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https://dev.mysql.com/doc/refman/5.7/en/performance-schema-setup-timers-table.html
The value can be any of the values in the performance_timers.TIMER_NAME column. The setup_timers table has these columns: NAME The type of instrument the timer is used for. The setup_timers.TIMER_NAME value can be changed to select a different timer. For an explanation of how event timing occurs, see Section 25.4.1, “Performance Schema Event ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-system-variables.html
performance_schema_max_sql_text_length Command-Line Format --performance-schema-max-sql-text-length=# System Variable performance_schema_max_sql_text_length Scope Global Dynamic No Type Integer Default Value 1024 Minimum Value 0 Maximum Value ...The ...
https://dev.mysql.com/doc/refman/5.7/en/performance-schema-table-characteristics.html
Some of the setup tables have columns that can be modified to affect Performance Schema operation; some also permit rows to be inserted or deleted. Generally, the effect is to reset the summary columns to 0 or NULL, not to remove rows. To change ...
https://dev.mysql.com/doc/refman/5.7/en/precision-math-examples.html
Rounding for exact-value columns (DECIMAL and integer) and exact-valued numbers uses the “round half away from zero” rule. In strict mode, inserting a value that is out of range for a column causes an error, rather than truncation to a legal ...
https://dev.mysql.com/doc/refman/5.7/en/problems-with-float.html
For DECIMAL columns, MySQL performs operations with a precision of 65 decimal digits, which should solve most common inaccuracy problems. If columns d1 and d2 had been defined as DECIMAL rather than DOUBLE, the result of the SELECT query would have ... Floating-point numbers sometimes cause confusion because they are approximate and not stored as exact ...
https://dev.mysql.com/doc/refman/5.7/en/program-options.html
The following command runs mysql in “no column names” mode: mysql --column-names --skip-column-names MySQL programs determine which options are given first by examining environment variables, then by processing option files, and then by checking ... There are several ways to specify options for MySQL programs: List the options on the command line following the program ...
https://dev.mysql.com/doc/refman/5.7/en/replication-features-reserved-words.html
An example of this is using a table column named virtual on a 5.6 source that is replicating to a 5.7 or higher replica because VIRTUAL is a reserved word beginning in MySQL 5.7. Replication can fail in such cases with Error 1064 You have an error ... You can encounter problems when you attempt to replicate from an older source to a newer replica and you make use of identifiers on the source that are reserved words in the newer MySQL version running on the ...
https://dev.mysql.com/doc/refman/5.7/en/replication-rbr-safe-unsafe.html
Trigger or stored program updates a table having an AUTO_INCREMENT column. In addition, an INSERT into a table that has a composite primary key containing an AUTO_INCREMENT column that is not the first column of this composite key is unsafe. The ...
https://dev.mysql.com/doc/refman/5.7/en/row-constructor-optimization.html
For example, these two statements are semantically equivalent: SELECT * FROM t1 WHERE (column1,column2) = (1,1); SELECT * FROM t1 WHERE column1 = 1 AND column2 = 1; In addition, the optimizer handles both expressions the same way. The optimizer is ...However, the row constructor itself does not cover an index prefix, with the result that the optimizer uses only c1 (key_len=4, the size of c1): mysql> EXPLAIN SELECT * FROM t1 WHERE c1=1 AND (c2,c3) > (1,1)\G *************************** ...
https://dev.mysql.com/doc/refman/5.7/en/scalar-subqueries.html
A scalar subquery is a simple operand, and you can use it almost anywhere a single column value or literal is legal, and you can expect it to have those characteristics that all operands have: a data type, a length, an indication that it can be ...