The PostgreSQL CURRENT_TIMESTAMP() function returns the current date and time with time zone, which is the time when the transaction starts.
Syntax
The following illustrates the syntax of the PostgreSQL CURRENT_TIMESTAMP() function:
1 | CURRENT_TIMESTAMP(precision) |
Arguments
The PostgreSQL CURRENT_TIMESTAMP() function accepts one optional argument.
1) precision
The precision specifies the number of digits in the fractional seconds precision in the second field of the result.
If you omit the precision argument, the CURRENT_TIMESTAMP() function will return a TIMESTAMP with a time zone that includes the full fractional seconds precision available.
Return value
The CURRENT_TIMESTAMP() function returns a TIMESTAMP WITH TIME ZONE that represents the date and time at which the transaction started.
Examples
The following example shows how to use the CURRENT_TIMESTAMP() function to get the current date and time:
1 | SELECT CURRENT_TIMESTAMP; |
The result is:
1 2 3 4 | now ------------------------------- 2017-08-15 21:05:15.723336+07 (1 row) |
Internally, the CURRENT_TIMESTAMP() is implemented with the NOW() function, therefore, the column alias is NOW.
Like the NOW() function, the CURRENT_TIMESTAMP() function can be used as the default value of a timestamp column.
Let’s take a look at the following example.
First, create a table named note that has the created_at column is a TIMESTAMP WITH TIME ZONE column.
1 2 3 4 5 | CREATE TABLE note( note_id serial PRIMARY KEY, message varchar(255) NOT NULL, created_at TIMESTAMP WITH TIME ZONE DEFAULT CURRENT_TIMESTAMP ); |
The default value of the created_at column is provided by the result of the CURRENT_TIMESTAMP() function.
Second, insert a new row into the note table:
1 2 | INSERT INTO note(message) VALUES('Testing current_timestamp function'); |
In this statement, we did not specify the value for the created_at column, therefore, it defaulted to the timestamp at which the transaction started.
Third, verify whether the insert has been taken place correctly using the following query:
1 2 3 4 | SELECT * FROM note; |
The following picture illustrates the result:
As you can see the created_at column was populated by the date and time at which the statement executed.
Remarks
In PostgreSQL, the TRANSACTION_TIMESTAMP() function is equivalent to the CURRENT_TIMESTAMP function. However, the function name TRANSACTION_TIMESTAMP clearly reflects what the function returns.
In this tutorial, you have learned how to use the PostgresQL CURRENT_TIME() to get the date and time at which the transaction starts.