PGSQL查询最近N天的数据及SQL语句实现替换字段内容寻技术

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;