PostgreSQL DBA(109) - pgAdmin(Don't do this：Don't use BETWEEN)
no zuo no die系列，来自于pg的wiki。
这一节的内容是：不要使用between。
理由是:
BETWEEN uses a closed-interval comparison: the values of both ends of the specified range are included in the result.
This is a particular problem with queries of the form
SELECT FROM blah WHERE timestampcol BETWEEN '2018-06-01' AND '2018-06-08';
This will include results where the timestamp is exactly 2018-06-08 00:00:00.000000, but not timestamps later in that same day. So the query might seem to work, but as soon as you get an entry exactly on midnight, you'll end up double-counting it.
Instead, do:
SELECT FROM blah WHERE timestampcol >= '2018-06-01' AND timestampcol < '2018-06-08'
原因是between是闭合区间，在处理日期时会丢失精度，比如日期'2018-06-08'会认为是'2018-06-08 00:00:00.000000'而不是'2018-06-08 23:59:59.999999'，下面举例说明。
创建数据表并插入数据
[local]:5432 pg12@testdb=# drop table if exists t_between;DROP TABLETime: 4.715 ms[local]:5432 pg12@testdb=# create table t_between(id int,tz timestamptz);CREATE TABLETime: 4.788 ms[local]:5432 pg12@testdb=# [local]:5432 pg12@testdb=# insert into t_between values(1,CURRENT_TIMESTAMP);INSERT 0 1Time: 3.620 ms[local]:5432 pg12@testdb=# insert into t_between values(2,now());INSERT 0 1Time: 2.319 ms[local]:5432 pg12@testdb=# insert into t_between values(3,date_trunc('second',CURRENT_TIMESTAMP));INSERT 0 1Time: 2.542 ms[local]:5432 pg12@testdb=# insert into t_between values(4,date_trunc('day',CURRENT_TIMESTAMP));INSERT 0 1Time: 2.766 ms[local]:5432 pg12@testdb=# select * from t_between order by id; id | tz ----+------------------------------- 1 | 2019-10-17 11:47:07.876236+08 2 | 2019-10-17 11:47:07.881309+08 3 | 2019-10-17 11:47:07+08 4 | 2019-10-17 00:00:00+08(4 rows)Time: 1.760 ms查询数据
[local]:5432 pg12@testdb=# select * from t_between where tz between'2019-10-16' and '2019-10-17'; id | tz ----+------------------------ 4 | 2019-10-17 00:00:00+08(1 row)Time: 1.691 ms[local]:5432 pg12@testdb=# select * from t_between where tz >= '2019-10-16' and tz < '2019-10-17'; id | tz ----+----(0 rows)Time: 1.186 ms[local]:5432 pg12@testdb=#用between会把值为2019-10-17 00:00:00+08的数据输出，因此建议使用普通的比较符（＞、＜、＝等）。
参考资料
Don't Do This
