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Overview
Comment:Skip-ahead does not always work. So we still have to check for redundancy.
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SHA1: db5a2364ebfbb6e54e0141ca57ccabdcc83ac41d
User & Date: drh 2016-04-15 16:17:31.207
Context
2016-04-15
16:27
Skip-ahead is now just an optimization. If it gets confused, it falls back to an incremental scan with redundancy elimination. (check-in: 6fac0b9212 user: drh tags: skip-ahead-distinct)
16:17
Skip-ahead does not always work. So we still have to check for redundancy. (check-in: db5a2364eb user: drh tags: skip-ahead-distinct)
15:54
Fixes to the skip-ahead distinct logic. More issues remain. (check-in: 45a70b2bb8 user: drh tags: skip-ahead-distinct)
Changes
Unified Diff Ignore Whitespace Patch
Changes to src/select.c.
︙︙
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  /* If the DISTINCT keyword was present on the SELECT statement
  ** and this row has been seen before, then do not make this row
  ** part of the result.
  */
  if( hasDistinct ){
    switch( pDistinct->eTnctType ){
      case WHERE_DISTINCT_ORDERED: {
#if 0
        VdbeOp *pOp;            /* No longer required OpenEphemeral instr. */
        int iJump;              /* Jump destination */
        int regPrev;            /* Previous row content */

        /* Allocate space for the previous row */
        regPrev = pParse->nMem+1;
        pParse->nMem += nResultCol;








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  /* If the DISTINCT keyword was present on the SELECT statement
  ** and this row has been seen before, then do not make this row
  ** part of the result.
  */
  if( hasDistinct ){
    switch( pDistinct->eTnctType ){
      case WHERE_DISTINCT_ORDERED: {
#if 1
        VdbeOp *pOp;            /* No longer required OpenEphemeral instr. */
        int iJump;              /* Jump destination */
        int regPrev;            /* Previous row content */

        /* Allocate space for the previous row */
        regPrev = pParse->nMem+1;
        pParse->nMem += nResultCol;
︙︙
Changes to test/distinct2.test.
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  CREATE TABLE t5(a INT, b INT);
  CREATE UNIQUE INDEX t5x ON t5(a+b);
  INSERT INTO t5(a,b) VALUES(0,0),(1,0),(1,1),(0,3);
  CREATE TEMP TABLE out AS SELECT DISTINCT a+b FROM t5;
  SELECT * FROM out ORDER BY 1;
} {0 1 2 3}









finish_test








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  CREATE TABLE t5(a INT, b INT);
  CREATE UNIQUE INDEX t5x ON t5(a+b);
  INSERT INTO t5(a,b) VALUES(0,0),(1,0),(1,1),(0,3);
  CREATE TEMP TABLE out AS SELECT DISTINCT a+b FROM t5;
  SELECT * FROM out ORDER BY 1;
} {0 1 2 3}

do_execsql_test 600 {
  CREATE TABLE t6a(x INTEGER PRIMARY KEY);
  INSERT INTO t6a VALUES(1);
  CREATE TABLE t6b(y INTEGER PRIMARY KEY);
  INSERT INTO t6b VALUES(2),(3);
  SELECT DISTINCT x, x FROM t6a, t6b;
} {1 1}

finish_test