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##
## Use 'irrational' joins to compare columns longer than the key length of the index.
##
USE performance_schema;
## HA_KEY_TYPE_TEXT
## users.user char(32) vs. hosts.host char(60)
EXPLAIN SELECT * FROM (users AS t1 INNER JOIN hosts AS t2 ON (t2.host = t1.user));
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t2 NULL ALL HOST NULL NULL NULL # 100.00 Using where
1 SIMPLE t1 NULL eq_ref USER USER 129 performance_schema.t2.HOST # 100.00 Using where
Warnings:
Warning 1739 Cannot use ref access on index 'HOST' due to type or collation conversion on field 'HOST'
Note 1003 /* select#1 */ select `performance_schema`.`t1`.`USER` AS `USER`,`performance_schema`.`t1`.`CURRENT_CONNECTIONS` AS `CURRENT_CONNECTIONS`,`performance_schema`.`t1`.`TOTAL_CONNECTIONS` AS `TOTAL_CONNECTIONS`,`performance_schema`.`t1`.`MAX_SESSION_CONTROLLED_MEMORY` AS `MAX_SESSION_CONTROLLED_MEMORY`,`performance_schema`.`t1`.`MAX_SESSION_TOTAL_MEMORY` AS `MAX_SESSION_TOTAL_MEMORY`,`performance_schema`.`t2`.`HOST` AS `HOST`,`performance_schema`.`t2`.`CURRENT_CONNECTIONS` AS `CURRENT_CONNECTIONS`,`performance_schema`.`t2`.`TOTAL_CONNECTIONS` AS `TOTAL_CONNECTIONS`,`performance_schema`.`t2`.`MAX_SESSION_CONTROLLED_MEMORY` AS `MAX_SESSION_CONTROLLED_MEMORY`,`performance_schema`.`t2`.`MAX_SESSION_TOTAL_MEMORY` AS `MAX_SESSION_TOTAL_MEMORY` from `performance_schema`.`users` `t1` join `performance_schema`.`hosts` `t2` where (`performance_schema`.`t2`.`HOST` = `performance_schema`.`t1`.`USER`)
SELECT COUNT(*) FROM (users AS t1 INNER JOIN hosts AS t2 ON (t2.host = t1.user));
COUNT(*)
#
## HA_KEY_TYPE_VARCHAR1 or HA_KEY_TYPE_VARCHAR2
## file_instances.file_name varchar(512) vs. session_variables.variable_name varchar(1024)
EXPLAIN SELECT * FROM (file_instances AS t1 INNER JOIN session_variables AS t2 ON (t2.variable_value = t1.file_name));
id select_type table partitions type possible_keys key key_len ref rows filtered Extra
1 SIMPLE t2 NULL ALL NULL NULL NULL NULL # 100.00 Using where
1 SIMPLE t1 NULL eq_ref PRIMARY PRIMARY 2050 performance_schema.t2.VARIABLE_VALUE # 100.00 Using where
Warnings:
Note 1003 /* select#1 */ select `performance_schema`.`t1`.`FILE_NAME` AS `FILE_NAME`,`performance_schema`.`t1`.`EVENT_NAME` AS `EVENT_NAME`,`performance_schema`.`t1`.`OPEN_COUNT` AS `OPEN_COUNT`,`performance_schema`.`t2`.`VARIABLE_NAME` AS `VARIABLE_NAME`,`performance_schema`.`t2`.`VARIABLE_VALUE` AS `VARIABLE_VALUE` from `performance_schema`.`file_instances` `t1` join `performance_schema`.`session_variables` `t2` where (`performance_schema`.`t2`.`VARIABLE_VALUE` = `performance_schema`.`t1`.`FILE_NAME`)
SELECT COUNT(*) FROM (file_instances AS t1 INNER JOIN session_variables AS t2 ON (t2.variable_value = t1.file_name));
COUNT(*)
#
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