TRANSACTION_TIMESTAMP
Returns a value of type TIME WITH TIMEZONE that represents the start of the current transaction.
	Returns a value of type 
`TIME WITH TIMEZONE` that represents the start of the current transaction.
The return value does not change during the transaction. Thus, multiple calls to TRANSACTION_TIMESTAMP within the same transaction return the same timestamp.
TRANSACTION_TIMESTAMP is equivalent to 
CURRENT_TIMESTAMP, except it does not accept a precision parameter.
Behavior type
StableSyntax
TRANSACTION_TIMESTAMP()
Examples
=> SELECT foo, bar FROM (SELECT TRANSACTION_TIMESTAMP() AS foo)foo, (SELECT TRANSACTION_TIMESTAMP() as bar)bar;
              foo              |              bar
-------------------------------+-------------------------------
 2016-12-12 08:18:00.988528-05 | 2016-12-12 08:18:00.988528-05
(1 row)