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Question & Answer of MySql  Back
What Is MySQL?

MySQL is an open source database management system developed by MySQL AB
What Is Primary Key?

A primary key is a single column or multiple columns defined to have unique values that can be used as row identifications.
What Is Foreign Key?

A foreign key is a single column or multiple columns defined to have values that can be mapped to a primary key in another table.
What Is Index?

An index is a single column or multiple columns defined to have values pre-sorted to speed up data retrieval speed.
What Is Join?

Join is data retrieval operation that combines rows from multiple tables under certain matching conditions to form a single row.
What Is Transaction?

A transaction is a logical unit of work requested by a user to be applied to the database objects. MySQL server introduces the transaction concept to allow users to group one or more SQL statements into a single transaction, so that the effects of all the SQL statements in a transaction can be either all committed (applied to the database) or all rolled back (undone from the database).
What Is Commit?

Commit is a way to terminate a transaction with all database changes to be saved permanently to the database server.
What Is MyISAM?

MyISAM is a storage engine used as the default storage engine for MySQL database. MyISAM is based on the ISAM (Indexed Sequential Access Method) concept and offers fast data storage and retrieval. But it is not transaction safe.
If the value in the column is repeatable, how do you find out the unique values? 

sUse DISTINCT in the query, such as SELECT DISTINCT user_firstname FROM users; You can also ask for a number of distinct values by saying SELECT COUNT (DISTINCT user_firstname) FROM users.
When would you use ORDER BY in DELETE statement? 

When you’re not deleting by row ID. Such as in DELETE FROM table_question ORDER BY timestamp LIMIT 1. This will delete the most recently posted question in the table techinterviews_com_questions.
What’s the difference between CHAR_LENGTH and LENGTH? 

The first is, naturally, the character count. The second is byte count. For the Latin characters the numbers are the same, but they’re not the same for Unicode and other encodings.