pgsql获取上一个月 上一个月第一天 上一个月最后一天

测试数据：

select

TO_CHAR((DATE_TRUNC('MONTH', CURRENT_DATE) + INTERVAL '-1 MONTH')::DATE,'YYYYMM') AS "LAST_MONTH",

TO_CHAR((DATE_TRUNC('MONTH', CURRENT_DATE) + INTERVAL '-1 MONTH')::DATE,'YYYYMMDD') AS "LASST_MONTH_FIRST_DAY",

TO_CHAR((DATE_TRUNC('MONTH', CURRENT_DATE) + INTERVAL '-1 DAY')::DATE,'YYYYMMDD') AS "LASST_MONTH_END_DAY"

select

TO_CHAR((DATE_TRUNC('MONTH',TO_DATE('0521','YYYYMMDD')) + INTERVAL '-1 MONTH')::DATE,'YYYYMM') AS "LAST_MONTH",

TO_CHAR((DATE_TRUNC('MONTH',TO_DATE('0521','YYYYMMDD')) + INTERVAL '-1 MONTH')::DATE,'YYYYMMDD') AS "LASST_MONTH_FIRST_DAY",

TO_CHAR((DATE_TRUNC('MONTH',TO_DATE('0521','YYYYMMDD')) + INTERVAL '-1 DAY')::DATE,'YYYYMMDD') AS "LASST_MONTH_END_DAY"