MySQL UNIX_TIMESTAMP() Function

The `UNIX_TIMESTAMP()` function in MySQL returns the current Unix timestamp, which is the number of seconds that have elapsed since '1970-01-01 00:00:00' UTC. It can also convert a provided date expression to a Unix timestamp.

Usage

The `UNIX_TIMESTAMP()` function is used to retrieve the current timestamp or convert a date and time value into a Unix timestamp format. This is particularly useful for date comparisons and storage.

sql
UNIX_TIMESTAMP([date]);

In this syntax, `date` is an optional argument representing the date you wish to convert. It should be a valid date expression. Invalid date formats may result in a `NULL` return value or an error, depending on the SQL mode. If omitted, the function returns the current timestamp.

Examples

1. Current Unix Timestamp

sql
SELECT UNIX_TIMESTAMP();

This example returns the current Unix timestamp at the moment of execution.

2. Convert Specific Date to Unix Timestamp

sql
SELECT UNIX_TIMESTAMP('2023-10-10 10:00:00');

This query converts the specified date and time into a Unix timestamp, providing a numerical representation. Note that the function returns an integer value representing seconds, not fractional seconds.

3. Using UNIX_TIMESTAMP() in a WHERE Clause

sql
SELECT *
FROM events
WHERE event_time < FROM_UNIXTIME(UNIX_TIMESTAMP() - 86400);

In this example, the function is used to find all events that occurred more than 24 hours ago by comparing the event time with the current timestamp minus 86,400 seconds (one day). It assumes that `event_time` is stored in a format compatible with `FROM_UNIXTIME()`, such as a Unix timestamp or a convertible date-time format.

Tips and Best Practices

• Omit the argument for the current time. When you need the current timestamp, use `UNIX_TIMESTAMP()` without arguments for simplicity.
• Store timestamps for portability. Use Unix timestamps for consistent date-time storage across different systems and time zones.
• Combine with FROM_UNIXTIME(). Use `FROM_UNIXTIME()` to convert timestamps back to a readable date format when needed.
• Be mindful of time zones. Remember that Unix timestamps are in UTC. Any provided date argument is assumed to be in the current session's time zone unless otherwise specified. Adjust for local time zones as necessary.
• Error handling for invalid dates. Be aware that invalid date expressions may return `NULL` or an error, and handle these cases appropriately.
• Human readability. While Unix timestamps are efficient for storage, they are less human-readable. Consider logging or storing the original date-time for reference if necessary for debugging.