if( rc!=SQLITE_OK ){
        goto multi_select_end;
      }
      assert( nAddr<sizeof(aAddr)/sizeof(aAddr[0]) );
      aAddr[nAddr++] = sqlite3VdbeAddOp(v, OP_SetNumColumns, tab1, 0);
      assert( p->pEList );

      /* Code the SELECTs to our left into temporary table "tab1".
      */
      rc = sqlite3Select(pParse, pPrior, SRT_Union, tab1, 0, 0, 0, aff);
      if( rc ){
        goto multi_select_end;
      }

      /* Code the current SELECT into temporary table "tab2"
      */
      addr = sqlite3VdbeAddOp(v, OP_OpenTemp, tab2, 0);
      rc = multiSelectOpenTempAddr(p, addr);
      if( rc!=SQLITE_OK ){
        goto multi_select_end;
      }
      assert( nAddr<sizeof(aAddr)/sizeof(aAddr[0]) );
      aAddr[nAddr++] = sqlite3VdbeAddOp(v, OP_SetNumColumns, tab2, 0);
      p->pPrior = 0;
      pLimit = p->pLimit;
      p->pLimit = 0;
      pOffset = p->pOffset;
      p->pOffset = 0;
      rc = sqlite3Select(pParse, p, SRT_Union, tab2, 0, 0, 0, aff);
      p->pPrior = pPrior;
      sqlite3ExprDelete(p->pLimit);
      p->pLimit = pLimit;
      p->pOffset = pOffset;
      if( rc ){
        goto multi_select_end;
      }

      /* Generate code to take the intersection of the two temporary
      ** tables.
      */
      assert( p->pEList );
      if( eDest==SRT_Callback ){
        generateColumnNames(pParse, 0, p->pEList);
      }
      iBreak = sqlite3VdbeMakeLabel(v);
      iCont = sqlite3VdbeMakeLabel(v);
      sqlite3VdbeAddOp(v, OP_Rewind, tab1, iBreak);
      computeLimitRegisters(pParse, p);
      iStart = sqlite3VdbeAddOp(v, OP_RowKey, tab1, 0);
      sqlite3VdbeAddOp(v, OP_NotFound, tab2, iCont);
      rc = selectInnerLoop(pParse, p, p->pEList, tab1, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak, 0);
      if( rc ){
        rc = 1;
        goto multi_select_end;
      }
      sqlite3VdbeResolveLabel(v, iCont);
      sqlite3VdbeAddOp(v, OP_Next, tab1, iStart);
      sqlite3VdbeResolveLabel(v, iBreak);
      sqlite3VdbeAddOp(v, OP_Close, tab2, 0);
      sqlite3VdbeAddOp(v, OP_Close, tab1, 0);
      break;
    }
  }

  /* Make sure all SELECTs in the statement have the same number of elements
  ** in their result sets.
  */
  assert( p->pEList && pPrior->pEList );
  if( p->pEList->nExpr!=pPrior->pEList->nExpr ){
    sqlite3ErrorMsg(pParse, "SELECTs to the left and right of %s"
      " do not have the same number of result columns", selectOpName(p->op));
    rc = 1;
    goto multi_select_end;
  }

  /* Set the number of columns in temporary tables
  */
  nCol = p->pEList->nExpr;
  while( nAddr>0 ){
    nAddr--;
    sqlite3VdbeChangeP2(v, aAddr[nAddr], nCol);
  }

  /* Compute collating sequences used by either the ORDER BY clause or
  ** by any temporary tables needed to implement the compound select.
  ** Attach the KeyInfo structure to all temporary tables.  Invoke the
  ** ORDER BY processing if there is an ORDER BY clause.
  **
  ** This section is run by the right-most SELECT statement only.
  ** SELECT statements to the left always skip this part.  The right-most
  ** SELECT might also skip this part if it has no ORDER BY clause and
  ** no temp tables are required.
  */
  if( p->pOrderBy || (pOpenTemp && pOpenTemp->nId>0) ){
    int i;                        /* Loop counter */
    KeyInfo *pKeyInfo;            /* Collating sequence for the result set */

    assert( p->ppOpenTemp == &pOpenTemp );
    pKeyInfo = sqliteMalloc(sizeof(*pKeyInfo)+nCol*sizeof(CollSeq*));
    if( !pKeyInfo ){
      rc = SQLITE_NOMEM;
      goto multi_select_end;
    }

    pKeyInfo->enc = pParse->db->enc;
    pKeyInfo->nField = nCol;

    for(i=0; i<nCol; i++){
      pKeyInfo->aColl[i] = multiSelectCollSeq(pParse, p, i);
      if( !pKeyInfo->aColl[i] ){
        pKeyInfo->aColl[i] = pParse->db->pDfltColl;
      }
    }

    for(i=0; pOpenTemp && i<pOpenTemp->nId; i++){
      int p3type = (i==0?P3_KEYINFO_HANDOFF:P3_KEYINFO);
      int addr = pOpenTemp->a[i].idx;
      sqlite3VdbeChangeP3(v, addr, (char *)pKeyInfo, p3type);
    }

    if( p->pOrderBy ){
      struct ExprList_item *pOrderByTerm = p->pOrderBy->a;
      for(i=0; i<p->pOrderBy->nExpr; i++, pOrderByTerm++){
        Expr *pExpr = pOrderByTerm->pExpr;
        char *zName = pOrderByTerm->zName;
        assert( pExpr->op==TK_COLUMN && pExpr->iColumn<nCol );
        /* assert( !pExpr->pColl ); */
        if( zName ){
          pExpr->pColl = sqlite3LocateCollSeq(pParse, zName, -1);
        }else{
          pExpr->pColl = pKeyInfo->aColl[pExpr->iColumn];
        }
      }
      generateSortTail(pParse, p, v, p->pEList->nExpr, eDest, iParm);
    }

    if( !pOpenTemp ){
      /* This happens for UNION ALL ... ORDER BY */
      sqliteFree(pKeyInfo);
    }
  }

multi_select_end:
  if( pOpenTemp ){
    sqlite3IdListDelete(pOpenTemp);
  }
  p->ppOpenTemp = 0;
  return rc;
}
#endif /* SQLITE_OMIT_COMPOUND_SELECT */

#ifndef SQLITE_OMIT_VIEW
/*
** Scan through the expression pExpr.  Replace every reference to
** a column in table number iTable with a copy of the iColumn-th
** entry in pEList.  (But leave references to the ROWID column 
** unchanged.)
**
** This routine is part of the flattening procedure.  A subquery
** whose result set is defined by pEList appears as entry in the
** FROM clause of a SELECT such that the VDBE cursor assigned to that
** FORM clause entry is iTable.  This routine make the necessary 
** changes to pExpr so that it refers directly to the source table
** of the subquery rather the result set of the subquery.
*/
static void substExprList(ExprList*,int,ExprList*);  /* Forward Decl */
static void substSelect(Select *, int, ExprList *);  /* Forward Decl */
static void substExpr(Expr *pExpr, int iTable, ExprList *pEList){
  if( pExpr==0 ) return;
  if( pExpr->op==TK_COLUMN && pExpr->iTable==iTable ){
    if( pExpr->iColumn<0 ){
      pExpr->op = TK_NULL;
    }else{
      Expr *pNew;
      assert( pEList!=0 && pExpr->iColumn<pEList->nExpr );
      assert( pExpr->pLeft==0 && pExpr->pRight==0 && pExpr->pList==0 );
      pNew = pEList->a[pExpr->iColumn].pExpr;
      assert( pNew!=0 );
      pExpr->op = pNew->op;
      assert( pExpr->pLeft==0 );
      pExpr->pLeft = sqlite3ExprDup(pNew->pLeft);
      assert( pExpr->pRight==0 );
      pExpr->pRight = sqlite3ExprDup(pNew->pRight);
      assert( pExpr->pList==0 );
      pExpr->pList = sqlite3ExprListDup(pNew->pList);
      pExpr->iTable = pNew->iTable;
      pExpr->iColumn = pNew->iColumn;
      pExpr->iAgg = pNew->iAgg;
      sqlite3TokenCopy(&pExpr->token, &pNew->token);
      sqlite3TokenCopy(&pExpr->span, &pNew->span);
      pExpr->pSelect = sqlite3SelectDup(pNew->pSelect);
      pExpr->flags = pNew->flags;
    }
  }else{
    substExpr(pExpr->pLeft, iTable, pEList);
    substExpr(pExpr->pRight, iTable, pEList);
    substSelect(pExpr->pSelect, iTable, pEList);
    substExprList(pExpr->pList, iTable, pEList);
  }
}
static void substExprList(ExprList *pList, int iTable, ExprList *pEList){
  int i;
  if( pList==0 ) return;
  for(i=0; i<pList->nExpr; i++){
    substExpr(pList->a[i].pExpr, iTable, pEList);
  }
}
static void substSelect(Select *p, int iTable, ExprList *pEList){
  if( !p ) return;
  substExprList(p->pEList, iTable, pEList);
  substExprList(p->pGroupBy, iTable, pEList);
  substExprList(p->pOrderBy, iTable, pEList);
  substExpr(p->pHaving, iTable, pEList);
  substExpr(p->pWhere, iTable, pEList);
}
#endif /* !defined(SQLITE_OMIT_VIEW) */

#ifndef SQLITE_OMIT_VIEW
/*
** This routine attempts to flatten subqueries in order to speed
** execution.  It returns 1 if it makes changes and 0 if no flattening
** occurs.
**
** To understand the concept of flattening, consider the following
** query:
**
**     SELECT a FROM (SELECT x+y AS a FROM t1 WHERE z<100) WHERE a>5
**
** The default way of implementing this query is to execute the
** subquery first and store the results in a temporary table, then
** run the outer query on that temporary table.  This requires two
** passes over the data.  Furthermore, because the temporary table
** has no indices, the WHERE clause on the outer query cannot be
** optimized.
**
** This routine attempts to rewrite queries such as the above into
** a single flat select, like this:
**
**     SELECT x+y AS a FROM t1 WHERE z<100 AND a>5
**
** The code generated for this simpification gives the same result
** but only has to scan the data once.  And because indices might 
** exist on the table t1, a complete scan of the data might be
** avoided.
**
** Flattening is only attempted if all of the following are true:
**
**   (1)  The subquery and the outer query do not both use aggregates.
**
**   (2)  The subquery is not an aggregate or the outer query is not a join.
**
**   (3)  The subquery is not the right operand of a left outer join, or
**        the subquery is not itself a join.  (Ticket #306)
**
**   (4)  The subquery is not DISTINCT or the outer query is not a join.
**
**   (5)  The subquery is not DISTINCT or the outer query does not use
**        aggregates.
**
**   (6)  The subquery does not use aggregates or the outer query is not
**        DISTINCT.
**
**   (7)  The subquery has a FROM clause.
**
**   (8)  The subquery does not use LIMIT or the outer query is not a join.
**
**   (9)  The subquery does not use LIMIT or the outer query does not use
**        aggregates.
**
**  (10)  The subquery does not use aggregates or the outer query does not
**        use LIMIT.
**
**  (11)  The subquery and the outer query do not both have ORDER BY clauses.
**
**  (12)  The subquery is not the right term of a LEFT OUTER JOIN or the
**        subquery has no WHERE clause.  (added by ticket #350)
**
** In this routine, the "p" parameter is a pointer to the outer query.
** The subquery is p->pSrc->a[iFrom].  isAgg is true if the outer query
** uses aggregates and subqueryIsAgg is true if the subquery uses aggregates.
**
** If flattening is not attempted, this routine is a no-op and returns 0.
** If flattening is attempted this routine returns 1.
**
** All of the expression analysis must occur on both the outer query and
** the subquery before this routine runs.
*/
static int flattenSubquery(
  Parse *pParse,       /* The parsing context */
  Select *p,           /* The parent or outer SELECT statement */
  int iFrom,           /* Index in p->pSrc->a[] of the inner subquery */
  int isAgg,           /* True if outer SELECT uses aggregate functions */
  int subqueryIsAgg    /* True if the subquery uses aggregate functions */
){
  Select *pSub;       /* The inner query or "subquery" */
  SrcList *pSrc;      /* The FROM clause of the outer query */
  SrcList *pSubSrc;   /* The FROM clause of the subquery */
  ExprList *pList;    /* The result set of the outer query */
  int iParent;        /* VDBE cursor number of the pSub result set temp table */
  int i;              /* Loop counter */
  Expr *pWhere;                    /* The WHERE clause */
  struct SrcList_item *pSubitem;   /* The subquery */

  /* Check to see if flattening is permitted.  Return 0 if not.
  */
  if( p==0 ) return 0;
  pSrc = p->pSrc;
  assert( pSrc && iFrom>=0 && iFrom<pSrc->nSrc );
  pSubitem = &pSrc->a[iFrom];
  pSub = pSubitem->pSelect;
  assert( pSub!=0 );
  if( isAgg && subqueryIsAgg ) return 0;
  if( subqueryIsAgg && pSrc->nSrc>1 ) return 0;
  pSubSrc = pSub->pSrc;
  assert( pSubSrc );
  if( (pSub->pLimit && p->pLimit) || pSub->pOffset || 
      (pSub->pLimit && isAgg) ) return 0;
  if( pSubSrc->nSrc==0 ) return 0;
  if( pSub->isDistinct && (pSrc->nSrc>1 || isAgg) ){
     return 0;
  }
  if( p->isDistinct && subqueryIsAgg ) return 0;
  if( p->pOrderBy && pSub->pOrderBy ) return 0;

  /* Restriction 3:  If the subquery is a join, make sure the subquery is 
  ** not used as the right operand of an outer join.  Examples of why this
  ** is not allowed:
  **
  **         t1 LEFT OUTER JOIN (t2 JOIN t3)
  **
  ** If we flatten the above, we would get
  **
  **         (t1 LEFT OUTER JOIN t2) JOIN t3
  **
  ** which is not at all the same thing.
  */
  if( pSubSrc->nSrc>1 && iFrom>0 && (pSrc->a[iFrom-1].jointype & JT_OUTER)!=0 ){
    return 0;
  }

  /* Restriction 1