What is the unsigned constraint keyword in mysql

Unsigned constraints in MySQL restrict columns to only store non-negative values, thus preventing negative values ​​from being inserted. The specific application steps are as follows: When creating a table, use the UNSIGNED keyword to apply constraints: CREATE TABLE table_name (column_name UNSIGNED [type]); The advantages include preventing negative value insertion, improving storage efficiency, and supporting certain mathematical functions; the disadvantage is that it limits the stored values range, trying to insert a negative value will throw an error.

Unsigned constraint keywords in MySQL

In MySQL, unsigned constraints are used to limit columns to only Can store non-negative values. This can be used to ensure that the values ​​stored in the column are always positive or zero, thus preventing negative values ​​from being accidentally inserted into it.

Keywords:

• ##UNSIGNED

Use:

When creating a table, you can apply unsigned constraints to columns by specifying the UNSIGNED keyword:

<code>CREATE TABLE table_name (
  column_name UNSIGNED [type]
);</code>

For example, to create a column named age that can only store positive numbers or Zero, you can do the following:

<code>CREATE TABLE people (
  age UNSIGNED INT
);</code>

Advantages:

Prevents negative values ​​from being accidentally inserted into the column.
• Improve the storage efficiency of numeric columns because MySQL can use smaller data types to store non-negative values.
• Allows the use of certain mathematical functions and operators, such as SQUARE ROOT and MOD, which require non-negative input.

Disadvantages:

Limits the range of values ​​that can be stored in the column.
• If you try to insert a negative value into a column with an unsigned constraint, an error will be thrown.

Note:

Unsigned constraints do not apply to the FLOAT, DOUBLE, and DECIMAL data types because these types allow negative values.
• Unsigned constraints apply to integral data types such as TINYINT, SMALLINT, INT, and BIGINT.

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