MySQL Cookbook

Using TIMESTAMP Values

Problem

You want a record’s creation time or last modification time to be automatically recorded.

Solution

The TIMESTAMP column type can be used for this. However, it has properties that sometimes surprise people, so read this section to make sure you know what you’ll be getting. Then read the next few sections for some applications of TIMESTAMP columns.

Discussion

MySQL supports a TIMESTAMP column type that in many ways can be treated the same way as the DATETIME type. However, the TIMESTAMP type has some special properties:

• The first TIMESTAMP column in a table is special at record-creation time: its default value is the current date and time. This means you need not specify its value at all in an INSERT statement if you want the column set to the record’s creation time; MySQL will initialize it automatically. This also occurs if you set the column to NULL when creating the record.

• The first TIMESTAMP is also special whenever any columns in a row are changed from their current values. MySQL automatically updates its value to the date and time at which the change was made. Note that the update happens only if you actually change a column value. Setting a column to its current value doesn’t update the TIMESTAMP.

• Other TIMESTAMP columns in a table are not special in the same way as the first one. Their default value is zero, not the current date and time. Also, their value does not change automatically when you modify other columns; to update them, you must change ...