TYPO3 Core

Here you go:

page = PAGE
page.10 = COA
page.10 {

  10 = CONTENT
  10 {
    table = tt_content
    select {            
      selectFields = tt_content.header,be_users.username
      join = be_users ON tt_content.cruser_id = be_users.uid
    }
    renderObj = COA
    renderObj {
      10 = TEXT
      10.field = header

      20 = TEXT
      20.field = username
    }  
  }
}

results in

caller
t3lib_DB::exec_SELECTquery

ERROR
Column 'uid' in field list is ambiguous

lastBuiltQuery
SELECT tt_content.header,be_users.username,uid,pid,t3ver_state FROM tt_content JOIN be_users ON tt_content.cruser_id = be_users.uid WHERE tt_content.pid IN (15) AND tt_content.deleted=0 AND tt_content.t3ver_state<=0 AND tt_content.pid!=-1 AND tt_content.hidden=0 AND tt_content.starttime<=1317397620 AND (tt_content.endtime=0 OR tt_content.endtime>1317397620) AND (tt_content.fe_group='' OR tt_content.fe_group IS NULL OR tt_content.fe_group='0' OR FIND_IN_SET('0',tt_content.fe_group) OR FIND_IN_SET('-1',tt_content.fe_group))

debug_backtrace
require#78 // include#417 // TSpagegen::renderContent#74 // tslib_cObj->cObjGet#303 // tslib_cObj->cObjGetSingle#548 // tslib_content_ContentObjectArray->render#601 // tslib_cObj->cObjGet#48 // tslib_cObj->cObjGetSingle#548 // tslib_content_Content->render#601 // tslib_cObj->exec_getQuery#101 // t3lib_DB->exec_SELECT_queryArray#7345 // t3lib_DB->exec_SELECTquery#258 // t3lib_DB->debug#191

The table can be added, yes, but I guess one may have to take care of proper possible aliasing