select.c

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  sqlite3 *db;
  int moreToDo = 1;

  pOrderBy = pSelect->pOrderBy;
  if( pOrderBy==0 ) return 0;
  if( pOrderBy->nExpr>SQLITE_MAX_COLUMN ){
    sqlite3ErrorMsg(pParse, "too many terms in ORDER BY clause");
    return 1;
  }
  db = pParse->db;
  for(i=0; i<pOrderBy->nExpr; i++){
    pOrderBy->a[i].done = 0;
  }
  while( pSelect->pPrior ){
    pSelect = pSelect->pPrior;
  }
  while( pSelect && moreToDo ){
    moreToDo = 0;
    for(i=0; i<pOrderBy->nExpr; i++){
      int iCol;
      Expr *pE, *pDup;
      if( pOrderBy->a[i].done ) continue;
      pE = pOrderBy->a[i].pExpr;
      pDup = sqlite3ExprDup(db, pE);
      if( pDup==0 ){
        return 1;
      }
      iCol = matchOrderByTermToExprList(pParse, pSelect, pDup, i+1, 1, 0);
      sqlite3ExprDelete(pDup);
      if( iCol<0 ){
        return 1;
      }
      pEList = pSelect->pEList;
      if( pEList==0 ){
        return 1;
      }
      if( iCol>pEList->nExpr ){
        sqlite3ErrorMsg(pParse, 
           "%r ORDER BY term out of range - should be "
           "between 1 and %d", i+1, pEList->nExpr);
        return 1;
      }
      if( iCol>0 ){
        pE->op = TK_COLUMN;
        pE->iTable = iTable;
        pE->iAgg = -1;
        pE->iColumn = iCol-1;
        pE->pTab = 0;
        pOrderBy->a[i].done = 1;
      }else{
        moreToDo = 1;
      }
    }
    pSelect = pSelect->pNext;
  }
  for(i=0; i<pOrderBy->nExpr; i++){
    if( pOrderBy->a[i].done==0 ){
      sqlite3ErrorMsg(pParse, "%r ORDER BY term does not match any "
            "column in the result set", i+1);
      return 1;
    }
  }
  return 0;
}

/*
** Get a VDBE for the given parser context.  Create a new one if necessary.
** If an error occurs, return NULL and leave a message in pParse.
*/
Vdbe *sqlite3GetVdbe(Parse *pParse){
  Vdbe *v = pParse->pVdbe;
  if( v==0 ){
    v = pParse->pVdbe = sqlite3VdbeCreate(pParse->db);
  }
  return v;
}


/*
** Compute the iLimit and iOffset fields of the SELECT based on the
** pLimit and pOffset expressions.  pLimit and pOffset hold the expressions
** that appear in the original SQL statement after the LIMIT and OFFSET
** keywords.  Or NULL if those keywords are omitted. iLimit and iOffset 
** are the integer memory register numbers for counters used to compute 
** the limit and offset.  If there is no limit and/or offset, then 
** iLimit and iOffset are negative.
**
** This routine changes the values of iLimit and iOffset only if
** a limit or offset is defined by pLimit and pOffset.  iLimit and
** iOffset should have been preset to appropriate default values
** (usually but not always -1) prior to calling this routine.
** Only if pLimit!=0 or pOffset!=0 do the limit registers get
** redefined.  The UNION ALL operator uses this property to force
** the reuse of the same limit and offset registers across multiple
** SELECT statements.
*/
static void computeLimitRegisters(Parse *pParse, Select *p, int iBreak){
  Vdbe *v = 0;
  int iLimit = 0;
  int iOffset;
  int addr1, addr2;

  /* 
  ** "LIMIT -1" always shows all rows.  There is some
  ** contraversy about what the correct behavior should be.
  ** The current implementation interprets "LIMIT 0" to mean
  ** no rows.
  */
  if( p->pLimit ){
    p->iLimit = iLimit = pParse->nMem;
    pParse->nMem += 2;
    v = sqlite3GetVdbe(pParse);
    if( v==0 ) return;
    sqlite3ExprCode(pParse, p->pLimit);
    sqlite3VdbeAddOp(v, OP_MustBeInt, 0, 0);
    sqlite3VdbeAddOp(v, OP_MemStore, iLimit, 1);
    VdbeComment((v, "# LIMIT counter"));
    sqlite3VdbeAddOp(v, OP_IfMemZero, iLimit, iBreak);
    sqlite3VdbeAddOp(v, OP_MemLoad, iLimit, 0);
  }
  if( p->pOffset ){
    p->iOffset = iOffset = pParse->nMem++;
    v = sqlite3GetVdbe(pParse);
    if( v==0 ) return;
    sqlite3ExprCode(pParse, p->pOffset);
    sqlite3VdbeAddOp(v, OP_MustBeInt, 0, 0);
    sqlite3VdbeAddOp(v, OP_MemStore, iOffset, p->pLimit==0);
    VdbeComment((v, "# OFFSET counter"));
    addr1 = sqlite3VdbeAddOp(v, OP_IfMemPos, iOffset, 0);
    sqlite3VdbeAddOp(v, OP_Pop, 1, 0);
    sqlite3VdbeAddOp(v, OP_Integer, 0, 0);
    sqlite3VdbeJumpHere(v, addr1);
    if( p->pLimit ){
      sqlite3VdbeAddOp(v, OP_Add, 0, 0);
    }
  }
  if( p->pLimit ){
    addr1 = sqlite3VdbeAddOp(v, OP_IfMemPos, iLimit, 0);
    sqlite3VdbeAddOp(v, OP_Pop, 1, 0);
    sqlite3VdbeAddOp(v, OP_MemInt, -1, iLimit+1);
    addr2 = sqlite3VdbeAddOp(v, OP_Goto, 0, 0);
    sqlite3VdbeJumpHere(v, addr1);
    sqlite3VdbeAddOp(v, OP_MemStore, iLimit+1, 1);
    VdbeComment((v, "# LIMIT+OFFSET"));
    sqlite3VdbeJumpHere(v, addr2);
  }
}

/*
** Allocate a virtual index to use for sorting.
*/
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( processCompoundOrderBy(pParse, p, unionTab) ){
          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);
        computeLimitRegist