select.c

sqlite-3.4.1,嵌入式数据库.是一个功能强大的开源数据库,给学习和研发以及小型公司的发展带来了全所未有的好处.

*/
static void createSortingIndex(Parse *pParse, Select *p, ExprList *pOrderBy){
  if( pOrderBy ){
    int addr;
    assert( pOrderBy->iECursor==0 );
    pOrderBy->iECursor = pParse->nTab++;
    addr = sqlite3VdbeAddOp(pParse->pVdbe, OP_OpenEphemeral,
                            pOrderBy->iECursor, pOrderBy->nExpr+1);
    assert( p->addrOpenEphm[2] == -1 );
    p->addrOpenEphm[2] = addr;
  }
}

#ifndef SQLITE_OMIT_COMPOUND_SELECT
/*
** Return the appropriate collating sequence for the iCol-th column of
** the result set for the compound-select statement "p".  Return NULL if
** the column has no default collating sequence.
**
** The collating sequence for the compound select is taken from the
** left-most term of the select that has a collating sequence.
*/
static CollSeq *multiSelectCollSeq(Parse *pParse, Select *p, int iCol){
  CollSeq *pRet;
  if( p->pPrior ){
    pRet = multiSelectCollSeq(pParse, p->pPrior, iCol);
  }else{
    pRet = 0;
  }
  if( pRet==0 ){
    pRet = sqlite3ExprCollSeq(pParse, p->pEList->a[iCol].pExpr);
  }
  return pRet;
}
#endif /* SQLITE_OMIT_COMPOUND_SELECT */

#ifndef SQLITE_OMIT_COMPOUND_SELECT
/*
** This routine is called to process a query that is really the union
** or intersection of two or more separate queries.
**
** "p" points to the right-most of the two queries.  the query on the
** left is p->pPrior.  The left query could also be a compound query
** in which case this routine will be called recursively. 
**
** The results of the total query are to be written into a destination
** of type eDest with parameter iParm.
**
** Example 1:  Consider a three-way compound SQL statement.
**
**     SELECT a FROM t1 UNION SELECT b FROM t2 UNION SELECT c FROM t3
**
** This statement is parsed up as follows:
**
**     SELECT c FROM t3
**      |
**      `----->  SELECT b FROM t2
**                |
**                `------>  SELECT a FROM t1
**
** The arrows in the diagram above represent the Select.pPrior pointer.
** So if this routine is called with p equal to the t3 query, then
** pPrior will be the t2 query.  p->op will be TK_UNION in this case.
**
** Notice that because of the way SQLite parses compound SELECTs, the
** individual selects always group from left to right.
*/
static int multiSelect(
  Parse *pParse,        /* Parsing context */
  Select *p,            /* The right-most of SELECTs to be coded */
  int eDest,            /* \___  Store query results as specified */
  int iParm,            /* /     by these two parameters.         */
  char *aff             /* If eDest is SRT_Union, the affinity string */
){
  int rc = SQLITE_OK;   /* Success code from a subroutine */
  Select *pPrior;       /* Another SELECT immediately to our left */
  Vdbe *v;              /* Generate code to this VDBE */
  int nCol;             /* Number of columns in the result set */
  ExprList *pOrderBy;   /* The ORDER BY clause on p */
  int aSetP2[2];        /* Set P2 value of these op to number of columns */
  int nSetP2 = 0;       /* Number of slots in aSetP2[] used */

  /* Make sure there is no ORDER BY or LIMIT clause on prior SELECTs.  Only
  ** the last (right-most) SELECT in the series may have an ORDER BY or LIMIT.
  */
  if( p==0 || p->pPrior==0 ){
    rc = 1;
    goto multi_select_end;
  }
  pPrior = p->pPrior;
  assert( pPrior->pRightmost!=pPrior );
  assert( pPrior->pRightmost==p->pRightmost );
  if( pPrior->pOrderBy ){
    sqlite3ErrorMsg(pParse,"ORDER BY clause should come after %s not before",
      selectOpName(p->op));
    rc = 1;
    goto multi_select_end;
  }
  if( pPrior->pLimit ){
    sqlite3ErrorMsg(pParse,"LIMIT clause should come after %s not before",
      selectOpName(p->op));
    rc = 1;
    goto multi_select_end;
  }

  /* Make sure we have a valid query engine.  If not, create a new one.
  */
  v = sqlite3GetVdbe(pParse);
  if( v==0 ){
    rc = 1;
    goto multi_select_end;
  }

  /* Create the destination temporary table if necessary
  */
  if( eDest==SRT_EphemTab ){
    assert( p->pEList );
    assert( nSetP2<sizeof(aSetP2)/sizeof(aSetP2[0]) );
    aSetP2[nSetP2++] = sqlite3VdbeAddOp(v, OP_OpenEphemeral, iParm, 0);
    eDest = SRT_Table;
  }

  /* Generate code for the left and right SELECT statements.
  */
  pOrderBy = p->pOrderBy;
  switch( p->op ){
    case TK_ALL: {
      if( pOrderBy==0 ){
        int addr = 0;
        assert( !pPrior->pLimit );
        pPrior->pLimit = p->pLimit;
        pPrior->pOffset = p->pOffset;
        rc = sqlite3Select(pParse, pPrior, eDest, iParm, 0, 0, 0, aff);
        p->pLimit = 0;
        p->pOffset = 0;
        if( rc ){
          goto multi_select_end;
        }
        p->pPrior = 0;
        p->iLimit = pPrior->iLimit;
        p->iOffset = pPrior->iOffset;
        if( p->iLimit>=0 ){
          addr = sqlite3VdbeAddOp(v, OP_IfMemZero, p->iLimit, 0);
          VdbeComment((v, "# Jump ahead if LIMIT reached"));
        }
        rc = sqlite3Select(pParse, p, eDest, iParm, 0, 0, 0, aff);
        p->pPrior = pPrior;
        if( rc ){
          goto multi_select_end;
        }
        if( addr ){
          sqlite3VdbeJumpHere(v, addr);
        }
        break;
      }
      /* For UNION ALL ... ORDER BY fall through to the next case */
    }
    case TK_EXCEPT:
    case TK_UNION: {
      int unionTab;    /* Cursor number of the temporary table holding result */
      int op = 0;      /* One of the SRT_ operations to apply to self */
      int priorOp;     /* The SRT_ operation to apply to prior selects */
      Expr *pLimit, *pOffset; /* Saved values of p->nLimit and p->nOffset */
      int addr;

      priorOp = p->op==TK_ALL ? SRT_Table : SRT_Union;
      if( eDest==priorOp && pOrderBy==0 && !p->pLimit && !p->pOffset ){
        /* We can reuse a temporary table generated by a SELECT to our
        ** right.
        */
        unionTab = iParm;
      }else{
        /* We will need to create our own temporary table to hold the
        ** intermediate results.
        */
        unionTab = pParse->nTab++;
        if( pOrderBy && matchOrderbyToColumn(pParse, p, pOrderBy, unionTab,1) ){
          rc = 1;
          goto multi_select_end;
        }
        addr = sqlite3VdbeAddOp(v, OP_OpenEphemeral, unionTab, 0);
        if( priorOp==SRT_Table ){
          assert( nSetP2<sizeof(aSetP2)/sizeof(aSetP2[0]) );
          aSetP2[nSetP2++] = addr;
        }else{
          assert( p->addrOpenEphm[0] == -1 );
          p->addrOpenEphm[0] = addr;
          p->pRightmost->usesEphm = 1;
        }
        createSortingIndex(pParse, p, pOrderBy);
        assert( p->pEList );
      }

      /* Code the SELECT statements to our left
      */
      assert( !pPrior->pOrderBy );
      rc = sqlite3Select(pParse, pPrior, priorOp, unionTab, 0, 0, 0, aff);
      if( rc ){
        goto multi_select_end;
      }

      /* Code the current SELECT statement
      */
      switch( p->op ){
         case TK_EXCEPT:  op = SRT_Except;   break;
         case TK_UNION:   op = SRT_Union;    break;
         case TK_ALL:     op = SRT_Table;    break;
      }
      p->pPrior = 0;
      p->pOrderBy = 0;
      p->disallowOrderBy = pOrderBy!=0;
      pLimit = p->pLimit;
      p->pLimit = 0;
      pOffset = p->pOffset;
      p->pOffset = 0;
      rc = sqlite3Select(pParse, p, op, unionTab, 0, 0, 0, aff);
      /* Query flattening in sqlite3Select() might refill p->pOrderBy.
      ** Be sure to delete p->pOrderBy, therefore, to avoid a memory leak. */
      sqlite3ExprListDelete(p->pOrderBy);
      p->pPrior = pPrior;
      p->pOrderBy = pOrderBy;
      sqlite3ExprDelete(p->pLimit);
      p->pLimit = pLimit;
      p->pOffset = pOffset;
      p->iLimit = -1;
      p->iOffset = -1;
      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 ){
          Select *pFirst = p;
          while( pFirst->pPrior ) pFirst = pFirst->pPrior;
          generateColumnNames(pParse, 0, pFirst->pEList);
        }
        iBreak = sqlite3VdbeMakeLabel(v);
        iCont = sqlite3VdbeMakeLabel(v);
        computeLimitRegisters(pParse, p, iBreak);
        sqlite3VdbeAddOp(v, OP_Rewind, unionTab, iBreak);
        iStart = sqlite3VdbeCurrentAddr(v);
        rc = selectInnerLoop(pParse, p, p->pEList, unionTab, p->pEList->nExpr,
                             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( pOrderBy && matchOrderbyToColumn(pParse,p,pOrderBy,tab1,1) ){
        rc = 1;
        goto multi_select_end;
      }
      createSortingIndex(pParse, p, pOrderBy);

      addr = sqlite3VdbeAddOp(v, OP_OpenEphemeral, tab1, 0);
      assert( p->addrOpenEphm[0] == -1 );
      p->addrOpenEphm[0] = addr;
      p->pRightmost->usesEphm = 1;
      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_OpenEphemeral, tab2, 0);
      assert( p->addrOpenEphm[1] == -1 );
      p->addrOpenEphm[1] = addr;
      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 ){
        Select *pFirst = p;
        while( pFirst->pPrior ) pFirst = pFirst->pPrior;
        generateColumnNames(pParse, 0, pFirst->pEList);
      }
      iBreak = sqlite3VdbeMakeLabel(v);
      iCont = sqlite3VdbeMakeLabel(v);
      computeLimitRegisters(pParse, p, iBreak);
      sqlite3VdbeAddOp(v, OP_Rewind, tab1, iBreak);
      iStart = sqlite3VdbeAddOp(v, OP_RowKey, tab1, 0);
      sqlite3VdbeAddOp(v, OP_NotFound, tab2, iCont);
      rc = selectInnerLoop(pParse, p, p->pEList, tab1, p->pEList->nExpr,
                             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( nSetP2 ){
    sqlite3VdbeChangeP2(v, aSetP2[--nSetP2], 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( pOrderBy || p->usesEphm ){
    int i;                        /* Loop counter */
    KeyInfo *pKeyInfo;            /* Collating sequence for the result set */
    Select *pLoop;                /* For looping through SELECT statements */
    int nKeyCol;                  /* Number of entries in pKeyInfo->aCol[] */
    CollSeq **apColl;             /* For looping through pKeyInfo->aColl[] */
    CollSeq **aCopy;              /* A copy of pKeyInfo->aColl[] */

    assert( p->pRightmost==p );
    nKeyCol = nCol + (pOrderBy ? pOrderBy->nExpr : 0);
    pKeyInfo = sqliteMalloc(sizeof(*pKeyInfo)+nKeyCol*(sizeof(CollSeq*) + 1));
    if( !pKeyInfo ){
      rc = SQLITE_NOMEM;
      goto multi_select_end;
    }

    pKeyInfo->enc = ENC(pParse->db);
    pKeyInfo->nField = nCol;

    for(i=0, apColl=pKeyInfo->aColl; i<nCol; i++, apColl++){
      *apColl = multiSelectCollSeq(pParse, p, i);
      if( 0==*