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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/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 ...
https://dev.mysql.com/doc/refman/5.7/en/server-options.html
--safe-user-create Command-Line Format --safe-user-create[={OFF|ON}] Type Boolean Default Value OFF If this option is enabled, a user cannot create new MySQL users by using the GRANT statement unless the user has the INSERT privilege for the ...
https://dev.mysql.com/doc/refman/5.7/en/string-comparison-functions.html
For example, it can be specified as a string expression or table column. In the latter case, the column must be defined as one of the MySQL string types (see Section 11.3, “String Data Types”). Note Aggregate queries involving NOT LIKE ... Table ...
https://dev.mysql.com/doc/refman/5.7/en/subqueries.html
Here is an example of a subquery: SELECT * FROM t1 WHERE column1 = (SELECT column1 FROM t2); In this example, SELECT * FROM t1 ... is the outer query (or outer statement), and (SELECT column1 FROM t2) is the subquery. All subquery forms and ...