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Mark constant 'null_tables' with table->const_table=1

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This was done to make thing consistent. It gives the additional benefit
that EXPLAIN EXTENDED now treat null_tables like constant's and replaces
columns with NULL, in a similar way that it replaces columns with constants
for constant tables.

- Null tables are tables where all columns are always NULL. The most common
  NULL TABLE is a table used in a LEFT_JOIN that is never true.
- All result changes comes from replacing columns with NULL for null_tables.
- "Impossible where" is now also shows constants for const columns.
- Removed duplicated s->type= JT_CONST
- Reset found_const_table_map when JOIN is created (safety fix)
This commit is contained in:
Monty
2017-11-30 17:01:23 +02:00
parent ddac2d7a1e
commit c65911ac46
10 changed files with 15 additions and 11 deletions
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2
mysql-test/r/range.result
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@ -2284,7 +2284,7 @@ explain extended select * from t2 where (b > 25 and b < 15) or (a>55 and a<44);
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE NULL NULL NULL NULL NULL NULL NULL NULL Impossible WHERE noticed after reading const tables
Warnings:
Note 1003 select `test`.`t2`.`a` AS `a`,`test`.`t2`.`b` AS `b`,`test`.`t2`.`c` AS `c` from `test`.`t2` where 0
Note 1003 select 44 AS `a`,15 AS `b`,NULL AS `c` from `test`.`t2` where 0
drop table t1,t2;
#
# Start of 10.1 tests