SQLite

**    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 1.198 2004/07/19 23:16:39 drh Exp $
*/
#include "sqliteInt.h"


/*
** Allocate a new Select structure and return a pointer to that
** structure.

  int i;
  for(i=0; i<pOrderBy->nExpr; i++){
    sqlite3ExprCode(pParse, pOrderBy->a[i].pExpr);
  }
  sqlite3VdbeAddOp(v, OP_MakeRecord, pOrderBy->nExpr, 0);
  sqlite3VdbeAddOp(v, OP_SortPut, 0, 0);
}

/*
** Add code to implement the OFFSET and LIMIT
*/
static void codeLimiter(
  Parse *pParse,    /* Parsing context */
  Select *p,        /* The SELECT statement being coded */
  int iContinue,    /* Jump here to skip the current record */
  int iBreak,       /* Jump here to end the loop */
  int nPop          /* Number of times to pop stack when jumping */
){
  Vdbe *v = pParse->pVdbe;
  if( p->iOffset>=0 ){
    int addr = sqlite3VdbeCurrentAddr(v) + 2;
    if( nPop>0 ) addr++;
    sqlite3VdbeAddOp(v, OP_MemIncr, p->iOffset, addr);
    if( nPop>0 ){
      sqlite3VdbeAddOp(v, OP_Pop, nPop, 0);
    }
    sqlite3VdbeAddOp(v, OP_Goto, 0, iContinue);
  }
  if( p->iLimit>=0 ){
    sqlite3VdbeAddOp(v, OP_MemIncr, p->iLimit, iBreak);
  }
}

/*
** This routine generates the code for the inside of the inner loop
** of a SELECT.
**
** If srcTab and nColumn are both zero, then the pEList expressions
** are evaluated in order to get the data for this row.  If nColumn>0

  int iParm,              /* An argument to the disposal method */
  int iContinue,          /* Jump here to continue with next row */
  int iBreak,             /* Jump here to break out of the inner loop */
  char *aff               /* affinity string if eDest is SRT_Union */
){
  Vdbe *v = pParse->pVdbe;
  int i;
  int hasDistinct;        /* True if the DISTINCT keyword is present */

  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.
  */
  hasDistinct = distinct>=0 && pEList && pEList->nExpr>0;
  if( pOrderBy==0 && !hasDistinct ){



    codeLimiter(pParse, p, iContinue, iBreak, 0);




  }

  /* Pull the requested columns.
  */
  if( nColumn>0 ){
    for(i=0; i<nColumn; i++){
      sqlite3VdbeAddOp(v, OP_Column, srcTab, i);
    }
  }else{
    nColumn = pEList->nExpr;
    for(i=0; i<pEList->nExpr; i++){
      sqlite3ExprCode(pParse, pEList->a[i].pExpr);
    }
  }

  /* If the DISTINCT keyword was present on the SELECT statement
  ** and this row has been seen before, then do not make this row
  ** part of the result.
  */
  if( hasDistinct ){
#if NULL_ALWAYS_DISTINCT
    sqlite3VdbeAddOp(v, OP_IsNull, -pEList->nExpr, sqlite3VdbeCurrentAddr(v)+7);
#endif
    /* Deliberately leave the affinity string off of the following
    ** OP_MakeRecord */
    sqlite3VdbeAddOp(v, OP_MakeRecord, pEList->nExpr * -1, 0);
    sqlite3VdbeAddOp(v, OP_Distinct, distinct, sqlite3VdbeCurrentAddr(v)+3);
    sqlite3VdbeAddOp(v, OP_Pop, pEList->nExpr+1, 0);
    sqlite3VdbeAddOp(v, OP_Goto, 0, iContinue);
    sqlite3VdbeAddOp(v, OP_String8, 0, 0);
    sqlite3VdbeAddOp(v, OP_PutStrKey, distinct, 0);
    if( pOrderBy==0 ){
      codeLimiter(pParse, p, iContinue, iBreak, nColumn);
    }
  }

  switch( eDest ){
    /* In this mode, write each query result to the key of the temporary
    ** table iParm.
    */
    case SRT_Union: {

    if( !pInfo->aColl[i] ){
      pInfo->aColl[i] = db->pDfltColl;
    }
    pInfo->aSortOrder[i] = pOrderBy->a[i].sortOrder;
  }
  sqlite3VdbeOp3(v, OP_Sort, 0, 0, (char*)pInfo, P3_KEYINFO_HANDOFF);
  addr = sqlite3VdbeAddOp(v, OP_SortNext, 0, end1);





  codeLimiter(pParse, p, addr, end2, 1);


  switch( eDest ){
    case SRT_Table:
    case SRT_TempTable: {
      sqlite3VdbeAddOp(v, OP_NewRecno, iParm, 0);
      sqlite3VdbeAddOp(v, OP_Pull, 1, 0);
      sqlite3VdbeAddOp(v, OP_PutIntKey, iParm, 0);
      break;

#    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 1.14 2004/07/19 23:16:39 drh Exp $

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

# Build some test data
#
execsql {

} {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}

# Tests for limit in conjunction with distinct
#
do_test limit-8.1 {
  execsql {
    SELECT DISTINCT x/100 FROM t3 LIMIT 5;
  }
} {0 1 2 3 4}
do_test limit-8.2 {
  execsql {
    SELECT DISTINCT x/100 FROM t3 LIMIT 5 OFFSET 5;
  }
} {5 6 7 8 9}

finish_test