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Comment by rosser | Hacker News Reader

Quibble: the "now()" function doesn't return the time of statement start; it returns the time of transaction start.

  $ psql -q
  rosser=# begin;
  rosser=# select now();
                now              
  -------------------------------
   2015-09-11 02:28:54.262142-07
  (1 row)
  
  rosser=# select now();
                now              
  -------------------------------
   2015-09-11 02:28:54.262142-07
  (1 row)

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That's also not completely acurate:

  postgres=> SELECT now(), now(), clock_timestamp(), clock_timestamp();
              now              |              now              |        clock_timestamp        |       clock_timestamp

-------------------------------+-------------------------------+-------------------------------+------------------------------

  2015-09-11 09:57:00.414422+00 | 2015-09-11 09:57:00.414422+00 | 2015-09-11 09:57:00.419087+00 | 2015-09-11 09:57:00.41909+00

Now() stays the same for the entire statement as well. clock_timestamp() doesn't.

If you ever manage to have multiple transactions in one statement please email me.

Thanks for the chuckle.

(Yes, I know this adds nothing to the discussion)

Easy. Just use dblink or foreign table to execute part of the statement inside other transaction. dblink to the same server/db is often used as way to create an "AUTONOMOUS_TRANSACTION"

Came here to mention this. Aside from now()/transaction_timestamp() and clock_timestamp() there's also statement_timestamp() that returns the start time of the current statement.

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