SQLite

/*
** 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 1.533 2007/01/19 01:06:02 drh Exp $
*/
#ifndef _SQLITEINT_H_
#define _SQLITEINT_H_

/*
** Extra interface definitions for those who need them
*/

** the SrcList.a[] array.
**
** With the addition of multiple database support, the following structure
** can also be used to describe a particular table such as the table that
** is modified by an INSERT, DELETE, or UPDATE statement.  In standard SQL,
** such a table must be a simple name: ID.  But in SQLite, the table can
** now be identified by a database name, a dot, then the table name: ID.ID.
**
** The jointype starts out showing the join type between the current table
** and the next table on the list.  The parser builds the list this way.
** But sqlite3SrcListShiftJoinType() later shifts the jointypes so that each
** jointype expresses the join between the table and the previous table.
*/
struct SrcList {
  i16 nSrc;        /* Number of tables or subqueries in the FROM clause */
  i16 nAlloc;      /* Number of entries allocated in a[] below */
  struct SrcList_item {
    char *zDatabase;  /* Name of database holding this table */
    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 */
    i16 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 or pTab is used */
  } a[1];             /* One entry for each identifier on the list */
};

** This module contains C code that generates VDBE code used to process
** the WHERE clause of SQL statements.  This module is reponsible 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 1.235 2007/01/19 01:06:03 drh Exp $
*/
#include "sqliteInt.h"

/*
** The number of bits in a Bitmask.  "BMS" means "BitMask Size".
*/
#define BMS  (sizeof(Bitmask)*8)

  int bestFlags = 0;          /* Flags associated with bestIdx */
  int bestNEq = 0;            /* Best value for nEq */
  int iCur = pSrc->iCursor;   /* The cursor of the table to be accessed */
  Index *pProbe;              /* An index we are evaluating */
  int rev;                    /* True to scan in reverse order */
  int flags;                  /* Flags associated with pProbe */
  int nEq;                    /* Number of == or IN constraints */
  int eqTermMask;             /* Mask of valid equality operators */
  double cost;                /* Cost of using pProbe */

  TRACE(("bestIndex: tbl=%s notReady=%x\n", pSrc->pTab->zName, notReady));
  lowestCost = SQLITE_BIG_DBL;
  pProbe = pSrc->pTab->pIndex;

  /* If the table has no indices and there are no terms in the where

      TRACE(("... sorting increases cost to %.9g\n", cost));
    }
  }
  if( cost<lowestCost ){
    lowestCost = cost;
    bestFlags = flags;
  }

  /* If the pSrc table is the right table of a LEFT JOIN then we may not
  ** use an index to satisfy IS NULL constraints on that table.  This is
  ** because columns might end up being NULL if the table does not match -
  ** a circumstance which the index cannot help us discover.  Ticket #2177.
  */
  if( (pSrc->jointype & JT_LEFT)!=0 ){
    eqTermMask = WO_EQ|WO_IN;
  }else{
    eqTermMask = WO_EQ|WO_IN|WO_ISNULL;
  }

  /* Look at each index.
  */
  for(; pProbe; pProbe=pProbe->pNext){
    int i;                       /* Loop counter */
    double inMultiplier = 1;

    TRACE(("... index %s:\n", pProbe->zName));

    /* Count the number of columns in the index that are satisfied
    ** by x=EXPR constraints or x IN (...) constraints.
    */
    flags = 0;
    for(i=0; i<pProbe->nColumn; i++){
      int j = pProbe->aiColumn[i];
      pTerm = findTerm(pWC, iCur, j, notReady, eqTermMask, pProbe);
      if( pTerm==0 ) break;
      flags |= WHERE_COLUMN_EQ;
      if( pTerm->eOperator & WO_IN ){
        Expr *pExpr = pTerm->pExpr;
        flags |= WHERE_COLUMN_IN;
        if( pExpr->pSelect!=0 ){
          inMultiplier *= 25;

  if( pLevel->flags & WHERE_COLUMN_IN ){
    pParse->nMem += pLevel->nEq;
    termsInMem = 1;
  }

  /* Evaluate the equality constraints
  */
  assert( pIdx->nColumn>=nEq );
  for(j=0; j<nEq; j++){
    int k = pIdx->aiColumn[j];
    pTerm = findTerm(pWC, iCur, k, notReady, WO_EQ|WO_IN|WO_ISNULL, pIdx);
    if( pTerm==0 ) break;
    assert( (pTerm->flags & TERM_CODED)==0 );
    codeEqualityTerm(pParse, pTerm, brk, pLevel);
    if( (pTerm->eOperator & WO_ISNULL)==0 ){
      sqlite3VdbeAddOp(v, OP_IsNull, termsInMem ? -1 : -(j+1), brk);
    }
    if( termsInMem ){
      sqlite3VdbeAddOp(v, OP_MemStore, pLevel->iMem+j+1, 1);
    }
  }


  /* Make sure all the constraint values are on the top of the stack
  */
  if( termsInMem ){
    for(j=0; j<nEq; j++){
      sqlite3VdbeAddOp(v, OP_MemLoad, pLevel->iMem+j+1, 0);
    }

# 2006 October 27
#
# 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 use of indices in WHERE clauses.
# This file was created when support for optimizing IS NULL phrases
# was added.  And so the principle purpose of this file is to test
# that IS NULL phrases are correctly optimized.  But you can never
# have too many tests, so some other tests are thrown in as well.
#
# $Id: where4.test,v 1.1 2007/01/19 01:06:03 drh Exp $

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

# Build some test data
#
do_test where4-1.0 {
  execsql {
    CREATE TABLE t1(w, x, y);
    CREATE INDEX i1wxy ON t1(w,x,y);
    INSERT INTO t1 VALUES(1,2,3);
    INSERT INTO t1 VALUES(1,NULL,3);
    INSERT INTO t1 VALUES('a','b','c');
    INSERT INTO t1 VALUES('a',NULL,'c');
    INSERT INTO t1 VALUES(X'78',x'79',x'7a');
    INSERT INTO t1 VALUES(X'78',NULL,X'7A');
    INSERT INTO t1 VALUES(NULL,NULL,NULL);
    SELECT count(*) FROM t1;
  }
} {7}

# Do an SQL statement.  Append the search count to the end of the result.
#
proc count sql {
  set ::sqlite_search_count 0
  return [concat [execsql $sql] $::sqlite_search_count]
}

# Verify that queries use an index.  We are using the special variable
# "sqlite_search_count" which tallys the number of executions of MoveTo
# and Next operators in the VDBE.  By verifing that the search count is
# small we can be assured that indices are being used properly.
#
do_test where4-1.1 {
  count {SELECT rowid FROM t1 WHERE w IS NULL}
} {7 2}
do_test where4-1.2 {
  count {SELECT rowid FROM t1 WHERE +w IS NULL}
} {7 6}
do_test where4-1.3 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x IS NULL}
} {2 2}
do_test where4-1.4 {
  count {SELECT rowid FROM t1 WHERE w=1 AND +x IS NULL}
} {2 3}
do_test where4-1.5 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x>0}
} {1 2}
do_test where4-1.6 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x<9}
} {1 3}
do_test where4-1.7 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x IS NULL AND y=3}
} {2 2}
do_test where4-1.8 {
  count {SELECT rowid FROM t1 WHERE w=1 AND x IS NULL AND y>2}
} {2 2}
do_test where4-1.9 {
  count {SELECT rowid FROM t1 WHERE w='a' AND x IS NULL AND y='c'}
} {4 2}
do_test where4-1.10 {
  count {SELECT rowid FROM t1 WHERE w=x'78' AND x IS NULL}
} {6 2}
do_test where4-1.11 {
  count {SELECT rowid FROM t1 WHERE w=x'78' AND x IS NULL AND y=123}
} {1}
do_test where4-1.12 {
  count {SELECT rowid FROM t1 WHERE w=x'78' AND x IS NULL AND y=x'7A'}
} {6 2}
do_test where4-1.13 {
  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL}
} {7 2}
do_test where4-1.14 {
  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL AND y IS NULL}
} {7 2}
do_test where4-1.15 {
  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL AND y<0}
} {2}
do_test where4-1.16 {
  count {SELECT rowid FROM t1 WHERE w IS NULL AND x IS NULL AND y>=0}
} {1}

do_test where4-2.1 {
  execsql {SELECT rowid FROM t1 ORDER BY w, x, y}
} {7 2 1 4 3 6 5}
do_test where4-2.2 {
  execsql {SELECT rowid FROM t1 ORDER BY w DESC, x, y}
} {6 5 4 3 2 1 7}
do_test where4-2.3 {
  execsql {SELECT rowid FROM t1 ORDER BY w, x DESC, y}
} {7 1 2 3 4 5 6}


# Ticket #2177
#
# Suppose you have a left join where the right table of the left
# join (the one that can be NULL) has an index on two columns.
# The first indexed column is used in the ON clause of the join.
# The second indexed column is used in the WHERE clause with an IS NULL
# constraint.  It is not allowed to use the IS NULL optimization to
# optimize the query because the second column might be NULL because
# the right table did not match - something the index does not know
# about.
#
do_test where4-3.1 {
  execsql {
    CREATE TABLE t2(a);
    INSERT INTO t2 VALUES(1);
    INSERT INTO t2 VALUES(2);
    INSERT INTO t2 VALUES(3);
    CREATE TABLE t3(x,y,UNIQUE(x,y));
    INSERT INTO t3 VALUES(1,11);
    INSERT INTO t3 VALUES(2,NULL);
 
    SELECT * FROM t2 LEFT JOIN t3 ON a=x WHERE +y IS NULL;
  }
} {2 2 {} 3 {} {}}
do_test where4-3.2 {
  execsql {
    SELECT * FROM t2 LEFT JOIN t3 ON a=x WHERE y IS NULL;
  }
} {2 2 {} 3 {} {}}

integrity_check {where4-99.0}

finish_test