keys : indicates the actual index used by MySQL. MySQL always looks for an optimal key that can be used for the query. While joining many tables, it may figure out some other keys which are not listed in possible_keys but are more optimal. key_len : indicates the length of the index the query optimizer chose to use.
What is explain command in MySQL?
The EXPLAIN statement provides information about how MySQL executes statements. EXPLAIN works with SELECT , DELETE , INSERT , REPLACE , and UPDATE statements. … That is, MySQL explains how it would process the statement, including information about how tables are joined and in which order.
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 Key_len in MySQL explain?
mysql. According to MySQL website, the key_len column indicates the length of the key that MySQL decided to use. The length is NULL if the key column says NULL . Note that the value of key_len enables you to determine how many parts of a multiple-part key MySQL actually uses.
What does the key column of explain output indicate?
The key column in the output row indicates which index is used. … An index-only scan usually is faster than ALL because the size of the index usually is smaller than the table data. A full table scan is performed using reads from the index to look up data rows in index order.
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.
What is MySQL used for?
MySQL is a relational database management system based on SQL – Structured Query Language. The application is used for a wide range of purposes, including data warehousing, e-commerce, and logging applications. The most common use for mySQL however, is for the purpose of a web database.
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.
What is SQL and examples?
SQL is an ANSI and ISO standard, and is the de facto standard database query language. A variety of established database products support SQL, including products from Oracle and Microsoft SQL Server. It is widely used in both industry and academia, often for enormous, complex databases.
How does MySQL query work?
mysql displays query output in tabular form (rows and columns). The first row contains labels for the columns. The rows following are the query results. Normally, column labels are the names of the columns you fetch from database tables.
What is MySQL language?
MySQL is a relational database management system (RDBMS) developed by Oracle that is based on structured query language (SQL). A database is a structured collection of data. It may be anything from a simple shopping list to a picture gallery or a place to hold the vast amounts of information in a corporate network.
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 indexes MySQL?
Indexes are used to find rows with specific column values quickly. Without an index, MySQL must begin with the first row and then read through the entire table to find the relevant rows. The larger the table, the more this costs. … MySQL uses indexes for these operations: To find the rows matching a WHERE clause quickly.
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.
What is analyze table in MySQL?
ANALYZE TABLE performs a key distribution analysis and stores the distribution for the named table or tables. For MyISAM tables, this statement is equivalent to using myisamchk –analyze. This statement requires SELECT and INSERT privileges for the table. ANALYZE TABLE works with InnoDB , NDB , and MyISAM tables.
What does the command Explain do?
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.