这篇“PGSQL怎么查询最近N天的数据及SQL语句实现替换字段内容的方法”文章的知识点大部分人都不太理解，所以小编给大家总结了以下内容，内容详细，步骤清晰，具有一定的借鉴价值，希望大家阅读完这篇文章能有所收获，下面我们一起来看看这篇“PGSQL怎么查询最近N天的数据及SQL语句实现替换字段内容的方法”文章吧。
1、用SQL查询最近N天的数据
思路：先获取当前的时间，然后更具当前时间去减去对应的天数，就可以得到需要的天数了。然后用这些天数作为条件，然后即可查询出需要多少天的数据了。
-- 获取当前时间
SELECT CURRENT_TIMESTAMP;
-- 或
SELECT now();
select CURRENT_TIMESTAMP :: DATE AS "当前日期";
SELECT CURRENT_DATE;
select CURRENT_TIMESTAMP :: TIME AS "当前时间";
SELECT CURRENT_TIME;最近N天
-- 最近7天
SELECT DATE( T ) AS DAY
FROM
generate_series ( ( CURRENT_TIMESTAMP - INTERVAL '6 day' ) :: DATE,CURRENT_TIMESTAMP :: DATE, '1 days' ) AS T ;当然6 day、1 day这些也是可修改的；
--统计最近30、7、昨天、今天的数据
SELECT
count(*) AS AllData,
count(*) filter ( WHERE create_time BETWEEN ( SELECT CURRENT_DATE - INTERVAL '30 day' ) AND CURRENT_DATE ) AS Last30DayData,
count(*) filter ( WHERE create_time BETWEEN ( SELECT CURRENT_DATE - INTERVAL '7 day' ) AND CURRENT_DATE ) AS Last7DayData,
count(*) filter ( WHERE create_time BETWEEN ( SELECT CURRENT_DATE - INTERVAL '1 day' ) AND CURRENT_DATE ) AS YesterdayData,
count(*) filter ( WHERE create_time >= CURRENT_DATE ) AS todayAddData
FROM
table_name;实例如下：查询lic_plate字段不为空和为空的最近7天的数据
-- 查询lic_plate字段不为空的最近7天的数据
select count(tn.lic_plate) AS number,tn.create_time AS percentage
from table_name tn
where tn.create_time in (SELECT DATE(T) AS DAY
FROM generate_series((CURRENT_TIMESTAMP - INTERVAL '6 day') :: DATE, CURRENT_TIMESTAMP :: DATE,'1 days') AS T) AND lic_plate is not null
group by tn.create_time order by tn.create_time;
-- 查询lic_plate字段为空的最近7天的数据
select count(id) AS number,CSQV.create_time AS percentage
from (select * from table_name tn where lic_plate is null) AS CSQV where CSQV.create_time in (SELECT DATE(T) AS DAY
FROM generate_series((CURRENT_TIMESTAMP - INTERVAL '6 day') :: DATE, CURRENT_TIMESTAMP :: DATE,'1 days') AS T)
group by CSQV.create_time;2、用SQL语句实现替换字段里的内容
思路：使用替换函数替换即可
-- 替换语句
update 表名 set 替换字段名 = replace(替换字段名,'被替换内容','替换内容');实例如下：将 my_test 表的 test_content 字段内容进行替换
update my_test set test_content = replace(test_content,'1','18');
替换函数：如果没有可以创建，创建函数如下：
-- replace all occurrences in string of old_substr with new_substr
-- auto-generated definition
create function replace(text, text, text) returns text
immutable
strict
cost 1
language internal
as
$$begin
-- missing source code
end;$$;
comment on function replace(text, text, text) is 'replace all occurrences in string of old_substr with new_substr';3、SQL将查询结果赋值
--查询表数据，给test_content字段并赋值
select test_id,test_code,'测试数据' test_content from my_test;
--查询表数据给自定义 ABCD字段 并赋值
select test_id,test_code,'测试数据' ABCD from my_test;4、SQL查询字段内容为 NULL值时候赋值
select test_id,test_code,COALESCE(test_content,'测试数据') ABCD from my_test;
-- ||
select test_id,test_code,
CASE
WHEN test_content IS NOT NULL THEN test_content
ELSE '测试数据'
END ABCD from my_test;以上就是关于“PGSQL怎么查询最近N天的数据及SQL语句实现替换字段内容的方法”这篇文章的内容，相信大家都有了一定的了解，希望小编分享的内容对大家有帮助，若想了解更多相关的知识内容，请关注亿速云行业资讯频道。
