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Overview
Comment:Scan an index instead of a table for "SELECT count(*) FROM <tbl>" queries. Because an index is usually smaller than a table on disk, this saves some IO. (CVS 6315)
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Timelines: family | ancestors | descendants | both | trunk
Files: files | file ages | folders
SHA1: 294ba6f743c9132dce0e73da480bd3c2071e7239
User & Date: danielk1977 2009-02-23 17:33:50.000
Context
2009-02-24
10:01
Optimize queries of the form "SELECT count(*) FROM <tbl>" by adding a sqlite3BtreeCount() interface to the btree layer. (CVS 6316) (check-in: d4aa659318 user: danielk1977 tags: trunk)
2009-02-23
17:33
Scan an index instead of a table for "SELECT count(*) FROM <tbl>" queries. Because an index is usually smaller than a table on disk, this saves some IO. (CVS 6315) (check-in: 294ba6f743 user: danielk1977 tags: trunk)
16:52
Add the reverse_unordered_selects pragma. (CVS 6314) (check-in: bc078e0007 user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/delete.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
** in order to generate code for DELETE FROM statements.
**
** $Id: delete.c,v 1.193 2009/02/20 10:58:42 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** Look up every table that is named in pSrc.  If any table is not found,
** add an error message to pParse->zErrMsg and return NULL.  If all tables
** are found, return a pointer to the last table.







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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
** in order to generate code for DELETE FROM statements.
**
** $Id: delete.c,v 1.194 2009/02/23 17:33:50 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** Look up every table that is named in pSrc.  If any table is not found,
** add an error message to pParse->zErrMsg and return NULL.  If all tables
** are found, return a pointer to the last table.
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  {
    int iRowid = ++pParse->nMem;    /* Used for storing rowid values. */
    int iRowSet = ++pParse->nMem;   /* Register for rowset of rows to delete */

    /* Collect rowids of every row to be deleted.
    */
    sqlite3VdbeAddOp2(v, OP_Null, 0, iRowSet);

    pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0,
                               WHERE_FILL_ROWSET, iRowSet);
    if( pWInfo==0 ) goto delete_from_cleanup;
    if( db->flags & SQLITE_CountRows ){
      sqlite3VdbeAddOp2(v, OP_AddImm, memCnt, 1);
    }
    sqlite3WhereEnd(pWInfo);







>







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  {
    int iRowid = ++pParse->nMem;    /* Used for storing rowid values. */
    int iRowSet = ++pParse->nMem;   /* Register for rowset of rows to delete */

    /* Collect rowids of every row to be deleted.
    */
    sqlite3VdbeAddOp2(v, OP_Null, 0, iRowSet);
    pTabList->a[0].usesRowid = 1;
    pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0,
                               WHERE_FILL_ROWSET, iRowSet);
    if( pWInfo==0 ) goto delete_from_cleanup;
    if( db->flags & SQLITE_CountRows ){
      sqlite3VdbeAddOp2(v, OP_AddImm, memCnt, 1);
    }
    sqlite3WhereEnd(pWInfo);
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 1.414 2009/02/20 10:58:42 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** Return the 'affinity' of the expression pExpr if any.
**
** If pExpr is a column, a reference to a column via an 'AS' alias,







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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 1.415 2009/02/23 17:33:50 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** Return the 'affinity' of the expression pExpr if any.
**
** If pExpr is a column, a reference to a column via an 'AS' alias,
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    if( pTab ){
      pTab->nRef++;
    }
    pNewItem->pSelect = sqlite3SelectDup(db, pOldItem->pSelect, flags);
    pNewItem->pOn = sqlite3ExprDup(db, pOldItem->pOn, flags);
    pNewItem->pUsing = sqlite3IdListDup(db, pOldItem->pUsing);
    pNewItem->colUsed = pOldItem->colUsed;

  }
  return pNew;
}
IdList *sqlite3IdListDup(sqlite3 *db, IdList *p){
  IdList *pNew;
  int i;
  if( p==0 ) return 0;







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    if( pTab ){
      pTab->nRef++;
    }
    pNewItem->pSelect = sqlite3SelectDup(db, pOldItem->pSelect, flags);
    pNewItem->pOn = sqlite3ExprDup(db, pOldItem->pOn, flags);
    pNewItem->pUsing = sqlite3IdListDup(db, pOldItem->pUsing);
    pNewItem->colUsed = pOldItem->colUsed;
    pNewItem->usesRowid = pOldItem->usesRowid;
  }
  return pNew;
}
IdList *sqlite3IdListDup(sqlite3 *db, IdList *p){
  IdList *pNew;
  int i;
  if( p==0 ) return 0;
Changes to src/resolve.c.
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**
*************************************************************************
**
** This file contains routines used for walking the parser tree and
** resolve all identifiers by associating them with a particular
** table and column.
**
** $Id: resolve.c,v 1.16 2009/02/19 14:39:25 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include <stdlib.h>
#include <string.h>

/*
** Turn the pExpr expression into an alias for the iCol-th column of the







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**
*************************************************************************
**
** This file contains routines used for walking the parser tree and
** resolve all identifiers by associating them with a particular
** table and column.
**
** $Id: resolve.c,v 1.17 2009/02/23 17:33:50 danielk1977 Exp $
*/
#include "sqliteInt.h"
#include <stdlib.h>
#include <string.h>

/*
** Turn the pExpr expression into an alias for the iCol-th column of the
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  /* If a column from a table in pSrcList is referenced, then record
  ** this fact in the pSrcList.a[].colUsed bitmask.  Column 0 causes
  ** bit 0 to be set.  Column 1 sets bit 1.  And so forth.  If the
  ** column number is greater than the number of bits in the bitmask
  ** then set the high-order bit of the bitmask.
  */

  if( pExpr->iColumn>=0 && pMatch!=0 ){
    int n = pExpr->iColumn;
    testcase( n==BMS-1 );
    if( n>=BMS ){
      n = BMS-1;
    }
    assert( pMatch->iCursor==pExpr->iTable );
    pMatch->colUsed |= ((Bitmask)1)<<n;



  }

lookupname_end:
  /* Clean up and return
  */
  sqlite3DbFree(db, zDb);
  sqlite3DbFree(db, zTab);







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  /* If a column from a table in pSrcList is referenced, then record
  ** this fact in the pSrcList.a[].colUsed bitmask.  Column 0 causes
  ** bit 0 to be set.  Column 1 sets bit 1.  And so forth.  If the
  ** column number is greater than the number of bits in the bitmask
  ** then set the high-order bit of the bitmask.
  */
  if( pMatch ){
    if( pExpr->iColumn>=0 ){
      int n = pExpr->iColumn;
      testcase( n==BMS-1 );
      if( n>=BMS ){
        n = BMS-1;
      }
      assert( pMatch->iCursor==pExpr->iTable );
      pMatch->colUsed |= ((Bitmask)1)<<n;
    }else{
      pMatch->usesRowid = 1;
    }
  }

lookupname_end:
  /* Clean up and return
  */
  sqlite3DbFree(db, zDb);
  sqlite3DbFree(db, zTab);
Changes to src/sqliteInt.h.
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/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    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 1.835 2009/02/23 16:52:08 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build













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/*
** 2001 September 15
**
** The author disclaims copyright to this source code.  In place of
** a legal notice, here is a blessing:
**
**    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 1.836 2009/02/23 17:33:50 danielk1977 Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Include the configuration header output by 'configure' if we're using the
** autoconf-based build
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    char *zName;      /* Name of the table */
    char *zAlias;     /* The "B" part of a "A AS B" phrase.  zName is the "A" */
    Table *pTab;      /* An SQL table corresponding to zName */
    Select *pSelect;  /* A SELECT statement used in place of a table name */
    u8 isPopulated;   /* Temporary table associated with SELECT is populated */
    u8 jointype;      /* Type of join between this able and the previous */
    u8 notIndexed;    /* True if there is a NOT INDEXED clause */

    int iCursor;      /* The VDBE cursor number used to access this table */
    Expr *pOn;        /* The ON clause of a join */
    IdList *pUsing;   /* The USING clause of a join */
    Bitmask colUsed;  /* Bit N (1<<N) set if column N of pTab is used */
    char *zIndex;     /* Identifier from "INDEXED BY <zIndex>" clause */
    Index *pIndex;    /* Index structure corresponding to zIndex, if any */
  } a[1];             /* One entry for each identifier on the list */







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    char *zName;      /* Name of the table */
    char *zAlias;     /* The "B" part of a "A AS B" phrase.  zName is the "A" */
    Table *pTab;      /* An SQL table corresponding to zName */
    Select *pSelect;  /* A SELECT statement used in place of a table name */
    u8 isPopulated;   /* Temporary table associated with SELECT is populated */
    u8 jointype;      /* Type of join between this able and the previous */
    u8 notIndexed;    /* True if there is a NOT INDEXED clause */
    u8 usesRowid;     /* True if the rowid field is read */
    int iCursor;      /* The VDBE cursor number used to access this table */
    Expr *pOn;        /* The ON clause of a join */
    IdList *pUsing;   /* The USING clause of a join */
    Bitmask colUsed;  /* Bit N (1<<N) set if column N of pTab is used */
    char *zIndex;     /* Identifier from "INDEXED BY <zIndex>" clause */
    Index *pIndex;    /* Index structure corresponding to zIndex, if any */
  } a[1];             /* One entry for each identifier on the list */
Changes to src/update.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 UPDATE statements.
**
** $Id: update.c,v 1.193 2009/02/20 10:58:42 danielk1977 Exp $
*/
#include "sqliteInt.h"

#ifndef SQLITE_OMIT_VIRTUALTABLE
/* Forward declaration */
static void updateVirtualTable(
  Parse *pParse,       /* The parsing context */







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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 UPDATE statements.
**
** $Id: update.c,v 1.194 2009/02/23 17:33:50 danielk1977 Exp $
*/
#include "sqliteInt.h"

#ifndef SQLITE_OMIT_VIRTUALTABLE
/* Forward declaration */
static void updateVirtualTable(
  Parse *pParse,       /* The parsing context */
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  if( sqlite3ResolveExprNames(&sNC, pWhere) ){
    goto update_cleanup;
  }

  /* Begin the database scan
  */
  sqlite3VdbeAddOp2(v, OP_Null, 0, regOldRowid);

  pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0,
                             WHERE_ONEPASS_DESIRED, 0);
  if( pWInfo==0 ) goto update_cleanup;
  okOnePass = pWInfo->okOnePass;

  /* Remember the rowid of every item to be updated.
  */







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  if( sqlite3ResolveExprNames(&sNC, pWhere) ){
    goto update_cleanup;
  }

  /* Begin the database scan
  */
  sqlite3VdbeAddOp2(v, OP_Null, 0, regOldRowid);
  pTabList->a[0].usesRowid = 1;
  pWInfo = sqlite3WhereBegin(pParse, pTabList, pWhere, 0,
                             WHERE_ONEPASS_DESIRED, 0);
  if( pWInfo==0 ) goto update_cleanup;
  okOnePass = pWInfo->okOnePass;

  /* Remember the rowid of every item to be updated.
  */
Changes to src/where.c.
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** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is responsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.371 2009/02/23 16:52:08 drh Exp $
*/
#include "sqliteInt.h"

/*
** Trace output macros
*/
#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)







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** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is responsible for
** generating the code that loops through a table looking for applicable
** rows.  Indices are selected and used to speed the search when doing
** so is applicable.  Because this module is responsible for selecting
** indices, you might also think of this module as the "query optimizer".
**
** $Id: where.c,v 1.372 2009/02/23 17:33:50 danielk1977 Exp $
*/
#include "sqliteInt.h"

/*
** Trace output macros
*/
#if defined(SQLITE_TEST) || defined(SQLITE_DEBUG)
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**       fewer the better.)
**
**    *  Whether or not sorting must occur.
**
**    *  Whether or not there must be separate lookups in the
**       index and in the main table.
**
** If there was an INDEXED BY clause attached to the table in the SELECT
** statement, then this function only considers plans using the 
** named index. If one cannot be found, then the returned cost is
** SQLITE_BIG_DBL. If a plan can be found that uses the named index, 
** then the cost is calculated in the usual way.
**
** If a NOT INDEXED clause was attached to the table in the SELECT 
** statement, then no indexes are considered. However, the selected 
** plan may still take advantage of the tables built-in rowid
** index.
*/
static void bestIndex(
  Parse *pParse,              /* The parsing context */
  WhereClause *pWC,           /* The WHERE clause */
  struct SrcList_item *pSrc,  /* The FROM clause term to search */
  Bitmask notReady,           /* Mask of cursors that are not available */







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**       fewer the better.)
**
**    *  Whether or not sorting must occur.
**
**    *  Whether or not there must be separate lookups in the
**       index and in the main table.
**
** If there was an INDEXED BY clause (pSrc->pIndex) attached to the table in
** the SQL statement, then this function only considers plans using the 
** named index. If one cannot be found, then the returned cost is
** SQLITE_BIG_DBL. If a plan can be found that uses the named index, 
** then the cost is calculated in the usual way.
**
** If a NOT INDEXED clause (pSrc->notIndexed!=0) was attached to the table 
** in the SELECT statement, then no indexes are considered. However, the 
** selected plan may still take advantage of the tables built-in rowid
** index.
*/
static void bestIndex(
  Parse *pParse,              /* The parsing context */
  WhereClause *pWC,           /* The WHERE clause */
  struct SrcList_item *pSrc,  /* The FROM clause term to search */
  Bitmask notReady,           /* Mask of cursors that are not available */
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      pCost->nRow = nRow;
      pCost->plan.wsFlags = wsFlags;
      pCost->plan.nEq = nEq;
      assert( pCost->plan.wsFlags & WHERE_INDEXED );
      pCost->plan.u.pIdx = pProbe;
    }
  }
















  /* Report the best result
  */
  pCost->plan.wsFlags |= eqTermMask;
  WHERETRACE(("best index is %s, cost=%.9g, nrow=%.9g, wsFlags=%x, nEq=%d\n",
        (pCost->plan.wsFlags & WHERE_INDEXED)!=0 ?
             pCost->plan.u.pIdx->zName : "(none)", pCost->nRow,







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      pCost->nRow = nRow;
      pCost->plan.wsFlags = wsFlags;
      pCost->plan.nEq = nEq;
      assert( pCost->plan.wsFlags & WHERE_INDEXED );
      pCost->plan.u.pIdx = pProbe;
    }
  }

  if( pCost->plan.wsFlags==0 && pSrc->colUsed==0 && pSrc->usesRowid==0 ){
    Index *pSmallest = 0;
    assert( pSrc->pIndex==0 );
    for(pProbe=pSrc->pTab->pIndex; pProbe; pProbe=pProbe->pNext){
      if( !pSmallest || pProbe->nColumn<pSmallest->nColumn ){
        pSmallest = pProbe;
      }
    }
    if( pSmallest && pSmallest->nColumn<pSrc->pTab->nCol ){
      assert( pCost->plan.nEq==0 );
      pCost->plan.u.pIdx = pSmallest;
      pCost->plan.wsFlags = WHERE_COLUMN_RANGE|WHERE_IDX_ONLY;
    }
  }

  /* Report the best result
  */
  pCost->plan.wsFlags |= eqTermMask;
  WHERETRACE(("best index is %s, cost=%.9g, nrow=%.9g, wsFlags=%x, nEq=%d\n",
        (pCost->plan.wsFlags & WHERE_INDEXED)!=0 ?
             pCost->plan.u.pIdx->zName : "(none)", pCost->nRow,
Changes to test/where9.test.
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# 2008 December 30
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    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.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the multi-index OR clause optimizer.
#
# $Id: where9.test,v 1.5 2009/01/08 21:00:03 drh Exp $

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

ifcapable !or_opt {
  finish_test
  return













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# 2008 December 30
#
# The author disclaims copyright to this source code.  In place of
# a legal notice, here is a blessing:
#
#    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.
#
#***********************************************************************
# This file implements regression tests for SQLite library.  The
# focus of this file is testing the multi-index OR clause optimizer.
#
# $Id: where9.test,v 1.6 2009/02/23 17:33:50 danielk1977 Exp $

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

ifcapable !or_opt {
  finish_test
  return
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  catchsql {
    UPDATE t1 INDEXED BY t1b SET a=a+100
     WHERE (b IS NULL AND c NOT NULL AND d NOT NULL)
        OR (b NOT NULL AND c IS NULL AND d NOT NULL)
        OR (b NOT NULL AND c NOT NULL AND d IS NULL)
  }
} {1 {cannot use index: t1b}}



























finish_test








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>
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>
>
>
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>
>
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797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
  catchsql {
    UPDATE t1 INDEXED BY t1b SET a=a+100
     WHERE (b IS NULL AND c NOT NULL AND d NOT NULL)
        OR (b NOT NULL AND c IS NULL AND d NOT NULL)
        OR (b NOT NULL AND c NOT NULL AND d IS NULL)
  }
} {1 {cannot use index: t1b}}

do_test where9-7.1 {
  execsql {
    CREATE TABLE t5(a, b, c);
    EXPLAIN QUERY PLAN SELECT count(*) FROM t5;
  }
} {0 0 {TABLE t5}}
do_test where9-7.2 {
  execsql {
    CREATE INDEX t5i1 ON t5(a, b);
    EXPLAIN QUERY PLAN SELECT count(*) FROM t5;
  }
} {0 0 {TABLE t5 WITH INDEX t5i1}}
do_test where9-7.3 {
  execsql {
    CREATE INDEX t5i2 ON t5(b);
    EXPLAIN QUERY PLAN SELECT count(*) FROM t5;
  }
} {0 0 {TABLE t5 WITH INDEX t5i2}}
do_test where9-7.4 {
  execsql {
    CREATE TABLE t6(a, b, c);
    CREATE INDEX t6i1 ON t6(a, b, c);
    EXPLAIN QUERY PLAN SELECT count(*) FROM t6;
  }
} {0 0 {TABLE t6}}

finish_test