In SQL Server, the timestamp data type is used to track changes made to a row in a table. It does not store any date or time information and is not related to the actual time of the system. Instead, it is a binary value that gets updated automatically whenever a row is modified.
Usage of Timestamp Data Type
The timestamp data type in SQL Server is commonly used for optimistic concurrency control. It helps in detecting whether a row has been updated since it was last read by comparing the current timestamp value with the one stored when the row was initially retrieved.
Here’s an example to illustrate its usage:
CREATE TABLE MyTable ( ID INT, Name VARCHAR(50), LastUpdated TIMESTAMP )
Whenever a modification is made to a row in this table, the LastUpdated field will automatically be updated with a new timestamp value.
Important Points about Timestamp Data Type
- 1. Implicit Updating: The timestamp column is updated implicitly by SQL Server and does not require any explicit update statement.
Uniqueness: Each row within a table will have a unique timestamp value, ensuring no two rows have the same timestamp.
- 3. Non-Nullable: The timestamp column cannot be set to NULL.
- 4. Binary Data Type: The timestamp data type is stored as binary(8) internally.
Differences between Timestamp and Datetime Data Types
The timestamp data type should not be confused with the datetime data type in SQL Server. While both involve time-related information, they serve different purposes:
- 1. Storage: The timestamp data type only requires 8 bytes of storage, while datetime requires 8 bytes for storage plus additional space for fractional seconds. Range: The timestamp data type has a range of January 1, 1753, through December 31, 9999, while datetime has a range of January 1, 1753, through December 31, 9999.
The timestamp data type in SQL Server is a useful tool for tracking changes made to rows within a table. It allows for optimistic concurrency control and automatic updating of the timestamp value whenever a modification occurs. Understanding the differences between the timestamp and datetime data types is important to utilize them effectively in database design and development.