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Comment:Fix the LIMIT clause so that it applies to the entire query in a compound query. Prior to this change LIMITs on compound queries did not work at all. Ticket #393. (CVS 1058)
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Timelines: family | ancestors | descendants | both | trunk
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SHA1: 543479e3aed77976a0c689cf40811bf88353f706
User & Date: drh 2003-07-20 01:16:47
Context
2003-07-22
00:39
Make sure temporary file names in windows have a full 15 characters of random text at the end. (CVS 1059) check-in: 6ccb92b1 user: drh tags: trunk
2003-07-20
01:16
Fix the LIMIT clause so that it applies to the entire query in a compound query. Prior to this change LIMITs on compound queries did not work at all. Ticket #393. (CVS 1058) check-in: 543479e3 user: drh tags: trunk
2003-07-19
00:44
Make sure the min() and max() optimizer works correctly when there is a LIMIT clause. Ticket #396. (CVS 1057) check-in: c35e5071 user: drh tags: trunk
Changes
Hide Diffs Unified Diffs Ignore Whitespace Patch

Changes to src/expr.c.

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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains routines used for analyzing expressions and
** for generating VDBE code that evaluates expressions in SQLite.
**
** $Id: expr.c,v 1.96 2003/05/31 16:21:12 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>

/*
** Construct a new expression node and return a pointer to it.  Memory
** for this node is obtained from sqliteMalloc().  The calling function
................................................................................
  pNew->pHaving = sqliteExprDup(p->pHaving);
  pNew->pOrderBy = sqliteExprListDup(p->pOrderBy);
  pNew->op = p->op;
  pNew->pPrior = sqliteSelectDup(p->pPrior);
  pNew->nLimit = p->nLimit;
  pNew->nOffset = p->nOffset;
  pNew->zSelect = 0;


  return pNew;
}


/*
** Add a new element to the end of an expression list.  If pList is
** initially NULL, then create a new expression list.







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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains routines used for analyzing expressions and
** for generating VDBE code that evaluates expressions in SQLite.
**
** $Id: expr.c,v 1.97 2003/07/20 01:16:47 drh Exp $
*/
#include "sqliteInt.h"
#include <ctype.h>

/*
** Construct a new expression node and return a pointer to it.  Memory
** for this node is obtained from sqliteMalloc().  The calling function
................................................................................
  pNew->pHaving = sqliteExprDup(p->pHaving);
  pNew->pOrderBy = sqliteExprListDup(p->pOrderBy);
  pNew->op = p->op;
  pNew->pPrior = sqliteSelectDup(p->pPrior);
  pNew->nLimit = p->nLimit;
  pNew->nOffset = p->nOffset;
  pNew->zSelect = 0;
  pNew->iLimit = -1;
  pNew->iOffset = -1;
  return pNew;
}


/*
** Add a new element to the end of an expression list.  If pList is
** initially NULL, then create a new expression list.

Changes to src/select.c.

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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.144 2003/07/19 00:44:14 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.
................................................................................
    pNew->pGroupBy = pGroupBy;
    pNew->pHaving = pHaving;
    pNew->pOrderBy = pOrderBy;
    pNew->isDistinct = isDistinct;
    pNew->op = TK_SELECT;
    pNew->nLimit = nLimit;
    pNew->nOffset = nOffset;


  }
  return pNew;
}

/*
** Given 1 to 3 identifiers preceeding the JOIN keyword, determine the
** type of join.  Return an integer constant that expresses that type
................................................................................
  if( v==0 ) return 0;
  assert( pEList!=0 );

  /* If there was a LIMIT clause on the SELECT statement, then do the check
  ** to see if this row should be output.
  */
  if( pOrderBy==0 ){
    if( p->nOffset>0 ){
      int addr = sqliteVdbeCurrentAddr(v);
      sqliteVdbeAddOp(v, OP_MemIncr, p->nOffset, addr+2);
      sqliteVdbeAddOp(v, OP_Goto, 0, iContinue);
    }
    if( p->nLimit>=0 ){
      sqliteVdbeAddOp(v, OP_MemIncr, p->nLimit, iBreak);
    }
  }

  /* Pull the requested columns.
  */
  if( nColumn>0 ){
    for(i=0; i<nColumn; i++){
................................................................................
  int iParm        /* Optional parameter associated with eDest */
){
  int end = sqliteVdbeMakeLabel(v);
  int addr;
  if( eDest==SRT_Sorter ) return;
  sqliteVdbeAddOp(v, OP_Sort, 0, 0);
  addr = sqliteVdbeAddOp(v, OP_SortNext, 0, end);
  if( p->nOffset>0 ){
    sqliteVdbeAddOp(v, OP_MemIncr, p->nOffset, addr+4);
    sqliteVdbeAddOp(v, OP_Pop, 1, 0);
    sqliteVdbeAddOp(v, OP_Goto, 0, addr);
  }
  if( p->nLimit>=0 ){
    sqliteVdbeAddOp(v, OP_MemIncr, p->nLimit, end);
  }
  switch( eDest ){
    case SRT_Callback: {
      sqliteVdbeAddOp(v, OP_SortCallback, nColumn, 0);
      break;
    }
    case SRT_Table:
................................................................................
    if( pE->dataType==SQLITE_SO_NUM ) continue;
    assert( pE->iColumn>=0 );
    if( pEList->nExpr>pE->iColumn ){
      pE->dataType = sqliteExprType(pEList->a[pE->iColumn].pExpr);
    }
  }
}















































/*
** 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
................................................................................
** individual selects always group from left to right.
*/
static int multiSelect(Parse *pParse, Select *p, int eDest, int iParm){
  int rc;             /* Success code from a subroutine */
  Select *pPrior;     /* Another SELECT immediately to our left */
  Vdbe *v;            /* Generate code to this VDBE */

  /* Make sure there is no ORDER BY clause on prior SELECTs.  Only the 
  ** last SELECT in the series may have an ORDER BY.
  */
  if( p==0 || p->pPrior==0 ) return 1;
  pPrior = p->pPrior;
  if( pPrior->pOrderBy ){
    sqliteErrorMsg(pParse,"ORDER BY clause should come after %s not before",
      selectOpName(p->op));
    return 1;





  }

  /* Make sure we have a valid query engine.  If not, create a new one.
  */
  v = sqliteGetVdbe(pParse);
  if( v==0 ) return 1;

................................................................................
  }

  /* Generate code for the left and right SELECT statements.
  */
  switch( p->op ){
    case TK_ALL: {
      if( p->pOrderBy==0 ){


        rc = sqliteSelect(pParse, pPrior, eDest, iParm, 0, 0, 0);
        if( rc ) return rc;
        p->pPrior = 0;




        rc = sqliteSelect(pParse, p, eDest, iParm, 0, 0, 0);
        p->pPrior = pPrior;
        if( rc ) return rc;
        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;          /* One of the SRT_ operations to apply to self */
      int priorOp;     /* The SRT_ operation to apply to prior selects */

      ExprList *pOrderBy;  /* The ORDER BY clause for the right SELECT */

      priorOp = p->op==TK_ALL ? SRT_Table : SRT_Union;
      if( eDest==priorOp && p->pOrderBy==0 ){
        /* 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.
................................................................................
         case TK_EXCEPT:  op = SRT_Except;   break;
         case TK_UNION:   op = SRT_Union;    break;
         case TK_ALL:     op = SRT_Table;    break;
      }
      p->pPrior = 0;
      pOrderBy = p->pOrderBy;
      p->pOrderBy = 0;




      rc = sqliteSelect(pParse, p, op, unionTab, 0, 0, 0);
      p->pPrior = pPrior;
      p->pOrderBy = pOrderBy;


      if( rc ) return rc;

      /* 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;
................................................................................
        if( eDest==SRT_Callback ){
          generateColumnNames(pParse, 0, p->pEList);
          generateColumnTypes(pParse, p->pSrc, p->pEList);
        }
        iBreak = sqliteVdbeMakeLabel(v);
        iCont = sqliteVdbeMakeLabel(v);
        sqliteVdbeAddOp(v, OP_Rewind, unionTab, iBreak);

        iStart = sqliteVdbeCurrentAddr(v);
        multiSelectSortOrder(p, p->pOrderBy);
        rc = selectInnerLoop(pParse, p, p->pEList, unionTab, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak);
        if( rc ) return 1;
        sqliteVdbeResolveLabel(v, iCont);
................................................................................
        }
      }
      break;
    }
    case TK_INTERSECT: {
      int tab1, tab2;
      int iCont, iBreak, iStart;


      /* 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( rc ) return rc;

      /* Code the current SELECT into temporary table "tab2"
      */
      sqliteVdbeAddOp(v, OP_OpenTemp, tab2, 1);
      sqliteVdbeAddOp(v, OP_KeyAsData, tab2, 1);
      p->pPrior = 0;




      rc = sqliteSelect(pParse, p, SRT_Union, tab2, 0, 0, 0);
      p->pPrior = pPrior;


      if( rc ) return rc;

      /* Generate code to take the intersection of the two temporary
      ** tables.
      */
      assert( p->pEList );
      if( eDest==SRT_Callback ){
        generateColumnNames(pParse, 0, p->pEList);
        generateColumnTypes(pParse, p->pSrc, p->pEList);
      }
      iBreak = sqliteVdbeMakeLabel(v);
      iCont = sqliteVdbeMakeLabel(v);
      sqliteVdbeAddOp(v, OP_Rewind, tab1, iBreak);

      iStart = sqliteVdbeAddOp(v, OP_FullKey, tab1, 0);
      sqliteVdbeAddOp(v, OP_NotFound, tab2, iCont);
      multiSelectSortOrder(p, p->pOrderBy);
      rc = selectInnerLoop(pParse, p, p->pEList, tab1, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak);
      if( rc ) return 1;
................................................................................
  /* Generating code to find the min or the max.  Basically all we have
  ** to do is find the first or the last entry in the chosen index.  If
  ** the min() or max() is on the INTEGER PRIMARY KEY, then find the first
  ** or last entry in the main table.
  */
  sqliteCodeVerifySchema(pParse, pTab->iDb);
  base = p->pSrc->a[0].iCursor;

  sqliteVdbeAddOp(v, OP_Integer, pTab->iDb, 0);
  sqliteVdbeAddOp(v, OP_OpenRead, base, pTab->tnum);
  sqliteVdbeChangeP3(v, -1, pTab->zName, P3_STATIC);
  cont = sqliteVdbeMakeLabel(v);
  if( pIdx==0 ){
    sqliteVdbeAddOp(v, seekOp, base, 0);
  }else{
................................................................................
  /* Identify column names if we will be using them in a callback.  This
  ** step is skipped if the output is going to some other destination.
  */
  if( eDest==SRT_Callback ){
    generateColumnNames(pParse, pTabList, pEList);
  }

  /* Set the limiter.
  **
  ** The phrase "LIMIT 0" means all rows are shown, not zero rows.
  ** If the comparison is p->nLimit<=0 then "LIMIT 0" shows
  ** all rows.  It is the same as no limit. If the comparision is
  ** p->nLimit<0 then "LIMIT 0" show no rows at all.
  ** "LIMIT -1" always shows all rows.  There is some
  ** contraversy about what the correct behavior should be.
  **
  ** Note that up until this point, the nLimit and nOffset hold
  ** the numeric values of the limit and offset that appeared in
  ** the original SQL.  After this code, the nLimit and nOffset hold
  ** the register number of counters used to track the limit and
  ** offset.
  */
  if( p->nLimit<0 ){
    p->nLimit = -1;
  }else{
    int iMem = pParse->nMem++;
    sqliteVdbeAddOp(v, OP_Integer, -p->nLimit, 0);
    sqliteVdbeAddOp(v, OP_MemStore, iMem, 1);
    p->nLimit = iMem;
  }
  if( p->nOffset<=0 ){
    p->nOffset = 0;
  }else{
    int iMem = pParse->nMem++;
    if( iMem==0 ) iMem = pParse->nMem++;
    sqliteVdbeAddOp(v, OP_Integer, -p->nOffset, 0);
    sqliteVdbeAddOp(v, OP_MemStore, iMem, 1);
    p->nOffset = iMem;
  }

  /* Check for the special case of a min() or max() function by itself
  ** in the result set.
  */
  if( simpleMinMaxQuery(pParse, p, eDest, iParm) ){
    rc = 0;
    goto select_end;
  }
................................................................................
  */
  if( pParent && pParentAgg &&
      flattenSubquery(pParse, pParent, parentTab, *pParentAgg, isAgg) ){
    if( isAgg ) *pParentAgg = 1;
    return rc;
  }





  /* Identify column types if we will be using a callback.  This
  ** step is skipped if the output is going to a destination other
  ** than a callback.
  **
  ** We have to do this separately from the creation of column names
  ** above because if the pTabList contains views then they will not
  ** have been resolved and we will not know the column types until







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**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** This file contains C code routines that are called by the parser
** to handle SELECT statements in SQLite.
**
** $Id: select.c,v 1.145 2003/07/20 01:16:47 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.
................................................................................
    pNew->pGroupBy = pGroupBy;
    pNew->pHaving = pHaving;
    pNew->pOrderBy = pOrderBy;
    pNew->isDistinct = isDistinct;
    pNew->op = TK_SELECT;
    pNew->nLimit = nLimit;
    pNew->nOffset = nOffset;
    pNew->iLimit = -1;
    pNew->iOffset = -1;
  }
  return pNew;
}

/*
** Given 1 to 3 identifiers preceeding the JOIN keyword, determine the
** type of join.  Return an integer constant that expresses that type
................................................................................
  if( v==0 ) return 0;
  assert( pEList!=0 );

  /* If there was a LIMIT clause on the SELECT statement, then do the check
  ** to see if this row should be output.
  */
  if( pOrderBy==0 ){
    if( p->iOffset>=0 ){
      int addr = sqliteVdbeCurrentAddr(v);
      sqliteVdbeAddOp(v, OP_MemIncr, p->iOffset, addr+2);
      sqliteVdbeAddOp(v, OP_Goto, 0, iContinue);
    }
    if( p->iLimit>=0 ){
      sqliteVdbeAddOp(v, OP_MemIncr, p->iLimit, iBreak);
    }
  }

  /* Pull the requested columns.
  */
  if( nColumn>0 ){
    for(i=0; i<nColumn; i++){
................................................................................
  int iParm        /* Optional parameter associated with eDest */
){
  int end = sqliteVdbeMakeLabel(v);
  int addr;
  if( eDest==SRT_Sorter ) return;
  sqliteVdbeAddOp(v, OP_Sort, 0, 0);
  addr = sqliteVdbeAddOp(v, OP_SortNext, 0, end);
  if( p->iOffset>=0 ){
    sqliteVdbeAddOp(v, OP_MemIncr, p->iOffset, addr+4);
    sqliteVdbeAddOp(v, OP_Pop, 1, 0);
    sqliteVdbeAddOp(v, OP_Goto, 0, addr);
  }
  if( p->iLimit>=0 ){
    sqliteVdbeAddOp(v, OP_MemIncr, p->iLimit, end);
  }
  switch( eDest ){
    case SRT_Callback: {
      sqliteVdbeAddOp(v, OP_SortCallback, nColumn, 0);
      break;
    }
    case SRT_Table:
................................................................................
    if( pE->dataType==SQLITE_SO_NUM ) continue;
    assert( pE->iColumn>=0 );
    if( pEList->nExpr>pE->iColumn ){
      pE->dataType = sqliteExprType(pEList->a[pE->iColumn].pExpr);
    }
  }
}

/*
** Compute the iLimit and iOffset fields of the SELECT based on the
** nLimit and nOffset fields.  nLimit and nOffset hold the integers
** that appear in the original SQL statement after the LIMIT and OFFSET
** keywords.  Or that hold -1 and 0 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 if iLimit and iOffset only if
** a limit or offset is defined by nLimit and nOffset.  iLimit and
** iOffset should have been preset to appropriate default values
** (usually but not always -1) prior to calling this routine.
** Only if nLimit>=0 or nOffset>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){
  /* 
  ** If the comparison is p->nLimit>0 then "LIMIT 0" shows
  ** all rows.  It is the same as no limit. If the comparision is
  ** p->nLimit>=0 then "LIMIT 0" show no rows at all.
  ** "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->nLimit>=0 ){
    int iMem = pParse->nMem++;
    Vdbe *v = sqliteGetVdbe(pParse);
    if( v==0 ) return;
    sqliteVdbeAddOp(v, OP_Integer, -p->nLimit, 0);
    sqliteVdbeAddOp(v, OP_MemStore, iMem, 1);
    p->iLimit = iMem;
  }
  if( p->nOffset>0 ){
    int iMem = pParse->nMem++;
    Vdbe *v = sqliteGetVdbe(pParse);
    if( v==0 ) return;
    sqliteVdbeAddOp(v, OP_Integer, -p->nOffset, 0);
    sqliteVdbeAddOp(v, OP_MemStore, iMem, 1);
    p->iOffset = iMem;
  }
}

/*
** 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
................................................................................
** individual selects always group from left to right.
*/
static int multiSelect(Parse *pParse, Select *p, int eDest, int iParm){
  int rc;             /* Success code from a subroutine */
  Select *pPrior;     /* Another SELECT immediately to our left */
  Vdbe *v;            /* Generate code to this VDBE */

  /* Make sure there is no ORDER BY or LIMIT clause on prior SELECTs.  Only
  ** the last SELECT in the series may have an ORDER BY or LIMIT.
  */
  if( p==0 || p->pPrior==0 ) return 1;
  pPrior = p->pPrior;
  if( pPrior->pOrderBy ){
    sqliteErrorMsg(pParse,"ORDER BY clause should come after %s not before",
      selectOpName(p->op));
    return 1;
  }
  if( pPrior->nLimit>=0 || pPrior->nOffset>0 ){
    sqliteErrorMsg(pParse,"LIMIT clause should come after %s not before",
      selectOpName(p->op));
    return 1;
  }

  /* Make sure we have a valid query engine.  If not, create a new one.
  */
  v = sqliteGetVdbe(pParse);
  if( v==0 ) return 1;

................................................................................
  }

  /* Generate code for the left and right SELECT statements.
  */
  switch( p->op ){
    case TK_ALL: {
      if( p->pOrderBy==0 ){
        pPrior->nLimit = p->nLimit;
        pPrior->nOffset = p->nOffset;
        rc = sqliteSelect(pParse, pPrior, eDest, iParm, 0, 0, 0);
        if( rc ) return rc;
        p->pPrior = 0;
        p->iLimit = pPrior->iLimit;
        p->iOffset = pPrior->iOffset;
        p->nLimit = -1;
        p->nOffset = 0;
        rc = sqliteSelect(pParse, p, eDest, iParm, 0, 0, 0);
        p->pPrior = pPrior;
        if( rc ) return rc;
        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;          /* One of the SRT_ operations to apply to self */
      int priorOp;     /* The SRT_ operation to apply to prior selects */
      int nLimit, nOffset; /* Saved values of p->nLimit and p->nOffset */
      ExprList *pOrderBy;  /* The ORDER BY clause for the right SELECT */

      priorOp = p->op==TK_ALL ? SRT_Table : SRT_Union;
      if( eDest==priorOp && p->pOrderBy==0 && p->nLimit<0 && p->nOffset==0 ){
        /* 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.
................................................................................
         case TK_EXCEPT:  op = SRT_Except;   break;
         case TK_UNION:   op = SRT_Union;    break;
         case TK_ALL:     op = SRT_Table;    break;
      }
      p->pPrior = 0;
      pOrderBy = p->pOrderBy;
      p->pOrderBy = 0;
      nLimit = p->nLimit;
      p->nLimit = -1;
      nOffset = p->nOffset;
      p->nOffset = 0;
      rc = sqliteSelect(pParse, p, op, unionTab, 0, 0, 0);
      p->pPrior = pPrior;
      p->pOrderBy = pOrderBy;
      p->nLimit = nLimit;
      p->nOffset = nOffset;
      if( rc ) return rc;

      /* 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;
................................................................................
        if( eDest==SRT_Callback ){
          generateColumnNames(pParse, 0, p->pEList);
          generateColumnTypes(pParse, p->pSrc, p->pEList);
        }
        iBreak = sqliteVdbeMakeLabel(v);
        iCont = sqliteVdbeMakeLabel(v);
        sqliteVdbeAddOp(v, OP_Rewind, unionTab, iBreak);
        computeLimitRegisters(pParse, p);
        iStart = sqliteVdbeCurrentAddr(v);
        multiSelectSortOrder(p, p->pOrderBy);
        rc = selectInnerLoop(pParse, p, p->pEList, unionTab, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak);
        if( rc ) return 1;
        sqliteVdbeResolveLabel(v, iCont);
................................................................................
        }
      }
      break;
    }
    case TK_INTERSECT: {
      int tab1, tab2;
      int iCont, iBreak, iStart;
      int nLimit, nOffset;

      /* 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( rc ) return rc;

      /* Code the current SELECT into temporary table "tab2"
      */
      sqliteVdbeAddOp(v, OP_OpenTemp, tab2, 1);
      sqliteVdbeAddOp(v, OP_KeyAsData, tab2, 1);
      p->pPrior = 0;
      nLimit = p->nLimit;
      p->nLimit = -1;
      nOffset = p->nOffset;
      p->nOffset = 0;
      rc = sqliteSelect(pParse, p, SRT_Union, tab2, 0, 0, 0);
      p->pPrior = pPrior;
      p->nLimit = nLimit;
      p->nOffset = nOffset;
      if( rc ) return rc;

      /* Generate code to take the intersection of the two temporary
      ** tables.
      */
      assert( p->pEList );
      if( eDest==SRT_Callback ){
        generateColumnNames(pParse, 0, p->pEList);
        generateColumnTypes(pParse, p->pSrc, p->pEList);
      }
      iBreak = sqliteVdbeMakeLabel(v);
      iCont = sqliteVdbeMakeLabel(v);
      sqliteVdbeAddOp(v, OP_Rewind, tab1, iBreak);
      computeLimitRegisters(pParse, p);
      iStart = sqliteVdbeAddOp(v, OP_FullKey, tab1, 0);
      sqliteVdbeAddOp(v, OP_NotFound, tab2, iCont);
      multiSelectSortOrder(p, p->pOrderBy);
      rc = selectInnerLoop(pParse, p, p->pEList, tab1, p->pEList->nExpr,
                             p->pOrderBy, -1, eDest, iParm, 
                             iCont, iBreak);
      if( rc ) return 1;
................................................................................
  /* Generating code to find the min or the max.  Basically all we have
  ** to do is find the first or the last entry in the chosen index.  If
  ** the min() or max() is on the INTEGER PRIMARY KEY, then find the first
  ** or last entry in the main table.
  */
  sqliteCodeVerifySchema(pParse, pTab->iDb);
  base = p->pSrc->a[0].iCursor;
  computeLimitRegisters(pParse, p);
  sqliteVdbeAddOp(v, OP_Integer, pTab->iDb, 0);
  sqliteVdbeAddOp(v, OP_OpenRead, base, pTab->tnum);
  sqliteVdbeChangeP3(v, -1, pTab->zName, P3_STATIC);
  cont = sqliteVdbeMakeLabel(v);
  if( pIdx==0 ){
    sqliteVdbeAddOp(v, seekOp, base, 0);
  }else{
................................................................................
  /* Identify column names if we will be using them in a callback.  This
  ** step is skipped if the output is going to some other destination.
  */
  if( eDest==SRT_Callback ){
    generateColumnNames(pParse, pTabList, pEList);
  }


































  /* Check for the special case of a min() or max() function by itself
  ** in the result set.
  */
  if( simpleMinMaxQuery(pParse, p, eDest, iParm) ){
    rc = 0;
    goto select_end;
  }
................................................................................
  */
  if( pParent && pParentAgg &&
      flattenSubquery(pParse, pParent, parentTab, *pParentAgg, isAgg) ){
    if( isAgg ) *pParentAgg = 1;
    return rc;
  }

  /* Set the limiter.
  */
  computeLimitRegisters(pParse, p);

  /* Identify column types if we will be using a callback.  This
  ** step is skipped if the output is going to a destination other
  ** than a callback.
  **
  ** We have to do this separately from the creation of column names
  ** above because if the pTabList contains views then they will not
  ** have been resolved and we will not know the column types until

Changes to src/sqliteInt.h.

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**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.193 2003/06/23 11:06:02 drh Exp $
*/
#include "config.h"
#include "sqlite.h"
#include "hash.h"
#include "vdbe.h"
#include "parse.h"
#include "btree.h"
................................................................................
** nLimit is set to -1 if there is no LIMIT clause.  nOffset is set to 0.
** If there is a LIMIT clause, the parser sets nLimit to the value of the
** limit and nOffset to the value of the offset (or 0 if there is not
** offset).  But later on, nLimit and nOffset become the memory locations
** in the VDBE that record the limit and offset counters.
*/
struct Select {
  int isDistinct;        /* True if the DISTINCT keyword is present */
  ExprList *pEList;      /* The fields of the result */


  SrcList *pSrc;         /* The FROM clause */
  Expr *pWhere;          /* The WHERE clause */
  ExprList *pGroupBy;    /* The GROUP BY clause */
  Expr *pHaving;         /* The HAVING clause */
  ExprList *pOrderBy;    /* The ORDER BY clause */
  int op;                /* One of: TK_UNION TK_ALL TK_INTERSECT TK_EXCEPT */
  Select *pPrior;        /* Prior select in a compound select statement */
  int nLimit, nOffset;   /* LIMIT and OFFSET values.  -1 means not used */

  char *zSelect;         /* Complete text of the SELECT command */
};

/*
** The results of a select can be distributed in several ways.
*/
#define SRT_Callback     1  /* Invoke a callback with each row of result */







|







 







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**    May you do good and not evil.
**    May you find forgiveness for yourself and forgive others.
**    May you share freely, never taking more than you give.
**
*************************************************************************
** Internal interface definitions for SQLite.
**
** @(#) $Id: sqliteInt.h,v 1.194 2003/07/20 01:16:47 drh Exp $
*/
#include "config.h"
#include "sqlite.h"
#include "hash.h"
#include "vdbe.h"
#include "parse.h"
#include "btree.h"
................................................................................
** nLimit is set to -1 if there is no LIMIT clause.  nOffset is set to 0.
** If there is a LIMIT clause, the parser sets nLimit to the value of the
** limit and nOffset to the value of the offset (or 0 if there is not
** offset).  But later on, nLimit and nOffset become the memory locations
** in the VDBE that record the limit and offset counters.
*/
struct Select {

  ExprList *pEList;      /* The fields of the result */
  u8 op;                 /* One of: TK_UNION TK_ALL TK_INTERSECT TK_EXCEPT */
  u8 isDistinct;         /* True if the DISTINCT keyword is present */
  SrcList *pSrc;         /* The FROM clause */
  Expr *pWhere;          /* The WHERE clause */
  ExprList *pGroupBy;    /* The GROUP BY clause */
  Expr *pHaving;         /* The HAVING clause */
  ExprList *pOrderBy;    /* The ORDER BY clause */

  Select *pPrior;        /* Prior select in a compound select statement */
  int nLimit, nOffset;   /* LIMIT and OFFSET values.  -1 means not used */
  int iLimit, iOffset;   /* Memory registers holding LIMIT & OFFSET counters */
  char *zSelect;         /* Complete text of the SELECT command */
};

/*
** The results of a select can be distributed in several ways.
*/
#define SRT_Callback     1  /* Invoke a callback with each row of result */

Changes to test/limit.test.

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216
#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the LIMIT ... OFFSET ... clause
#  of SELECT statements.
#
# $Id: limit.test,v 1.9 2003/07/16 11:51:36 drh Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Build some test data
#
set fd [open data1.txt w]
................................................................................
  }
} {}
do_test limit-6.8 {
  execsql {
    SELECT * FROM t6 LIMIT 0 OFFSET 1
  }
} {}

















































































finish_test







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#    May you share freely, never taking more than you give.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the LIMIT ... OFFSET ... clause
#  of SELECT statements.
#
# $Id: limit.test,v 1.10 2003/07/20 01:16:48 drh Exp $

set testdir [file dirname $argv0]
source $testdir/tester.tcl

# Build some test data
#
set fd [open data1.txt w]
................................................................................
  }
} {}
do_test limit-6.8 {
  execsql {
    SELECT * FROM t6 LIMIT 0 OFFSET 1
  }
} {}

# Make sure LIMIT works well with compound SELECT statements.
# Ticket #393
#
do_test limit-7.1.1 {
  catchsql {
    SELECT x FROM t2 LIMIT 5 UNION ALL SELECT a FROM t6;
  }
} {1 {LIMIT clause should come after UNION ALL not before}}
do_test limit-7.1.2 {
  catchsql {
    SELECT x FROM t2 LIMIT 5 UNION SELECT a FROM t6;
  }
} {1 {LIMIT clause should come after UNION not before}}
do_test limit-7.1.3 {
  catchsql {
    SELECT x FROM t2 LIMIT 5 EXCEPT SELECT a FROM t6 LIMIT 3;
  }
} {1 {LIMIT clause should come after EXCEPT not before}}
do_test limit-7.1.4 {
  catchsql {
    SELECT x FROM t2 LIMIT 0,5 INTERSECT SELECT a FROM t6;
  }
} {1 {LIMIT clause should come after INTERSECT not before}}
do_test limit-7.2 {
  execsql {
    SELECT x FROM t2 UNION ALL SELECT a FROM t6 LIMIT 5;
  }
} {31 30 1 2 3}
do_test limit-7.3 {
  execsql {
    SELECT x FROM t2 UNION ALL SELECT a FROM t6 LIMIT 3 OFFSET 1;
  }
} {30 1 2}
do_test limit-7.4 {
  execsql {
    SELECT x FROM t2 UNION ALL SELECT a FROM t6 ORDER BY 1 LIMIT 3 OFFSET 1;
  }
} {2 3 4}
do_test limit-7.5 {
  execsql {
    SELECT x FROM t2 UNION SELECT x+2 FROM t2 LIMIT 2 OFFSET 1;
  }
} {31 32}
do_test limit-7.6 {
  execsql {
    SELECT x FROM t2 UNION SELECT x+2 FROM t2 ORDER BY 1 DESC LIMIT 2 OFFSET 1;
  }
} {32 31}
do_test limit-7.7 {
  execsql {
    SELECT a+9 FROM t6 EXCEPT SELECT y FROM t2 LIMIT 2;
  }
} {11 12}
do_test limit-7.8 {
  execsql {
    SELECT a+9 FROM t6 EXCEPT SELECT y FROM t2 ORDER BY 1 DESC LIMIT 2;
  }
} {13 12}
do_test limit-7.9 {
  execsql {
    SELECT a+26 FROM t6 INTERSECT SELECT x FROM t2 LIMIT 1;
  }
} {30}
do_test limit-7.10 {
  execsql {
    SELECT a+27 FROM t6 INTERSECT SELECT x FROM t2 LIMIT 1;
  }
} {30}
do_test limit-7.11 {
  execsql {
    SELECT a+27 FROM t6 INTERSECT SELECT x FROM t2 LIMIT 1 OFFSET 1;
  }
} {31}
do_test limit-7.12 {
  execsql {
    SELECT a+27 FROM t6 INTERSECT SELECT x FROM t2 
       ORDER BY 1 DESC LIMIT 1 OFFSET 1;
  }
} {30}

finish_test

Changes to www/lang.tcl.

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#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: lang.tcl,v 1.64 2003/07/16 11:51:36 drh Exp $}

puts {<html>
<head>
  <title>Query Language Understood By SQLite</title>
</head>
<body bgcolor=white>
<h1 align=center>
................................................................................
expression must exactly match one of the result columns.  Each
sort expression may be optionally followed by ASC or DESC to specify
the sort order.</p>

<p>The LIMIT clause places an upper bound on the number of rows
returned in the result.  A negative LIMIT indicates no upper bound.
The optional OFFSET following LIMIT specifies how many
rows to skip at the beginning of the result set.</p>






<p>A compound SELECT is formed from two or more simple SELECTs connected
by one of the operators UNION, UNION ALL, INTERSECT, or EXCEPT.  In
a compound SELECT, all the constituent SELECTs must specify the
same number of result columns.  There may be only a single ORDER BY
clause at the end of the compound SELECT.  The UNION and UNION ALL
operators combine the results of the SELECTs to the right and left into



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#
# Run this Tcl script to generate the sqlite.html file.
#
set rcsid {$Id: lang.tcl,v 1.65 2003/07/20 01:16:48 drh Exp $}

puts {<html>
<head>
  <title>Query Language Understood By SQLite</title>
</head>
<body bgcolor=white>
<h1 align=center>
................................................................................
expression must exactly match one of the result columns.  Each
sort expression may be optionally followed by ASC or DESC to specify
the sort order.</p>

<p>The LIMIT clause places an upper bound on the number of rows
returned in the result.  A negative LIMIT indicates no upper bound.
The optional OFFSET following LIMIT specifies how many
rows to skip at the beginning of the result set.
In a compound query, the LIMIT clause may only appear on the
final SELECT statement.
The limit is applied to the entire query not
to the individual SELECT statement to which it is attached.
</p>

<p>A compound SELECT is formed from two or more simple SELECTs connected
by one of the operators UNION, UNION ALL, INTERSECT, or EXCEPT.  In
a compound SELECT, all the constituent SELECTs must specify the
same number of result columns.  There may be only a single ORDER BY
clause at the end of the compound SELECT.  The UNION and UNION ALL
operators combine the results of the SELECTs to the right and left into