In PostgreSQL, the now() function returns the current date and time (including the time zone offset), at the start of the current transaction.

It’s the equivalent of the transaction_timestamp() function.

It’s also similar to the current_timestamp function (when called without an argument).

The now() function doesn’t accept any parameters, so you can’t specify its precision, whereas current_timestamp can be called with or without a precision parameter.

Also, now() is non-SQL-standard (as is the transaction_timestamp() function).

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In PostgreSQL, timeofday() is a non-SQL-standard time function that returns the current date and time, with the time zone abbreviation.

It’s similar to the clock_timestamp() function, except that it returns its result as a formatted text string rather than a timestamp with time zone value. 

The result of both functions changes throughout the execution of a statement. Therefore, you could get a different result in different parts of the statement if you call the functions multiple times within a single statement.

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In PostgreSQL, the localtime function returns the local time of the day, without the time zone offset.

If you need the time zone offset, use current_time() instead.

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In PostgreSQL, the current_time function returns the current time, including the time zone offset.

The time returned is based on the start time of the current transaction.

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In PostgreSQL, the current_date function returns the current date.

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In PostgreSQL, the date_trunc() function truncates a date/time value to a specified precision.

It can also truncate the value to a specified precision in a specified time zone.

You could think of it as a date version of the trunc() function (which truncates numbers).

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In PostgreSQL, you can use the timezone() function to convert a timestamp to another timezone.

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