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https://dev.mysql.com/doc/refman/8.0/en/subquery-optimization-with-exists.html
This is a problem because many real world subqueries become very slow unless the equality can be pushed down. For multiple-table subqueries, execution of NULL IN (SELECT ...) is particularly slow because the join optimizer does not optimize for the ...WHERE subquery_where) MySQL evaluates queries “from outside to inside.” That is, it first obtains the value of the outer expression outer_expr, and then runs the subquery and captures the rows that it ...
https://dev.mysql.com/doc/refman/8.0/en/information-schema-optimization.html
To write queries for these tables most efficiently, use the following general guidelines: Try to query only INFORMATION_SCHEMA tables that are views on data dictionary tables. Note Comparison behavior for database and table names in ... Applications ...
https://dev.mysql.com/doc/refman/8.0/en/limit-optimization.html
If you need only a specified number of rows from a result set, use a LIMIT clause in the query, rather than fetching the whole result set and throwing away the extra data. MySQL sometimes optimizes a query that has a LIMIT row_count clause and no ...
https://dev.mysql.com/doc/refman/8.0/en/performance-schema-optimization.html
To write queries for these tables most efficiently, take advantage of their indexes. Tables that do not are those that normally contain few rows or are unlikely to be queried frequently. Applications that monitor databases may make frequent use of ...
https://dev.mysql.com/doc/refman/8.0/en/execution-plan-information.html
Depending on the details of your tables, columns, indexes, and the conditions in your WHERE clause, the MySQL optimizer considers many techniques to efficiently perform the lookups involved in an SQL query. A query on a huge table can be performed ...
https://dev.mysql.com/doc/refman/8.0/en/controlling-optimizer.html
MySQL provides optimizer control through system variables that affect how query plans are evaluated, switchable optimizations, optimizer and index hints, and the optimizer cost model. The server maintains histogram statistics about column values in ...
https://dev.mysql.com/doc/refman/8.0/en/estimating-performance.html
The preceding discussion does not mean that your application performance slowly degenerates by log N. As long as everything is cached by the OS or the MySQL server, things become only marginally slower as the table gets bigger. After the data gets ... In most cases, you can estimate query performance by counting disk ...
https://dev.mysql.com/doc/refman/8.0/en/replication-features-optimizer.html
It is possible for the data on the source and replica to become different if a statement is written in such a way that the data modification is nondeterministic; that is, left up the query optimizer. (In general, this is not a good practice, even ...
https://dev.mysql.com/doc/refman/8.0/en/using-explain.html
The EXPLAIN statement provides information about how MySQL executes statements: EXPLAIN works with SELECT, DELETE, INSERT, REPLACE, and UPDATE statements. When EXPLAIN is used with an explainable statement, MySQL displays information from the ...
https://dev.mysql.com/doc/refman/8.0/en/examples.html
Here are examples of how to solve some common problems with MySQL. Some of the examples use the table shop to hold the price of each article (item number) for certain traders (dealers). Supposing that each trader has a single fixed price per ...