在postgresql中获取上个月的数据

Question

SELECT *
FROM Conference WHERE date_start ---don't know how to proceed---

如何检查是否date_start已在上个月？谢谢.

Answer 1

从当前月份减去一个月,然后将其"截断"到该日期的开头.由于您不希望包含"this"月份的行,因此您还需要为此添加条件

SELECT *
FROM Conference 
WHERE date_start >= date_trunc('month', current_date - interval '1' month)
  and date_start < date_trunc('month', current_date)

date_trunc('month', current_date - interval '1' month)将返回上个月date_trunc('month', current_date)的第一天,并将返回"此"月的第一天.

Answer 2

SELECT * FROM Conference WHERE date_trunc('month', date_start)=
  date_trunc('month', current_date - interval '1 month')

小心时区

date_trunc('month', (date_start at time zone 'UTC'))

另外，您可以添加索引以使其更快

CREATE OR REPLACE FUNCTION fn_my_date_trunc(period text,
 some_time timestamp with time zone) 
  RETURNS timestamp with time zone
AS
$BODY$
    select date_trunc($1, $2);
$BODY$
LANGUAGE sql
IMMUTABLE;

CREATE INDEX "IdxConferenceDateStart" ON Conference
 (fn_my_date_trunc('month', (date_start at time zone 'UTC')));

是的，当然，您必须在请求中使用声明的函数“fn_my_date_trunc”才能自动使用此索引（并将日期时间转换为时区日期时间）