MySQL 中的 `unsigned` 是什么意思以及何时使用它？

Question

“无符号”在 MySQL 中是什么意思，我应该什么时候使用它？

Answer 1

MySQL says:

All integer types can have an optional (nonstandard) attribute UNSIGNED. Unsigned type can be used to permit only nonnegative numbers in a column or when you need a larger upper numeric range for the column. For example, if an INT column is UNSIGNED, the size of the column's range is the same but its endpoints shift from -2147483648 and 2147483647 up to 0 and 4294967295.

When do I use it ?

Ask yourself this question: Will this field ever contain a negative value ?
If the answer is no, then you want an UNSIGNED data type.

A common mistake is to use a primary key that is an auto-increment INT starting at zero , yet the type is SIGNED , in that case you'll never touch any of the negative numbers and you are reducing the range of possible id's to half.