Typo3, Typoscript. Output timestamp of last published workspace - typo3

Question

I set up a TYPO3 6.2 with workspaces. All the content is changed in a staging workspace and published all together.
Now I want a label like "last changes: " on every page.
I don't want the date the page was changed, but the date the workspace edits were last published.
I got something like:
30 = CONTENT
30 {
table = sys_log
select {
selectFields = tstamp
where = (workspace = 1 AND tablename = 'tt_content' AND details_nr = 30 AND details = 'Published')
orderBy = tstamp DESC
max = 1
}
renderObj {
10 = TEXT
10.stdWrap.field = tstamp
10.stdWrap.wrap = (|)
}
wrap = <span class="tstamp">|</span>
}
I'm pretty much stuck here. There is no content rendered in frontend. I get the span, but the parentheses and their content is missing.
I tried to find examples, because the documentation is not that newbe-friendly written.
Thanks in advance.

Answer 1

The value you're looking for is stored in every workspace-aware table in the field t3ver_tstamp as unix timestamp. This field is updated only if data is published or "swapped", which is a special publish process.
Unfortunately the approach which selecting from the sys_log table won't work, since the relevant payload is PHP-serialized in the field log_data like e.g. a:2:{i:0;s:4:"Test";i:1;s:7:"pages:1";} (pointing to table pages with uid 1 in this example).
As far as I understood it, you want to retrieve the last point in time any record on a particular page has been published from a draft workspace to the live workspace - which means to select the maximum unix timestamp on any record for any table pointing to that particular page. Unfortunately this does not work with plain TypoScript, thus you have to implement a service implemented in PHP.
Given that you want to show the last publishing date for page with ID 123 that would require the following tasks:
SELECT t3ver_tstamp FROM pages WHERE uid=123...
foreach (array_keys($GLOBALS['TCA']) as $tableName)
SELECT MAX(t3ver_tstamp) FROM $tableName WHERE pid=123 AND t3ver_wsid=0...
determine maximum timestamp in PHP from the above