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https://dev.mysql.com/doc/refman/5.7/en/problems-with-null.html
The concept of the NULL value is a common source of confusion for newcomers to SQL, who often think that NULL is the same thing as an empty string ''. For example, the following statements are completely different: mysql> INSERT INTO my_table ...In ...
https://dev.mysql.com/doc/refman/5.7/en/truncate-table.html
TRUNCATE TABLE can be used with Performance Schema summary tables, but the effect is to reset the summary columns to 0 or NULL, not to remove rows. To achieve high performance, it bypasses the DML method of deleting data. Thus, it cannot be rolled ...Logically, TRUNCATE TABLE is similar to a DELETE statement that deletes all rows, or a sequence of DROP TABLE and CREATE TABLE ...
https://dev.mysql.com/doc/refman/5.7/en/myisampack.html
--character-sets-dir=dir_name Command-Line Format --character-sets-dir=dir_name Type Directory name The directory where character sets are installed. When the table is used later, the server reads into memory the information needed to decompress ...
https://dev.mysql.com/doc/refman/5.7/en/connection-compression-control.html
Because enabling compression decreases performance, its benefits occur primarily when there is low network bandwidth, network transfer time dominates the cost of compression and decompression operations, and result sets are large. Compressed ...
https://dev.mysql.com/doc/refman/5.7/en/events-status-info.html
For statements that may retrieve multiple rows, another strategy is to use LIMIT 1 to limit the result set to a single row. The Event Scheduler writes information about event execution that terminates with an error or warning to the MySQL Server's ...INTO var_list statements, if the query returns no rows, a warning with error code 1329 occurs (No data), and the variable values remain ...
https://dev.mysql.com/doc/refman/5.7/en/group-replication-group-membership.html
In MySQL Group Replication, a set of servers forms a replication group. A group has a name, which takes the form of a UUID. If a server leaves the group, for instance it was taken down for maintenance, the remaining servers notice that it has left ...The group is dynamic and servers can leave (either voluntarily or involuntarily) and join it at any ...
https://dev.mysql.com/doc/refman/5.7/en/innodb-online-ddl-limitations.html
The ALTER TABLE clause LOCK=NONE is not permitted if there are ON...CASCADE or ON...SET NULL constraints on the table. Before an online DDL operation can finish, it must wait for transactions that hold metadata locks on the table to commit or roll ... The following limitations apply to online DDL operations: The table is copied when creating an index on a TEMPORARY ...
https://dev.mysql.com/doc/refman/5.7/en/view-algorithms.html
The optional ALGORITHM clause for CREATE VIEW or ALTER VIEW is a MySQL extension to standard SQL. For MERGE, the text of a statement that refers to the view and the view definition are merged such that parts of the view definition replace ...It ...
https://dev.mysql.com/doc/refman/5.7/en/functions.html
Rather than showing examples in this format: mysql> SELECT MOD(29,9); +-----------+ | mod(29,9) | +-----------+ | 2 | +-----------+ 1 rows in set (0.00 sec) This format is used instead: mysql> SELECT MOD(29,9); -> 2 . Expressions can be used at ...
https://dev.mysql.com/doc/refman/5.7/en/option-modifiers.html
The --maximum prefix is available for mysqld only and permits a limit to be placed on how large client programs can set session system variables. For example, with --maximum-back_log=200, the server produces this error: Maximum value of 'back_log' ...For example, the mysql client supports a --column-names option that determines whether or not to display a row of column names at the beginning of query ...