user: Question: Tell me the dates conducted for plaid cymru of 19%
Columns: ['Date(s) conducted', 'Polling organisation/client', 'Cons', 'Plaid Cymru', 'Lib Dem', 'Others', 'Lead']
Types: ['text', 'text', 'text', 'text', 'text', 'text', 'text']
Sample row: ['5 May 2011', 'Welsh Assembly election results, 2011', '25.0%', '19.3%', '10.6%', '2.8%', '17.3%']
SQL:

assistant: SELECT "Date(s) conducted" FROM "Table" WHERE "Plaid Cymru" = '19%';