MySQL Interview Questions [StartupCTO]

Last Updated: 28 Jun 2023

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Author: dordal

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= MySQL Interview Questions =
 * Explain the basic CRUD operations (CREATE, UPDATE, DELETE) and how you'd use SQL to perform them.
 * Explain the ''WHERE'' clause on a ''SELECT'' statement, what it does and how it works.
 * Explain ''GROUP BY''. What does it do, and when do you have to use it?
 * What is a view? Why would you want to use one?
 * What is a trigger? Why are triggers good and bad?
 * What's an index? Advanced: What are the different types of indexes?
 * What's a foreign key? What does the ''ON CASCADE'' clause do when creating a foreign key?
 * Explain what a transaction is, when you'd want to use one, and when you probably //wouldn't// want to use one.
 * Explain the MySQL architecture (e.g. the three layers... networking/connection layer, query parsing, and the storage engine)
 * Explain the differences between InnoDB and MyISAM. When would you want to use each?
 * Talk to me about the process you'd use for optimizing an SQL query. 
 * What's the difference between ''CHAR'', ''VARCHAR'', ''TEXT'' and ''BLOB'' datatypes?
 * Is there anything special about ''NULL'' values in MySQL (or SQL in general?) How do you test for a ''NULL'' value?
 * What's the difference between a ''TIMESTAMP'' field and a ''DATETIME'' field? Advanced question: can you describe the different handling of timezones between ''TIMESTAMP'' and ''DATETIME''?
 * Explain locking principles in MySQL. Table level locks, page-level locks, and row-level locks. Which storage engines can do which? Explain what [[http://dev.mysql.com/doc/refman/5.0/en/innodb-lock-modes.html|shared vs. exclusive locks]] are.
 * Why does ''DELETE FROM `mytable`'' run very quickly, whereas ''DELETE FROM `mytable` WHERE 1=1'' run very slowly, if 'mytable' has a large number of records? (e.g. the former just deletes and recreates the table on disk, whereas the latter will delete each row one-by-one.)

== PHP/MySQL Questions ==
 * Explain the difference between the standard MySQL libraries (e.g. mysql_connect() ) and the MySQLi libraries (e.g. mysqli_connect() ) 
 * Walk me through the basic process for connecting to a MySQL database and querying some information.

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