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bug #27531: 5.1 part of the fix:
- added join cache indication in EXPLAIN (Extra column). - prefer filesort over full scan over index for ORDER BY (because it's faster). - when switching from REF to RANGE because RANGE uses longer key turn off sort on the head table only as the resulting RANGE access is a candidate for join cache and we don't want to disable it by sorting on the first table only. mysql-test/r/archive_gis.result: bug #27531: join cache in EXPLAIN mysql-test/r/compress.result: bug #27531: - join cache in EXPLAIN. - prefer filesort over full scan over index for ORDER BY. mysql-test/r/ctype_utf8.result: bug #27531: join cache in EXPLAIN mysql-test/r/derived.result: bug #27531: join cache in EXPLAIN mysql-test/r/distinct.result: bug #27531: join cache in EXPLAIN mysql-test/r/func_group.result: bug #27531: join cache in EXPLAIN mysql-test/r/func_group_innodb.result: bug #27531: join cache in EXPLAIN mysql-test/r/gis.result: bug #27531: join cache in EXPLAIN mysql-test/r/greedy_optimizer.result: bug #27531: join cache in EXPLAIN mysql-test/r/group_by.result: bug #27531: join cache in EXPLAIN mysql-test/r/group_min_max.result: bug #27531: join cache in EXPLAIN mysql-test/r/index_merge_myisam.result: bug #27531: join cache in EXPLAIN mysql-test/r/information_schema.result: bug #27531: join cache in EXPLAIN mysql-test/r/innodb_gis.result: bug #27531: join cache in EXPLAIN mysql-test/r/innodb_mysql.result: bug #27531: join cache in EXPLAIN mysql-test/r/join.result: bug #27531: join cache in EXPLAIN mysql-test/r/join_nested.result: bug #27531: join cache in EXPLAIN mysql-test/r/key_diff.result: bug #27531: join cache in EXPLAIN mysql-test/r/myisam.result: bug #27531: join cache in EXPLAIN mysql-test/r/ndb_condition_pushdown.result: bug #27531: join cache in EXPLAIN mysql-test/r/ndb_gis.result: bug #27531: join cache in EXPLAIN mysql-test/r/range.result: bug #27531: join cache in EXPLAIN mysql-test/r/row.result: bug #27531: join cache in EXPLAIN mysql-test/r/select.result: bug #27531: - join cache in EXPLAIN. - prefer filesort over full scan over index for ORDER BY. mysql-test/r/ssl.result: bug #27531: - join cache in EXPLAIN. - prefer filesort over full scan over index for ORDER BY. mysql-test/r/ssl_compress.result: bug #27531: - join cache in EXPLAIN. - prefer filesort over full scan over index for ORDER BY. mysql-test/r/subselect.result: bug #27531: join cache in EXPLAIN mysql-test/r/subselect3.result: bug #27531: join cache in EXPLAIN mysql-test/r/union.result: bug #27531: join cache in EXPLAIN mysql-test/r/view.result: bug #27531: join cache in EXPLAIN sql/sql_select.cc: bug #27531: - join cache in EXPLAIN. - prefer filesort over full scan over index for ORDER BY. - disable sorting on the first table only when switching from REF to RANGE.
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@ -499,7 +499,7 @@ a b
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explain (select * from t1 where a=1 and b=10) union (select straight_join t1.a,t2.a from t1,t2 where t1.a=t2.a);
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id select_type table type possible_keys key key_len ref rows Extra
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1 PRIMARY NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
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2 UNION t1 index PRIMARY PRIMARY 4 NULL 4 Using index
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2 UNION t1 index PRIMARY PRIMARY 4 NULL 4 Using index; Using join cache
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2 UNION t2 index PRIMARY PRIMARY 4 NULL 4 Using where; Using index
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NULL UNION RESULT <union1,2> ALL NULL NULL NULL NULL NULL
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explain (select * from t1 where a=1) union (select * from t1 where b=1);
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