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Overview
| Comment: | Make sure that a DISTINCT query with an ORDER BY works correctly even if it uses a descending index. Fix for ticket [c5ea805691bfc4204b1cb9e]. |
|---|---|
| Downloads: | Tarball | ZIP archive | SQL archive |
| Timelines: | family | ancestors | descendants | both | trunk |
| Files: | files | file ages | folders |
| SHA1: |
0d3aef97ebddf422b8bdcbc5878970c6 |
| User & Date: | drh 2014-12-04 21:54:58 |
Context
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2014-12-05
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| 00:17 | Fix the autoconf and MSVC makefiles, which have been broken for nearly a month. :-( (check-in: 520c2b83 user: drh tags: trunk) | |
|
2014-12-04
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| 23:42 | Import from trunk support for SQLITE_CHECKPOINT_TRUNCATE and fixes for a couple of obscure bugs. (check-in: 463ad971 user: drh tags: apple-osx) | |
| 23:35 | Incorporate the SQLITE_CHECKPOINT_TRUNCATE enhancement and a couple of obscure bug fixes from trunk. (check-in: 34ffa3b3 user: drh tags: sessions) | |
| 21:54 | Make sure that a DISTINCT query with an ORDER BY works correctly even if it uses a descending index. Fix for ticket [c5ea805691bfc4204b1cb9e]. (check-in: 0d3aef97 user: drh tags: trunk) | |
| 20:24 | Performance enhancement for single-table queries with many OR-connected WHERE clause terms and multiple indexes with the same left-most columns. (check-in: 1461d543 user: drh tags: trunk) | |
Changes
Changes to src/select.c.
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** if the select-list is the same as the ORDER BY list, then this query
** can be rewritten as a GROUP BY. In other words, this:
**
** SELECT DISTINCT xyz FROM ... ORDER BY xyz
**
** is transformed to:
**
** SELECT xyz FROM ... GROUP BY xyz
**
** The second form is preferred as a single index (or temp-table) may be
** used for both the ORDER BY and DISTINCT processing. As originally
** written the query must use a temp-table for at least one of the ORDER
** BY and DISTINCT, and an index or separate temp-table for the other.
*/
if( (p->selFlags & (SF_Distinct|SF_Aggregate))==SF_Distinct
&& sqlite3ExprListCompare(sSort.pOrderBy, p->pEList, -1)==0
){
p->selFlags &= ~SF_Distinct;
p->pGroupBy = sqlite3ExprListDup(db, p->pEList, 0);
pGroupBy = p->pGroupBy;
sSort.pOrderBy = 0;
/* Notice that even thought SF_Distinct has been cleared from p->selFlags,
** the sDistinct.isTnct is still set. Hence, isTnct represents the
** original setting of the SF_Distinct flag, not the current setting */
assert( sDistinct.isTnct );
}
/* If there is an ORDER BY clause, then this sorting
|
| < |
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** if the select-list is the same as the ORDER BY list, then this query
** can be rewritten as a GROUP BY. In other words, this:
**
** SELECT DISTINCT xyz FROM ... ORDER BY xyz
**
** is transformed to:
**
** SELECT xyz FROM ... GROUP BY xyz ORDER BY xyz
**
** The second form is preferred as a single index (or temp-table) may be
** used for both the ORDER BY and DISTINCT processing. As originally
** written the query must use a temp-table for at least one of the ORDER
** BY and DISTINCT, and an index or separate temp-table for the other.
*/
if( (p->selFlags & (SF_Distinct|SF_Aggregate))==SF_Distinct
&& sqlite3ExprListCompare(sSort.pOrderBy, p->pEList, -1)==0
){
p->selFlags &= ~SF_Distinct;
p->pGroupBy = sqlite3ExprListDup(db, p->pEList, 0);
pGroupBy = p->pGroupBy;
/* Notice that even thought SF_Distinct has been cleared from p->selFlags,
** the sDistinct.isTnct is still set. Hence, isTnct represents the
** original setting of the SF_Distinct flag, not the current setting */
assert( sDistinct.isTnct );
}
/* If there is an ORDER BY clause, then this sorting
|
Changes to test/distinct.test.
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SELECT DISTINCT
CASE a WHEN 1 THEN x'0000000000'
WHEN 2 THEN zeroblob(5)
ELSE 'xyzzy' END
FROM t1;
SELECT quote(x) FROM t2 ORDER BY 1;
} {'xyzzy' X'0000000000'}
finish_test
|
> > > > > > > > > > > > > > > > > > > > > > > > > > > > > > |
217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 |
SELECT DISTINCT
CASE a WHEN 1 THEN x'0000000000'
WHEN 2 THEN zeroblob(5)
ELSE 'xyzzy' END
FROM t1;
SELECT quote(x) FROM t2 ORDER BY 1;
} {'xyzzy' X'0000000000'}
#----------------------------------------------------------------------------
# Ticket [c5ea805691bfc4204b1cb9e9aa0103bd48bc7d34] (2014-12-04)
# Make sure that DISTINCT works together with ORDER BY and descending
# indexes.
#
do_execsql_test 5.1 {
DROP TABLE IF EXISTS t1;
CREATE TABLE t1(x);
INSERT INTO t1(x) VALUES(3),(1),(5),(2),(6),(4),(5),(1),(3);
CREATE INDEX t1x ON t1(x DESC);
SELECT DISTINCT x FROM t1 ORDER BY x ASC;
} {1 2 3 4 5 6}
do_execsql_test 5.2 {
SELECT DISTINCT x FROM t1 ORDER BY x DESC;
} {6 5 4 3 2 1}
do_execsql_test 5.3 {
SELECT DISTINCT x FROM t1 ORDER BY x;
} {1 2 3 4 5 6}
do_execsql_test 5.4 {
DROP INDEX t1x;
CREATE INDEX t1x ON t1(x ASC);
SELECT DISTINCT x FROM t1 ORDER BY x ASC;
} {1 2 3 4 5 6}
do_execsql_test 5.5 {
SELECT DISTINCT x FROM t1 ORDER BY x DESC;
} {6 5 4 3 2 1}
do_execsql_test 5.6 {
SELECT DISTINCT x FROM t1 ORDER BY x;
} {1 2 3 4 5 6}
finish_test
|