What does mul mean in mysql

This article mainly introduces what mul means in mysql. It has a certain reference value and can be used for reference by friends who need it. I hope you will learn a lot after reading this article. Next, let the editor take you to learn about it.

In mysql, mul is Key, while key means key. Key is divided into primary key primary key, foreign key FOREIGN KEY and general key. When Key is MUL, then the value of the column can be repeated, and the column is a leading column of a non-unique index.

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Key means key, and key is divided into primary key primary key, foreign key FOREIGN KEY, and general key (that is, index). This sentence actually creates an index.

It should be said that the key attribute:

1. If the Key is empty, the value of the column can be repeated, indicating that the column does not have an index or is a non-leading column of a non-unique composite index.

two。 If Key is PRI, then the column is part of the primary key.

3. If Key is UNI, then the column is the first column (leading column) of a unique value index and cannot contain null values (NULL).

4. If Key is MUL, then the value of the column can be repeated, and the column is the leading column of a non-unique index (the first column) or part of a unique index but can contain a null value of NULL.

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