How to Convert Epoch Time to Date in SQL?

Introduction

The epoch is the date and time relative to which a computer's clock and timestamp values are determined. Epoch time is commonly used in computer systems to represent a point in time. It is typically represented as a single integer value, which represents the number of seconds that have elapsed since the epoch.

In SQL, you can convert an epoch time value to a date by using the to_timestamp() function. This function converts an epoch time value (which is typically stored as a BIGINT or INT data type) to a timestamp with time zone value. The resulting timestamp value can then be formatted as a date using the `to_char()` function.

Definition

In SQL, you can convert an epoch time value to a date by using the to_timestamp() function. This function converts an epoch time value (which is typically stored as a BIGINT or INT data type) to a timestamp with time zone value. The resulting timestamp value can then be formatted as a date using the to_char() function.

Syntax

Here's the basic syntax for using these functions to convert an epoch time value to a date −

SELECT to_char(to_timestamp(epoch_time), 'format') as date FROM my_table;

`epoch_time` is the column containing the epoch time values that you want to convert to dates.

`format` is a string specifying the format in which you want the date to be displayed. This string should use the following format codes −

`YYYY`: 4-digit year
`MM`: 2-digit month (01-12)
`DD`: 2-digit day of the month (01-31)
`HH24`: Hour of the day (00-23)
`MI`: Minute (00-59)
`SS`: Second (00-59)

Important Points

There are a few things to keep in mind when converting Epoch time to a date in SQL −

• Epoch time, also known as Unix time, is the number of seconds that have elapsed since January 1, 1970, at 00:00:00 UTC.

• To convert Epoch time to a date in SQL, you can use the `FROM_UNIXTIME()` function. For example, to convert the Epoch time 1577836800 to a date, you can use the following SQL query −

SELECT FROM_UNIXTIME(1577836800);

• The `FROM_UNIXTIME()` function also allows you to specify the output format of the date. For example, to convert the Epoch time 1577836800 to a date in the format "YYYY-MM-DD HH:MM:SS", you can use the following SQL query −

SELECT FROM_UNIXTIME(1577836800,'%Y-%m-%d %H:%i:%s');

• The `FROM_UNIXTIME()` function is available in several SQL databases such as MySQL, MariaDB, and Amazon Redshift. But the behavior could be different with other databases like Oracle, MS SQL, Postgres etc.

• When you work with timestamp, timezones, please be very careful in handling them, as slight mismatch in timezones may cause your timestamps to be off by an hour.

• Double check the data type of the column you are storing the converted date. Epoch time is a bigint column, ensure that you are storing the converted date in a timestamp or datetime column if it is not of bigint.

Factors

When converting Epoch time to a date in SQL, there are several factors to consider −

• Timezone −Epoch time is based on UTC, so it is important to ensure that the timezone of the date you are converting to is correct, especially if you're working with timestamps. Make sure that your SQL server is configured to use the correct timezone and that you are aware of the timezone of your data.

• Format −As mentioned before, the FROM_UNIXTIME() function allows you to specify the output format of the date. Be sure to select a format that is suitable for your use case and that is compatible with the SQL database you are using.

• Data type −When you are storing the converted date, you need to ensure that the data type of the column is compatible with the format of the date. For example, if you're storing a date in the format "YYYY-MM-DD HH:MM:SS", then the column should be of data type timestamp or datetime.

• System date and time −Your system date and time might be different than the date and time you are working with. You need to be aware of the timezone in which your system time is running and adjust accordingly.

• Data Consistency −Careful handling of timezones and date formats is essential to ensure that data is consistent across the system. A small mistake can lead to unexpected results and inconsistencies.

• Query Performance −Converting large numbers of rows of data with bigint timestamp columns to timestamp or datetime columns can be a performance-intensive operation. Be mindful of this while designing and executing your queries, and consider limiting the scope of your query as much as possible to minimize the workload on the database.

Overall, it's important to be aware of these factors and to plan accordingly when converting Epoch time to a date in SQL to ensure accurate, consistent, and efficient results.

Example 1

Here's an example of how you can use these functions to convert an epoch time value stored in a column named `epoch_time` to a date −

SELECT to_char(to_timestamp(epoch_time), 'YYYY-MM-DD HH24:MI:SS') as date FROM my_table;

This will return a column named `date` containing the date corresponding to the epoch time value stored in `epoch_time`, formatted as `YYYY-MM-DD HH24:MI:SS`.

Example 2

Here's an example of how you can use this function to convert an epoch time value stored in a column named `epoch_time` to a date −

SELECT to_timestamp(epoch_time) as date FROM my_table;

This will return a column named `date` containing the date corresponding to the epoch time value stored in `epoch_time`.

You can also specify the format in which you want the date to be displayed by using the `to_char()` function.

SELECT to_char(to_timestamp(epoch_time), 'YYYY-MM-DD HH24:MI:SS') as formatted_date FROM my_table;

This will return a column named `formatted_date` containing the date in the format `YYYY-MM-DD HH24:MI:SS`.

Keep in mind that the epoch time is the number of seconds that have elapsed since the epoch (00:00:00 UTC on January 1, 1970), so you will need to divide by the number of seconds in a day (86400) to get the number of days since the epoch.

Conclusion

• To convert epoch time to a date in SQL, you can use the `to_timestamp()` function to convert the epoch time value to a timestamp with time zone, and then use the `to_char()` function to format the timestamp as a date.

• The format of the resulting date can be specified using format codes such as `YYYY`, `MM`, `DD`, `HH24`, `MI`, and `SS`.