Understanding PostgreSQL Timestamp Data Types

Summary: in this tutorial, we will introduce you to the PostgreSQL timestamp data types including timestamp and timestamptz, and show you how to use some handy functions to handle timestamp data more effectively.

Introduction to PostgreSQL timestamp

PostgreSQL provides two temporal data types for handling timestamp, one without timezone ( timestamp) and one with timezone ( timestamptz).

The timestamp data type allows you to store both date and time. However, it does not have any time zone data. It means that when you change your database server’s time zone, the timestamp value stored in the database does not change.

The timestamptz data is the timestamp with time zone. The timestamptz is a time zone-aware date and time data type. PostgreSQL stores the timestamptz in UTC value. When you insert a value into a timestamptz column, PostgreSQL converts the timestamptz value into a UTC value and stores the UTC value in the table.

When you query timestamptz from the database, PostgreSQL converts the UTC value back to the time value of the timezone set by the database server, the user, or the current database connection.

Notice that both timestamp and timestamptz uses 8 bytes for storing the timestamp value as shown in the following query:

It’s important to note that timestamptz value is stored as a UTC value. PostgreSQL does not store any timezone data with the timestamptz value.

PostgreSQL timestamp example

Let’s take a look at an example of using the timestamp and timestamptz to have a better understanding of how the PostgresQL handles them.

First, create a table that consists of both timestamp the timestamptz columns.

Next, set the time zone of the database server to  America/Los_Angeles.

By the way, you can see the current time zone using the SHOW TIMEZONE command:

Then, insert a new row into the timstamp_demo table:

After that, query data from the timestamp and timestamptz columns.

It returns the same values as we inserted.

Finally, change the timezone of the current session to America/New_York and query data again.

The value in the timestamp column does not change, whereas the value in the timestamptz column is adjusted to the new time zone of 'America/New_York'.

It is a generally best practice to use the timestamptz data type to store the timestamp data.

PostgreSQL timestamp functions

To handle timestamp data effectively, PostgreSQL provides some handy functions as follows:

Getting the current time

To get the current timestamp you use the NOW() function as follows:

Or you can use the CURRENT_TIMESTAMP:

To get the current time without date, you use CURRENT_TIME:

Note that both CURRENT_TIMESTAMP and CURRENT_TIME return the current time with time zone.

To get the time of day in the string format, you use the timeofday() function.

Convert between timezones

To convert a timestamp to another time zone, you use the timezone(zone, timestamp) function.

The current timezone is America/Los_Angeles.

To convert 2016-06-01 00:00 to America/New_York timezone, you use the timezone() function as follows:

Note that we pass the timestamp as a string to the timezone() function, PostgreSQL casts it to timestamptz implicitly. It is better to cast a timestamp value to the timestamptz data type explicitly as the following statement:

In this tutorial, we have introduced you to the PostgreSQL timestamp data type and shown you how to use some useful functions for manipulating timestamp values.