SQLite

** stored in pIdx->aSample[]. 
*/
static void initAvgEq(Index *pIdx){
  if( pIdx ){
    IndexSample *aSample = pIdx->aSample;
    IndexSample *pFinal = &aSample[pIdx->nSample-1];
    int iCol;
    int nCol = 1;
    if( pIdx->nSampleCol>1 ){
      /* If this is stat4 data, then calculate aAvgEq[] values for all
      ** sample columns except the last. The last is always set to 1, as
      ** once the trailing PK fields are considered all index keys are
      ** unique.  */
      nCol = pIdx->nSampleCol-1;
      pIdx->aAvgEq[nCol] = 1;
    }
    for(iCol=0; iCol<pIdx->nKeyCol; iCol++){
    for(iCol=0; iCol<nCol; iCol++){
      int i;                    /* Used to iterate through samples */
      tRowcnt sumEq = 0;        /* Sum of the nEq values */
      tRowcnt nSum = 0;         /* Number of terms contributing to sumEq */
      tRowcnt avgEq = 0;
      tRowcnt nDLt = pFinal->anDLt[iCol];

      /* Set nSum to the number of distinct (iCol+1) field prefixes that

        }
      }
      if( nDLt>nSum ){
        avgEq = (pFinal->anLt[iCol] - sumEq)/(nDLt - nSum);
      }
      if( avgEq==0 ) avgEq = 1;
      pIdx->aAvgEq[iCol] = avgEq;
      if( pIdx->nSampleCol==1 ) break;
    }
  }
}

/*
** Look up an index by name.  Or, if the name of a WITHOUT ROWID table
** is supplied instead, find the PRIMARY KEY index for that table.

  }
  rc = sqlite3_prepare(db, zSql, -1, &pStmt, 0);
  sqlite3DbFree(db, zSql);
  if( rc ) return rc;

  while( sqlite3_step(pStmt)==SQLITE_ROW ){
    int nIdxCol = 1;              /* Number of columns in stat4 records */
    int nAvgCol = 1;              /* Number of entries in Index.aAvgEq */

    char *zIndex;   /* Index name */
    Index *pIdx;    /* Pointer to the index object */
    int nSample;    /* Number of samples */
    int nByte;      /* Bytes of space required */
    int i;          /* Bytes of space required */
    tRowcnt *pSpace;

    zIndex = (char *)sqlite3_column_text(pStmt, 0);
    if( zIndex==0 ) continue;
    nSample = sqlite3_column_int(pStmt, 1);
    pIdx = findIndexOrPrimaryKey(db, zIndex, zDb);
    assert( pIdx==0 || bStat3 || pIdx->nSample==0 );
    /* Index.nSample is non-zero at this point if data has already been
    ** loaded from the stat4 table. In this case ignore stat3 data.  */
    if( pIdx==0 || pIdx->nSample ) continue;
    if( bStat3==0 ){
      assert( !HasRowid(pIdx->pTable) || pIdx->nColumn==pIdx->nKeyCol+1 );
      if( !HasRowid(pIdx->pTable) && IsPrimaryKeyIndex(pIdx) ){
      nIdxCol = pIdx->nKeyCol+1;
      nAvgCol = pIdx->nKeyCol;
        nIdxCol = pIdx->nKeyCol;
      }else{
        nIdxCol = pIdx->nColumn;
      }
    }
    pIdx->nSampleCol = nIdxCol;
    nByte = sizeof(IndexSample) * nSample;
    nByte += sizeof(tRowcnt) * nIdxCol * 3 * nSample;
    nByte += nAvgCol * sizeof(tRowcnt);     /* Space for Index.aAvgEq[] */
    nByte += nIdxCol * sizeof(tRowcnt);     /* Space for Index.aAvgEq[] */

    pIdx->aSample = sqlite3DbMallocZero(db, nByte);
    if( pIdx->aSample==0 ){
      sqlite3_finalize(pStmt);
      return SQLITE_NOMEM;
    }
    pSpace = (tRowcnt*)&pIdx->aSample[nSample];
    pIdx->aAvgEq = pSpace; pSpace += nAvgCol;
    pIdx->aAvgEq = pSpace; pSpace += nIdxCol;
    for(i=0; i<nSample; i++){
      pIdx->aSample[i].anEq = pSpace; pSpace += nIdxCol;
      pIdx->aSample[i].anLt = pSpace; pSpace += nIdxCol;
      pIdx->aSample[i].anDLt = pSpace; pSpace += nIdxCol;
    }
    assert( ((u8*)pSpace)-nByte==(u8*)(pIdx->aSample) );
  }

      iLower = 0;
      iUpper = aSample[0].anLt[iCol];
    }else{
      i64 nRow0 = sqlite3LogEstToInt(pIdx->aiRowLogEst[0]);
      iUpper = i>=pIdx->nSample ? nRow0 : aSample[i].anLt[iCol];
      iLower = aSample[i-1].anEq[iCol] + aSample[i-1].anLt[iCol];
    }
    aStat[1] = (pIdx->nKeyCol>iCol ? pIdx->aAvgEq[iCol] : 1);
    aStat[1] = pIdx->aAvgEq[iCol];
    if( iLower>=iUpper ){
      iGap = 0;
    }else{
      iGap = iUpper - iLower;
    }
    if( roundUp ){
      iGap = (iGap*2)/3;

# and (d<20) over (c='one' AND a='A').
foreach {tn where res} {
  1 "c='one' AND a='B' AND d < 20"   {/*INDEX i3 (c=? AND a=?)*/}
  2 "c='one' AND a='A' AND d < 20"   {/*INDEX i4 (d<?)*/}
} {
  do_eqp_test 22.2.$tn "SELECT * FROM t3 WHERE $where" $res
}

proc int_to_char {i} {
  set ret ""
  set char [list a b c d e f g h i j]
  foreach {div} {1000 100 10 1} {
    append ret [lindex $char [expr ($i / $div) % 10]]
  }
  set ret
}
db func int_to_char int_to_char

do_execsql_test 23.0 {
  CREATE TABLE t4(
    a COLLATE nocase, b, c, 
    d, e, f, 
    PRIMARY KEY(c, b, a)
  ) WITHOUT ROWID;
  CREATE INDEX i41 ON t4(e);
  CREATE INDEX i42 ON t4(f);

  WITH data(a, b, c, d, e, f) AS (
    SELECT int_to_char(0), 'xyz', 'zyx', '*', 0, 0
    UNION ALL
    SELECT 
      int_to_char(f+1), b, c, d, (e+1) % 2, f+1
    FROM data WHERE f<1024
  )
  INSERT INTO t4 SELECT a, b, c, d, e, f FROM data;
  ANALYZE;
} {}

do_eqp_test 23.1 {
  SELECT * FROM t4 WHERE 
    (e=1 AND b='xyz' AND c='zyx' AND a<'AEA') AND f<300
} {
  0 0 0 {SEARCH TABLE t4 USING INDEX i41 (e=? AND c=? AND b=? AND a<?)}
}

do_eqp_test 23.2 {
  SELECT * FROM t4 WHERE 
    (e=1 AND b='xyz' AND c='zyx' AND a<'JJJ') AND f<300
} {
  0 0 0 {SEARCH TABLE t4 USING INDEX i42 (f<?)}
}

finish_test