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Overview
Comment:Improved fix for ticket [ced41c7c7d6b4d36] that keeps skip-scan enabled, but avoids identifying a skip-scan as order-distinct (because it is not) and thus forces a separate b-tree to implement the DISTINCT clause of a query. This undoes check-in [a871d69c6de65038] and substitutes a new fix.
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SHA3-256: 89bf0399e87be76e7b264e0a35e8a6d3af0f9e71123a929c20754882b636ca70
User & Date: drh 2019-07-30 14:22:10.200
Context
2019-07-30
21:00
Fix the build for when -DSQLITE_SMALL_STACK is used. (check-in: b9eda2249a user: drh tags: trunk)
14:22
Improved fix for ticket [ced41c7c7d6b4d36] that keeps skip-scan enabled, but avoids identifying a skip-scan as order-distinct (because it is not) and thus forces a separate b-tree to implement the DISTINCT clause of a query. This undoes check-in [a871d69c6de65038] and substitutes a new fix. (check-in: 89bf0399e8 user: drh tags: trunk)
01:17
Disable the skip-scan optimization for DISTINCT queries. Fix for ticket [ced41c7c7d6b4d36] (check-in: a871d69c6d user: drh tags: trunk)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/where.c.
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  ** more expensive.  */
  assert( 42==sqlite3LogEst(18) );
  if( saved_nEq==saved_nSkip
   && saved_nEq+1<pProbe->nKeyCol
   && pProbe->noSkipScan==0
   && OptimizationEnabled(db, SQLITE_SkipScan)
   && pProbe->aiRowLogEst[saved_nEq+1]>=42  /* TUNING: Minimum for skip-scan */
   && (pWInfo->wctrlFlags & (WHERE_WANT_DISTINCT|WHERE_DISTINCTBY))==0
   && (rc = whereLoopResize(db, pNew, pNew->nLTerm+1))==SQLITE_OK
  ){
    LogEst nIter;
    pNew->u.btree.nEq++;
    pNew->nSkip++;
    pNew->aLTerm[pNew->nLTerm++] = 0;
    pNew->wsFlags |= WHERE_SKIPSCAN;








<








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  ** more expensive.  */
  assert( 42==sqlite3LogEst(18) );
  if( saved_nEq==saved_nSkip
   && saved_nEq+1<pProbe->nKeyCol
   && pProbe->noSkipScan==0
   && OptimizationEnabled(db, SQLITE_SkipScan)
   && pProbe->aiRowLogEst[saved_nEq+1]>=42  /* TUNING: Minimum for skip-scan */

   && (rc = whereLoopResize(db, pNew, pNew->nLTerm+1))==SQLITE_OK
  ){
    LogEst nIter;
    pNew->u.btree.nEq++;
    pNew->nSkip++;
    pNew->aLTerm[pNew->nLTerm++] = 0;
    pNew->wsFlags |= WHERE_SKIPSCAN;
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        return 0;
      }else{
        nKeyCol = pIndex->nKeyCol;
        nColumn = pIndex->nColumn;
        assert( nColumn==nKeyCol+1 || !HasRowid(pIndex->pTable) );
        assert( pIndex->aiColumn[nColumn-1]==XN_ROWID
                          || !HasRowid(pIndex->pTable));
        isOrderDistinct = IsUniqueIndex(pIndex);

      }

      /* Loop through all columns of the index and deal with the ones
      ** that are not constrained by == or IN.
      */
      rev = revSet = 0;
      distinctColumns = 0;








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        return 0;
      }else{
        nKeyCol = pIndex->nKeyCol;
        nColumn = pIndex->nColumn;
        assert( nColumn==nKeyCol+1 || !HasRowid(pIndex->pTable) );
        assert( pIndex->aiColumn[nColumn-1]==XN_ROWID
                          || !HasRowid(pIndex->pTable));
        isOrderDistinct = IsUniqueIndex(pIndex)
                          && (pLoop->wsFlags & WHERE_SKIPSCAN)==0;
      }

      /* Loop through all columns of the index and deal with the ones
      ** that are not constrained by == or IN.
      */
      rev = revSet = 0;
      distinctColumns = 0;
︙︙
Changes to test/skipscan1.test.
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  SELECT a,b,c,d,'|' FROM t6 WHERE d<>99 AND b=345 ORDER BY a DESC;
} {/* USING INDEX t6abc (ANY(a) AND b=?)*/}
do_execsql_test skipscan1-2.3 {
  SELECT a,b,c,d,'|' FROM t6 WHERE d<>99 AND b=345 ORDER BY a DESC;
} {}

# 2019-07-29 Ticket ced41c7c7d6b4d36
# Skip-scan is disabled for DISTINCT queries
#
db close
sqlite3 db :memory:
do_execsql_test skipscan1-3.1 {
  CREATE TABLE t1 (c1, c2, c3, c4, PRIMARY KEY(c4, c3));
  INSERT INTO t1 VALUES(NULL,0,1,NULL);
  INSERT INTO t1 VALUES(0,NULL,1,NULL);
  INSERT INTO t1 VALUES(NULL,NULL,1,NULL);

  ANALYZE sqlite_master;
  INSERT INTO sqlite_stat1 VALUES('t1','sqlite_autoindex_t1_1','18 18 6');
  ANALYZE sqlite_master;
  SELECT DISTINCT quote(c1), quote(c2), quote(c3), quote(c4), '|'
    FROM t1 WHERE t1.c3 = 1;
} {NULL 0 1 NULL | 0 NULL 1 NULL | NULL NULL 1 NULL |}









finish_test








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  SELECT a,b,c,d,'|' FROM t6 WHERE d<>99 AND b=345 ORDER BY a DESC;
} {/* USING INDEX t6abc (ANY(a) AND b=?)*/}
do_execsql_test skipscan1-2.3 {
  SELECT a,b,c,d,'|' FROM t6 WHERE d<>99 AND b=345 ORDER BY a DESC;
} {}

# 2019-07-29 Ticket ced41c7c7d6b4d36
# A skipscan query is not order-distinct
#
db close
sqlite3 db :memory:
do_execsql_test skipscan1-3.1 {
  CREATE TABLE t1 (c1, c2, c3, c4, PRIMARY KEY(c4, c3));
  INSERT INTO t1 VALUES(3,0,1,NULL);
  INSERT INTO t1 VALUES(0,4,1,NULL);
  INSERT INTO t1 VALUES(5,6,1,NULL);
  INSERT INTO t1 VALUES(0,4,1,NULL);
  ANALYZE sqlite_master;
  INSERT INTO sqlite_stat1 VALUES('t1','sqlite_autoindex_t1_1','18 18 6');
  ANALYZE sqlite_master;
  SELECT DISTINCT quote(c1), quote(c2), quote(c3), quote(c4), '|'
    FROM t1 WHERE t1.c3 = 1;
} {3 0 1 NULL | 0 4 1 NULL | 5 6 1 NULL |}
do_eqp_test skipscan1-3.2 {
  SELECT DISTINCT quote(c1), quote(c2), quote(c3), quote(c4), '|'
    FROM t1 WHERE t1.c3 = 1;
} {
  QUERY PLAN
  |--SEARCH TABLE t1 USING INDEX sqlite_autoindex_t1_1 (ANY(c4) AND c3=?)
  `--USE TEMP B-TREE FOR DISTINCT
}

finish_test