What is Key_len in MySQL explain?

The key_len column indicates the length of the key that MySQL decided to use. The value of key_len enables you to determine how many parts of a multiple-part key MySQL actually uses. … The ref column shows which columns or constants are compared to the index named in the key column to select rows from the table.

What is filtered in explain?

The filtered column indicates an estimated percentage of table rows that will be filtered by the table condition. That is, rows shows the estimated number of rows examined and rows × filtered / 100 shows the number of rows that will be joined with previous tables.

What is profiling in MySQL?

mysql> SET profiling = 1; SHOW PROFILES displays a list of the most recent statements sent to the server. The size of the list is controlled by the profiling_history_size session variable, which has a default value of 15. The maximum value is 100. Setting the value to 0 has the practical effect of disabling profiling.

What is REF IN explain MySQL?

ref – Shows the columns or constants that are compared to the index named in the key column. MySQL will either pick a constant value to be compared or a column itself based on the query execution plan. You can see this in the example given below.

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What is the use of explain in MySQL?

The EXPLAIN keyword is used throughout various SQL databases and provides information about how your SQL database executes a query. In MySQL, EXPLAIN can be used in front of a query beginning with SELECT , INSERT , DELETE , REPLACE , and UPDATE .

What is filter and types?

Filters can be active or passive, and the four main types of filters are low-pass, high-pass, band-pass, and notch/band-reject (though there are also all-pass filters). I hope you’ve learned a bit about how to describe filters and what they can accomplish.

What is filter explain with example?

The most common filter is a software filter that reads data in and manipulates the data to fit another output pattern or removes data that may not be needed. For example, spam filters help filter unwanted e-mail from reaching your Inbox. 2. Hardware devices can also be filters.

How do you analyze in MySQL?

EXPLAIN ANALYZE is a profiling tool for your queries that will show you where MySQL spends time on your query and why. It will plan the query, instrument it and execute it while counting rows and measuring time spent at various points in the execution plan.

How do I trace a MySQL query?

How to show the queries log in MySQL?

  1. Enable Query logging on the database. SET global general_log = 1; SET global log_output = ‘table’;
  2. Now you can view the log by running this query: SELECT * FROM mysql. general_log;
  3. If you want to disable query logging on the database, run this query: SET global general_log = 0;
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What is MySQL performance tuning?

Software MySQL Performance Tuning. SQL performance tuning is the process of maximizing query speeds on a relational database. The task usually involves multiple tools and techniques. … Tweaking the MySQL configuration files. Writing more efficient database queries.

How interpret MySQL explain?

The EXPLAIN statement provides information about how MySQL executes statements:

  1. EXPLAIN works with SELECT , DELETE , INSERT , REPLACE , and UPDATE statements.
  2. When EXPLAIN is used with an explainable statement, MySQL displays information from the optimizer about the statement execution plan.

What is Filesort in MySQL?

In MySQL, filesort is the catch-all algorithm for producing sorted results for ORDER-BY or GROUP-BY queries. … The most commonly used algorithm is the so called modified algorithm, it is used for all cases except when BLOB and TEXT column are involved.

What are the features of MySQL?

The following are the most important features of MySQL:

  • Relational Database Management System (RDBMS) MySQL is a relational database management system. …
  • Easy to use. MySQL is easy to use. …
  • It is secure. …
  • Client/ Server Architecture. …
  • Free to download. …
  • It is scalable. …
  • Speed. …
  • High Flexibility.

What is your query means?

1 : to ask questions of especially with a desire for authoritative information. 2 : to ask questions about especially in order to resolve a doubt. 3 : to put as a question. 4 : to mark with a query.

How do you use explain?

We use the verb explain to mean ‘make something clear or easy to understand, by describing or giving information about it‘. We can use explain with a direct object or with a direct object and a prepositional phrase with to (direct objects are underlined): Could you explain this diagram, please?

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