TIMESTAMP型のカラムから曜日を取得
select name,email,( case EXTRACT(DOW FROM date) when 0 then '日' when 1 then '月' when 2 then '火' when 3 then '水' when 4 then '木' when 5 then '金' when 6 then '土' end ) as day FROM test_table ;
http://www.sraoss.co.jp/PostgreSQL/Manual/PostgreSQL-7.1-ja/functions-datetime.html