What is ref in MySQL explain?

What is filtered in explain MySQL?

As described here in the MySQL docs: 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.

How read explain in MySQL?

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.

How do you explain a query?

A query is a request for data or information from a database table or combination of tables. This data may be generated as results returned by Structured Query Language (SQL) or as pictorials, graphs or complex results, e.g., trend analyses from data-mining tools.

How do you optimize MySQL query using explain?

Optimizing Database Schema

  1. Limiting the number of columns: MySQL has a limit of 4096 columns per table. …
  2. Normalize Tables: Normalizing keeps all data non-redundant. …
  3. Use the Most Appropriate Data Types: There are more than 20 different data types in MySQL designed for different uses. …
  4. Avoid Null Values.
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How do you use MySQL explain?

In MySQL, EXPLAIN can be used in front of a query beginning with SELECT , INSERT , DELETE , REPLACE , and UPDATE . For a simple query, it would look like the following: EXPLAIN SELECT * FROM foo WHERE foo. bar = ‘infrastructure as a service’ OR foo.

What is extra in explain MySQL?

Extra – contains additional information regarding the query execution plan. Values such as “Using temporary”, “Using filesort”, etc. in this column may indicate a troublesome query. For a complete list of possible values and their meaning, check out the MySQL documentation.

What is meant by MySQL?

MySQL (/ˌmaɪˌɛsˌkjuːˈɛl/) is an open-source relational database management system (RDBMS). … A relational database organizes data into one or more data tables in which data types may be related to each other; these relations help structure the data.

What is query in MySQL?

MySQL query is any command that used to retrieve the data from a table. MySQL can be used for querying the data, filtering data, sorting data, joining the tables, grouping data, modifying the data.

What is MySQL explain plan?

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 optimizer about the statement execution plan.

Which is an example of a query?

For example, if you need additional information from someone, you might say, “I have a query for you.” In computing, queries are also used to retrieve information. However, computer queries are sent to a computer system and are processed by a software program rather than a person.

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What is the use of a query?

Queries help you find and work with your data

A query can either be a request for data results from your database or for action on the data, or for both. A query can give you an answer to a simple question, perform calculations, combine data from different tables, add, change, or delete data from a database.

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