What does mul mean in mysql

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

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key means key, and key is divided into primary key. FOREIGN KEY, and general keys (ie indexes). This sentence actually creates an index.

It should be said that it is the key attribute:

1. If Key is empty, then the column value can be repeated, indicating that the column has no index, or is a non-unique composite index. Leading column.

2. If Key is PRI, then this 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. The column is the leading column (first column) of a non-unique index or is a component of a unique index but can contain null values. NULL.

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