SQL UNION in MySQL

SQL LIKE allows you to perform pattern matching in your characters column in a database table. SQL LIKE is often used with SELECT statement in WHERE clause. MySQL provides you two wildcard characters for use with LIKE, the percentage % and underscore _.

?Percentage (%) wildcard allows you to match any string of zero or more characters
?Underscore (_) allows you to match any sing character.

In some cases, the information we need is not actually stored in the database but we can retrieve it by computing in some ways from stored data. For example, we have OrderDetails table to store order data, we don't know total of money of all selling products when we look at the table. In order to do so, we can use aggregate functions. By definition, aggregate functions allow us to perform a calculation on a set of records and return a single returned value. Aggregate functions ignore null value when performing calculation except COUNT function. Aggregate functions are often used with GROUP BY clause of SELECT statement. Here are aggregate functions which MySQL supports:

MySQL provides a bunch of statements to allow you to maintain database table more efficiently. Those statements enable you to analyze, optimize, check, and repair the database table. Here you will learn them all together with examples.

Analyze table statement
Basically analyze table statement allow you to update cardinality of an index column. By updating cardinality, you can retrieve the database faster by utilizing all index features of database tables.