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https://dev.mysql.com/doc/refman/8.0/en/subquery-optimization.html
Note A limitation on UPDATE and DELETE statements that use a subquery to modify a single table is that the optimizer does not use semijoin or materialization subquery optimizations. As a workaround, try rewriting them as multiple-table UPDATE and ...
https://dev.mysql.com/doc/refman/8.0/en/table-corruption.html
If you have started mysqld with the myisam_recover_options system variable set, MySQL automatically checks and tries to repair MyISAM tables if they are marked as 'not closed properly' or 'crashed'. If this happens, MySQL writes an entry in the ...
https://dev.mysql.com/doc/refman/8.0/en/binary-log.html
The binary log contains “events” that describe database changes such as table creation operations or changes to table data. This is done to ensure that you can re-create an exact copy of your tables by applying the log during a backup operation. The number increases each time the server creates a new log file, thus creating an ordered series of ...It also contains events for statements that ...
https://dev.mysql.com/doc/refman/8.0/en/charset-column.html
CREATE TABLE t1 ( col1 CHAR(10) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci ) CHARACTER SET latin1 COLLATE latin1_bin; The character set and collation are specified for the column, so they are used. CREATE TABLE t1 ( col1 CHAR(10) CHARACTER SET ...To see the default collation for each character set, use the SHOW CHARACTER SET statement or query the INFORMATION_SCHEMA CHARACTER_SETS ... Every ...
https://dev.mysql.com/doc/refman/8.0/en/select-into.html
SELECT id, data INTO @x, @y FROM test.t1 LIMIT 1; INTO var_list can also be used with a TABLE statement, subject to these restrictions: The number of variables must match the number of columns in the table. If the table contains more than one row, ...INTO form of SELECT enables a query result to be stored in variables or written to a file: SELECT ...
https://dev.mysql.com/doc/refman/8.0/en/myisamchk-check-options.html
myisamchk supports the following options for table checking operations: --check, -c Command-Line Format --check Check the table for errors. --check-only-changed, -C Command-Line Format --check-only-changed Check only tables that have changed since ...This is the default operation if you specify no option that selects an operation type ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-ndb-transid-mysql-connection-map-table.html
For this table to be created, the MySQL Server must be a binary supplied with the NDB Cluster distribution, or one built from the NDB Cluster sources with NDB storage engine support enabled. The ndb_transid_mysql_connection_map table provides a ...
https://dev.mysql.com/doc/refman/8.0/en/optimizing-memory-tables.html
Consider using MEMORY tables for noncritical data that is accessed often, and is read-only or rarely updated. Benchmark your application against equivalent InnoDB or MyISAM tables under a realistic workload, to confirm that any additional ...B-tree ...
https://dev.mysql.com/doc/refman/8.0/en/column-indexes.html
For example: CREATE TABLE test (blob_col BLOB, INDEX(blob_col(10))); Prefixes can be up to 767 bytes long for InnoDB tables that use the REDUNDANT or COMPACT row format. Note Prefix limits are measured in bytes, whereas the prefix length in CREATE ...The maximum number of indexes per table and the maximum index length is defined per storage ... The most common type of index involves a single column, storing copies of the values from that ...
https://dev.mysql.com/doc/refman/8.0/en/ddl-rewriter.html
MySQL 8.0.16 and higher includes a ddl_rewriter plugin that modifies CREATE TABLE statements received by the server before it parses and executes them. The plugin removes ENCRYPTION, DATA DIRECTORY, and INDEX DIRECTORY clauses, which may be helpful ...Within statements considered for rewrite, instances of the following clauses are rewritten and each instance replaced by a single space: ENCRYPTION DATA DIRECTORY (at the table and partition levels) INDEX DIRECTORY (at the table and partition levels) Rewriting does not depend on ...