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What happens when explain is used in MySQL?
When EXPLAIN is used with an explainable statement, MySQL displays information from the optimizer about the statement execution plan. That is, MySQL explains how it would process the statement, including information about how tables are joined and in which order. For…
When to use the explain keyword 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. For a simple query, it would look like the following:
What does a query look like in MySQL?
For a simple query, it would look like the following: Instead of the usual result output, MySQL would then show its statement execution plan by explaining which processes take place in which order when executing the statement.
Which is the first table accessed in MySQL?
As you can see in the EXPLAIN, the table votes is the first table accessed, using the ALL access_type, which means MySQL will scan the entire table, using no indexes, so it will go through over 14 million records. The posts table is then accessed using the eq_ref access type.
How does a transaction block reduce performance in SQL Server?
AS Seconds_WithTransaction Seconds_NoTransaction Seconds_WithTransaction 2.63200000 2.70400000 2.16700000 2.12300000
How does explain work in the MySQL optimizer?
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. That is, MySQL explains how it would process the statement, including information about how tables are joined and in which order.
When to run analyze TABLE statement in MySQL?
If you have a problem with indexes not being used when you believe that they should be, run ANALYZE TABLE to update table statistics, such as cardinality of keys, that can affect the choices the optimizer makes. See Section 13.7.2.1, “ANALYZE TABLE Statement” .
How does explain work in MySQL 8.0.19?
EXPLAIN works with SELECT, DELETE, INSERT, REPLACE, and UPDATE statements. In MySQL 8.0.19 and later, it also works with TABLE statements. When EXPLAIN is used with an explainable statement, MySQL displays information from the optimizer about the statement execution plan.