Details
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Bug
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Status: Closed (View Workflow)
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Major
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Resolution: Fixed
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10.1.21
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None
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linux
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10.1.22
Description
When having tables with unknown storage engine, e.g. due to a missing plugin, information for such tables is only read from INFORMATION_SCHEMA.TABLES on SELECT * FROM TABLES ...", not when trying to get the count of tables with SELECT COUNT(*) or when trying to read specific tables only. (found while trying to come up with a fix for MDEV-11942)
How to reproduce:
INSTALL SONAME 'ha_blackhole';
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CREATE TABLE test.t1 (id int primary key) ENGINE=BLACKHOLE;
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UNINSTALL PLUGIN BLACKHOLE;
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Now we have a table with unknown engine.
MariaDB [information_schema]> select * from tables where table_schema="test"\G
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*************************** 1. row ***************************
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TABLE_CATALOG: def
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TABLE_SCHEMA: test
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TABLE_NAME: t1
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TABLE_TYPE: BASE TABLE
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ENGINE: NULL
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VERSION: NULL
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ROW_FORMAT: NULL
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TABLE_ROWS: NULL
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AVG_ROW_LENGTH: NULL
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DATA_LENGTH: NULL
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MAX_DATA_LENGTH: NULL
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INDEX_LENGTH: NULL
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DATA_FREE: NULL
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AUTO_INCREMENT: NULL
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CREATE_TIME: NULL
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UPDATE_TIME: NULL
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CHECK_TIME: NULL
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TABLE_COLLATION: NULL
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CHECKSUM: NULL
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CREATE_OPTIONS: NULL
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TABLE_COMMENT: Unknown storage engine 'BLACKHOLE'
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1 row in set, 1 warning (0.00 sec)
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SELECT * found the table entry just fine and correctly reported the engine as unknown.
Now lets try to only read specific columns instead of '*'
MariaDB [information_schema]> select table_name, table_comment from tables where table_schema="test"\G
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Empty set (0.00 sec)
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The table is no longer found, but COUNT(*) works here:
MariaDB [information_schema]> select count(*) from tables where table_schema="test"\G
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*************************** 1. row ***************************
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count(*): 1
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1 row in set (0.00 sec)
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Now instead of searching by schema lets search by table comment instead:
MariaDB [information_schema]> select * from tables where table_comment like "Unknown storage engine %"\G
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*************************** 1. row ***************************
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TABLE_CATALOG: def
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TABLE_SCHEMA: test
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TABLE_NAME: t1
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TABLE_TYPE: BASE TABLE
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ENGINE: NULL
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VERSION: NULL
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ROW_FORMAT: NULL
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TABLE_ROWS: NULL
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AVG_ROW_LENGTH: NULL
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DATA_LENGTH: NULL
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MAX_DATA_LENGTH: NULL
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INDEX_LENGTH: NULL
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DATA_FREE: NULL
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AUTO_INCREMENT: NULL
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CREATE_TIME: NULL
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UPDATE_TIME: NULL
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CHECK_TIME: NULL
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TABLE_COLLATION: NULL
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CHECKSUM: NULL
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CREATE_OPTIONS: NULL
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TABLE_COMMENT: Unknown storage engine 'BLACKHOLE'
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1 row in set, 1 warning (0.01 sec)
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This worked, but asking for specific columns again doesn't:
MariaDB [information_schema]> select table_name, table_comment from tables where table_comment like "Unknown storage engine %"\G
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Empty set (0.00 sec)
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And now COUNT(*) doesn't work anymore either:
MariaDB [information_schema]> select count(*) from tables where table_comment like "Unknown storage engine %"\G
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*************************** 1. row ***************************
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count(*): 0
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1 row in set (0.01 sec)
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Expected result: changes in the filed list, but not on the WHERE condition, should not change the query results
Attachments
Issue Links
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- Closed
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