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MDEV-3818: Query against view over IS tables worse than equivalent query without view

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Analysis:
The reason for the suboptimal plan when querying IS tables through a view
was that the view columns that participate in an equality are wrapped by
an Item_direct_view_ref and were not recognized as being direct column
references.

Solution:
Use the original Item_field objects via the real_item() method.
This commit is contained in:
unknown 2012-12-17 15:23:58 +02:00
parent a334e87d65
commit d7a0148758
3 changed files with 41 additions and 3 deletions
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20
mysql-test/r/information_schema.result
View File

@ -1934,6 +1934,26 @@ event_object_table trigger_name
# Switching to connection 'default'.
#
#
# MDEV-3818: Query against view over IS tables worse than equivalent query without view
#
CREATE VIEW v1 AS SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS;
explain extended
SELECT column_name FROM v1
WHERE (TABLE_SCHEMA = "osm") AND (TABLE_NAME = "test");
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE COLUMNS ALL NULL TABLE_SCHEMA,TABLE_NAME NULL NULL NULL NULL Using where; Open_frm_only; Scanned 0 databases
Warnings:
Note 1003 select `information_schema`.`COLUMNS`.`COLUMN_NAME` AS `COLUMN_NAME` from `INFORMATION_SCHEMA`.`COLUMNS` where ((`information_schema`.`COLUMNS`.`TABLE_SCHEMA` = 'osm') and (`information_schema`.`COLUMNS`.`TABLE_NAME` = 'test'))
explain extended
SELECT INFORMATION_SCHEMA.COLUMNS.COLUMN_NAME AS COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE (information_schema.COLUMNS.TABLE_SCHEMA = 'osm') and (information_schema.COLUMNS.TABLE_NAME = 'test');
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE COLUMNS ALL NULL TABLE_SCHEMA,TABLE_NAME NULL NULL NULL NULL Using where; Open_frm_only; Scanned 0 databases
Warnings:
Note 1003 select `information_schema`.`COLUMNS`.`COLUMN_NAME` AS `COLUMN_NAME` from `INFORMATION_SCHEMA`.`COLUMNS` where ((`information_schema`.`COLUMNS`.`TABLE_SCHEMA` = 'osm') and (`information_schema`.`COLUMNS`.`TABLE_NAME` = 'test'))
drop view v1;
#
# Clean-up.
drop database mysqltest;
#

18
mysql-test/t/information_schema.test
View File

@ -1789,6 +1789,24 @@ disconnect con12828477_1;
disconnect con12828477_2;
disconnect con12828477_3;
--echo #
--echo # MDEV-3818: Query against view over IS tables worse than equivalent query without view
--echo #
CREATE VIEW v1 AS SELECT TABLE_SCHEMA, TABLE_NAME, COLUMN_NAME FROM INFORMATION_SCHEMA.COLUMNS;
explain extended
SELECT column_name FROM v1
WHERE (TABLE_SCHEMA = "osm") AND (TABLE_NAME = "test");
explain extended
SELECT INFORMATION_SCHEMA.COLUMNS.COLUMN_NAME AS COLUMN_NAME
FROM INFORMATION_SCHEMA.COLUMNS
WHERE (information_schema.COLUMNS.TABLE_SCHEMA = 'osm') and (information_schema.COLUMNS.TABLE_NAME = 'test');
drop view v1;
--echo #
--echo # Clean-up.
drop database mysqltest;

6
sql/sql_show.cc
View File

@ -3184,13 +3184,13 @@ bool get_lookup_value(THD *thd, Item_func *item_func,
Item_field *item_field;
CHARSET_INFO *cs= system_charset_info;
if (item_func->arguments()[0]->type() == Item::FIELD_ITEM &&
if (item_func->arguments()[0]->real_item()->type() == Item::FIELD_ITEM &&
item_func->arguments()[1]->const_item())
{
idx_field= 0;
idx_val= 1;
}
else if (item_func->arguments()[1]->type() == Item::FIELD_ITEM &&
else if (item_func->arguments()[1]->real_item()->type() == Item::FIELD_ITEM &&
item_func->arguments()[0]->const_item())
{
idx_field= 1;
@ -3199,7 +3199,7 @@ bool get_lookup_value(THD *thd, Item_func *item_func,
else
return 0;
item_field= (Item_field*) item_func->arguments()[idx_field];
item_field= (Item_field*) item_func->arguments()[idx_field]->real_item();
if (table->table != item_field->field->table)
return 0;
tmp_str= item_func->arguments()[idx_val]->val_str(&str_buff);