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Overview
Comment:Adjustments to the result row estimator for the IN operator so that it gives the same estimates as the equivalent OR operator. Test cases for the same.
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SHA1: c82cb9c028b3ba5463ae50c30196dbf157a7a305
User & Date: drh 2011-01-21 18:18:13
Context
2011-01-22
00:10
Add the ability to use indices for constraints of the form "x IS NOT NULL" when sqlite_stat2 is available and most entries for column x are NULL. check-in: 5d5bddd2 user: drh tags: stat2-enhancement
2011-01-21
18:18
Adjustments to the result row estimator for the IN operator so that it gives the same estimates as the equivalent OR operator. Test cases for the same. check-in: c82cb9c0 user: drh tags: stat2-enhancement
16:27
Make use of histogram data to make better estimates for the number of rows that will be returned from "x IN (v1,v2,v3,...)" constraints. check-in: fd3977a2 user: drh tags: stat2-enhancement
Changes
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Changes to src/where.c.

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#define TERM_DYNAMIC    0x01   /* Need to call sqlite3ExprDelete(db, pExpr) */
#define TERM_VIRTUAL    0x02   /* Added by the optimizer.  Do not code */
#define TERM_CODED      0x04   /* This term is already coded */
#define TERM_COPIED     0x08   /* Has a child */
#define TERM_ORINFO     0x10   /* Need to free the WhereTerm.u.pOrInfo object */
#define TERM_ANDINFO    0x20   /* Need to free the WhereTerm.u.pAndInfo obj */
#define TERM_OR_OK      0x40   /* Used during OR-clause processing */


/*
** An instance of the following structure holds all information about a
** WHERE clause.  Mostly this is a container for one or more WhereTerms.
*/
struct WhereClause {
  Parse *pParse;           /* The parser context */
................................................................................
        exprAnalyze(pSrc, pWC, idxNew);
        pTerm = &pWC->a[idxTerm];
        pWC->a[idxNew].iParent = idxTerm;
        pTerm->nChild = 1;
      }else{
        sqlite3ExprListDelete(db, pList);
      }

      pTerm->eOperator = 0;  /* case 1 trumps case 2 */
    }
  }
}
#endif /* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */


................................................................................
  return rc;
}
#endif /* defined(SQLITE_ENABLE_STAT2) */

#ifdef SQLITE_ENABLE_STAT2
/*
** Estimate the number of rows that will be returned based on
** an IN constraint "x IN (V1,V2,V3,...)" where the right-hand side
** of the IN operator is a list of values.


**
** Write the estimated row count into *pnRow and return SQLITE_OK. 
** If unable to make an estimate, leave *pnRow unchanged and return
** non-zero.
**
** This routine can fail if it is unable to load a collating sequence
** required for string comparison, or if unable to allocate memory
................................................................................
  Index *p,            /* The index whose left-most column is pTerm */
  ExprList *pList,     /* The value list on the RHS of "x IN (v1,v2,v3,...)" */
  double *pnRow        /* Write the revised row estimate here */
){
  sqlite3_value *pVal = 0;  /* One value from list */
  int iLower, iUpper;       /* Range of histogram regions containing pRhs */
  u8 aff;                   /* Column affinity */
  int rc;                   /* Subfunction return code */
  double nRowEst;           /* New estimate of the number of rows */
  int nRegion = 0;          /* Number of histogram regions spanned */
  int nSingle = 0;          /* Count of values contained within one region */
  int nNotFound = 0;        /* Count of values that are not constants */
  int i;                            /* Loop counter */

  u8 aHit[SQLITE_INDEX_SAMPLES+1];  /* Histogram regions that are spanned */

  assert( p->aSample!=0 );
  aff = p->pTable->aCol[p->aiColumn[0]].affinity;
  memset(aHit, 0, sizeof(aHit));

  for(i=0; i<pList->nExpr; i++){
    sqlite3ValueFree(pVal);
    rc = valueFromExpr(pParse, pList->a[i].pExpr, aff, &pVal);
    if( rc ) break;
    if( pVal==0 ){
      nNotFound++;
      continue;
    }
    rc = whereRangeRegion(pParse, p, pVal, 0, &iLower);
    if( rc ) break;
    rc = whereRangeRegion(pParse, p, pVal, 1, &iUpper);
    if( rc ) break;
    if( iLower>=iUpper ){
      nSingle++;
    }
    assert( iLower>=0 && iUpper<=SQLITE_INDEX_SAMPLES );
    while( iLower<=iUpper ) aHit[iLower++] = 1;
  }

  if( rc==SQLITE_OK ){
    for(i=nRegion=0; i<ArraySize(aHit); i++) nRegion += aHit[i];
    nRowEst = nRegion*p->aiRowEst[0]/(SQLITE_INDEX_SAMPLES+1)







               + nNotFound*p->aiRowEst[1];
    if( nRowEst > p->aiRowEst[0] ) nRowEst = p->aiRowEst[0];
    *pnRow = nRowEst;
    WHERETRACE(("IN row estimate: nRegion=%d, nSingle=%d, nNotFound=%d\n",
                 nRegion, nSingle, nNotFound));
  }
  sqlite3ValueFree(pVal);
  return rc;
}
#endif /* defined(SQLITE_ENABLE_STAT2) */


................................................................................
      int k;                       /* Loop counter */
      int nSkipEq = nEq;           /* Number of == constraints to skip */
      int nSkipRange = nBound;     /* Number of < constraints to skip */
      Bitmask thisTab;             /* Bitmap for pSrc */

      thisTab = getMask(pWC->pMaskSet, iCur);
      for(pTerm=pWC->a, k=pWC->nTerm; nRow>2 && k; k--, pTerm++){
        if( pTerm->wtFlags & TERM_VIRTUAL ) continue;
        if( (pTerm->prereqAll & notValid)!=thisTab ) continue;
        if( pTerm->eOperator & (WO_EQ|WO_IN|WO_ISNULL) ){
          if( nSkipEq ){
            /* Ignore the first nEq equality matches since the index
            ** has already accounted for these */
            nSkipEq--;
          }else{
            /* Assume each additional equality match reduces the result
            ** set size by a factor of 10 */
            nRow /= 10;
          }
        }else if( pTerm->eOperator & (WO_LT|WO_LE|WO_GT|WO_GE) ){
          if( nSkipRange ){
            /* Ignore the first nBound range constraints since the index
            ** has already accounted for these */
            nSkipRange--;
          }else{
            /* Assume each additional range constraint reduces the result
            ** set size by a factor of 3 */
            nRow /= 3;
          }







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#define TERM_DYNAMIC    0x01   /* Need to call sqlite3ExprDelete(db, pExpr) */
#define TERM_VIRTUAL    0x02   /* Added by the optimizer.  Do not code */
#define TERM_CODED      0x04   /* This term is already coded */
#define TERM_COPIED     0x08   /* Has a child */
#define TERM_ORINFO     0x10   /* Need to free the WhereTerm.u.pOrInfo object */
#define TERM_ANDINFO    0x20   /* Need to free the WhereTerm.u.pAndInfo obj */
#define TERM_OR_OK      0x40   /* Used during OR-clause processing */
#define TERM_NOHELP     0x80   /* This term does not reduce the search space */

/*
** An instance of the following structure holds all information about a
** WHERE clause.  Mostly this is a container for one or more WhereTerms.
*/
struct WhereClause {
  Parse *pParse;           /* The parser context */
................................................................................
        exprAnalyze(pSrc, pWC, idxNew);
        pTerm = &pWC->a[idxTerm];
        pWC->a[idxNew].iParent = idxTerm;
        pTerm->nChild = 1;
      }else{
        sqlite3ExprListDelete(db, pList);
      }
      pTerm->wtFlags |= TERM_NOHELP;
      pTerm->eOperator = 0;  /* case 1 trumps case 2 */
    }
  }
}
#endif /* !SQLITE_OMIT_OR_OPTIMIZATION && !SQLITE_OMIT_SUBQUERY */


................................................................................
  return rc;
}
#endif /* defined(SQLITE_ENABLE_STAT2) */

#ifdef SQLITE_ENABLE_STAT2
/*
** Estimate the number of rows that will be returned based on
** an IN constraint where the right-hand side of the IN operator
** is a list of values.  Example:
**
**        WHERE x IN (1,2,3,4)
**
** Write the estimated row count into *pnRow and return SQLITE_OK. 
** If unable to make an estimate, leave *pnRow unchanged and return
** non-zero.
**
** This routine can fail if it is unable to load a collating sequence
** required for string comparison, or if unable to allocate memory
................................................................................
  Index *p,            /* The index whose left-most column is pTerm */
  ExprList *pList,     /* The value list on the RHS of "x IN (v1,v2,v3,...)" */
  double *pnRow        /* Write the revised row estimate here */
){
  sqlite3_value *pVal = 0;  /* One value from list */
  int iLower, iUpper;       /* Range of histogram regions containing pRhs */
  u8 aff;                   /* Column affinity */
  int rc = SQLITE_OK;       /* Subfunction return code */
  double nRowEst;           /* New estimate of the number of rows */
  int nSpan = 0;            /* Number of histogram regions spanned */
  int nSingle = 0;          /* Histogram regions hit by a single value */
  int nNotFound = 0;        /* Count of values that are not constants */
  int i;                               /* Loop counter */
  u8 aSpan[SQLITE_INDEX_SAMPLES+1];    /* Histogram regions that are spanned */
  u8 aSingle[SQLITE_INDEX_SAMPLES+1];  /* Histogram regions hit once */

  assert( p->aSample!=0 );
  aff = p->pTable->aCol[p->aiColumn[0]].affinity;
  memset(aSpan, 0, sizeof(aSpan));
  memset(aSingle, 0, sizeof(aSingle));
  for(i=0; i<pList->nExpr; i++){
    sqlite3ValueFree(pVal);
    rc = valueFromExpr(pParse, pList->a[i].pExpr, aff, &pVal);
    if( rc ) break;
    if( pVal==0 || sqlite3_value_type(pVal)==SQLITE_NULL ){
      nNotFound++;
      continue;
    }
    rc = whereRangeRegion(pParse, p, pVal, 0, &iLower);
    if( rc ) break;
    rc = whereRangeRegion(pParse, p, pVal, 1, &iUpper);
    if( rc ) break;
    if( iLower>=iUpper ){
      aSingle[iLower] = 1;
    }else{
      assert( iLower>=0 && iUpper<=SQLITE_INDEX_SAMPLES );
      while( iLower<iUpper ) aSpan[iLower++] = 1;
    }
  }
  if( rc==SQLITE_OK ){

    for(i=nSpan=0; i<=SQLITE_INDEX_SAMPLES; i++){
      if( aSpan[i] ){
        nSpan++;
      }else if( aSingle[i] ){
        nSingle++;
      }
    }
    nRowEst = (nSpan*2+nSingle)*p->aiRowEst[0]/(2*SQLITE_INDEX_SAMPLES)
               + nNotFound*p->aiRowEst[1];
    if( nRowEst > p->aiRowEst[0] ) nRowEst = p->aiRowEst[0];
    *pnRow = nRowEst;
    WHERETRACE(("IN row estimate: nSpan=%d, nSingle=%d, nNotFound=%d, est=%g\n",
                 nSpan, nSingle, nNotFound, nRowEst));
  }
  sqlite3ValueFree(pVal);
  return rc;
}
#endif /* defined(SQLITE_ENABLE_STAT2) */


................................................................................
      int k;                       /* Loop counter */
      int nSkipEq = nEq;           /* Number of == constraints to skip */
      int nSkipRange = nBound;     /* Number of < constraints to skip */
      Bitmask thisTab;             /* Bitmap for pSrc */

      thisTab = getMask(pWC->pMaskSet, iCur);
      for(pTerm=pWC->a, k=pWC->nTerm; nRow>2 && k; k--, pTerm++){
        if( pTerm->wtFlags & (TERM_VIRTUAL|TERM_NOHELP) ) continue;
        if( (pTerm->prereqAll & notValid)!=thisTab ) continue;
        if( pTerm->eOperator & (WO_EQ|WO_IN|WO_ISNULL) ){
          if( nSkipEq ){
            /* Ignore the first nEq equality matches since the index
            ** has already accounted for these */
            nSkipEq--;
          }else{
            /* Assume each additional equality match reduces the result
            ** set size by a factor of 10 */
            nRow /= 10;
          }
        }else if( pTerm->eOperator & (WO_LT|WO_LE|WO_GT|WO_GE) ){
          if( nSkipRange ){
            /* Ignore the first nSkipRange range constraints since the index
            ** has already accounted for these */
            nSkipRange--;
          }else{
            /* Assume each additional range constraint reduces the result
            ** set size by a factor of 3 */
            nRow /= 3;
          }

Changes to test/analyze5.test.

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  114  {z=2.5}           50
} {
  do_test analyze5-1.$testid {
    eqp "SELECT * FROM t1 WHERE $where"
  } [format {0 0 0 {SEARCH TABLE t1 USING INDEX t1z (z=?) (~%d rows)}} $rows]
}

































# For the t1.y column, most entries are known to be zero.  So do a 
# full table scan for y=0 but use the index for any other constraint on
# y.
#
do_test analyze5-201 {
  eqp {SELECT * FROM t1 WHERE y=0}







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  113  {z=1.5}           50
  114  {z=2.5}           50
} {
  do_test analyze5-1.$testid {
    eqp "SELECT * FROM t1 WHERE $where"
  } [format {0 0 0 {SEARCH TABLE t1 USING INDEX t1z (z=?) (~%d rows)}} $rows]
}

# for the next sequence of tests a value of rows<=0 means a full-table scan
# is used.
#
#set sqlite_where_trace 1
foreach {testid where rows} {
  201  {z IN (-1)}            50
  202  {z IN (0)}            400
  203  {z IN (1)}            300
  204  {z IN (2)}            200
  205  {z IN (3)}            100
  206  {z IN (4)}             50
  207  {z IN (0.5)}           50
  208  {z IN (0,1)}          700
  209  {z IN (0,1,2)}        900
  210  {z IN (0,1,2,3)}        0
  211  {z IN (0,1,2,3,4,5)}    0
  212  {z IN (1,2)}          500
  213  {z IN (2,3)}          300
  214  {z=3 OR z=2}          300
  215  {z IN (-1,3)}         150
  216  {z=-1 OR z=3}         150
} {
  if {$rows<=0} {
    set ans {SCAN TABLE t1 (~100 rows)}
  } else {
    set ans [format {SEARCH TABLE t1 USING INDEX t1z (z=?) (~%d rows)} $rows]
  }
  do_test analyze5-1.$testid {
    lindex [eqp "SELECT * FROM t1 WHERE $where"] 3
  } $ans
}

# For the t1.y column, most entries are known to be zero.  So do a 
# full table scan for y=0 but use the index for any other constraint on
# y.
#
do_test analyze5-201 {
  eqp {SELECT * FROM t1 WHERE y=0}