Often, the simplest fix and quickest advice is to add an index to a specific table’s columns in question if they are used in many queries with performance issues. While it can certainly help you, it will not take away the need for structural thinking and a good overview of the data models in place. Note: If EXPLAIN does not work for you, your database user might not have the SELECT privilege for the tables or views you are using in your statement.ĮXPLAIN is a great tool to quickly remedy slow queries. 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. For a simple query, it would look like the following: EXPLAIN SELECT * FROM foo WHERE foo.bar = 'infrastructure as a service' OR foo.bar = 'iaas' In MySQL, EXPLAIN can be used in front of a query beginning with SELECT, INSERT, DELETE, REPLACE, and UPDATE. The EXPLAIN keyword is used throughout various SQL databases and provides information about how your SQL database executes a query. Why are there 5 joins and why is there an ORDER BY used within a subquery before one of the joins even happens? Remember, you were hired for a reason - most likely, that reason also has to do with many convoluted queries that were created and edited over the last decade. You’re in your new job as Database Administrator or Data Engineer and you just got lost trying to figure out what these insane looking queries are supposed to mean and do.
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