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https://dev.mysql.com/doc/refman/5.7/en/performance-schema-stage-tables.html
The Performance Schema instruments stages, which are steps during the statement-execution process, such as parsing a statement, opening a table, or performing a filesort operation. Stages correspond to the thread states displayed by SHOW ...
https://dev.mysql.com/doc/refman/5.7/en/row-subqueries.html
Scalar or column subqueries return a single value or a column of values. A row constructor is used for comparisons with subqueries that return two or more columns. A row subquery is a subquery variant that returns a single row and can thus return ...
https://dev.mysql.com/doc/refman/5.7/en/sql-prepared-statements.html
Typically, database applications process large volumes of almost-identical statements, with only changes to literal or variable values in clauses such as WHERE for queries and deletes, SET for updates, and VALUES for inserts. Using prepared ...
https://dev.mysql.com/doc/refman/5.7/en/sys-sys-config.html
Otherwise, it must be the name of an existing view that queries the Performance Schema events_statements_summary_by_digest table. This table contains sys schema configuration options, one row per option. Configuration changes made by updating this ...
https://dev.mysql.com/doc/refman/5.7/en/table-cache.html
MySQL is multithreaded, so there may be many clients issuing queries for a given table simultaneously. For example, for 200 concurrent running connections, specify a table cache size of at least 200 * N, where N is the maximum number of tables per ... When you execute a mysqladmin status command, you should see something like this: Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12 The Open tables value of 12 can be somewhat puzzling if you have fewer than 12 ...
https://dev.mysql.com/doc/refman/5.7/en/tracing-example.html
If a statement uses subqueries, there can be mutliple preparations, optimizations, and executions, as well as subquery-specific transformations. Now we can examine the trace, whose first column (QUERY), containing the original statement to be ...
https://dev.mysql.com/doc/refman/5.7/en/xa-states.html
An XA transaction progresses through the following states: Use XA START to start an XA transaction and put it in the ACTIVE state. For an ACTIVE XA transaction, issue the SQL statements that make up the transaction, and then issue an XA END ...
https://dev.mysql.com/doc/refman/5.7/en/aggregate-functions.html
This section describes aggregate functions that operate on sets of values. They are often used with a GROUP BY clause to group values into subsets. If you use an aggregate function in a statement containing no GROUP BY clause, it is equivalent to ...
https://dev.mysql.com/doc/refman/5.7/en/char.html
The CHAR and VARCHAR types are similar, but differ in the way they are stored and retrieved. They also differ in maximum length and in whether trailing spaces are retained. The CHAR and VARCHAR types are declared with a length that indicates the ...
https://dev.mysql.com/doc/refman/5.7/en/column-count-limit.html
This section describes limits on the number of columns in tables and the size of individual rows. Column Count Limits Row Size Limits Column Count Limits MySQL has hard limit of 4096 columns per table, but the effective maximum may be less for a ...