Mysql optimization techniques for querying dates based on time

For example, to query yesterday's newly registered users, there are two ways to write it:

EXPLAIN
select * from chess_user u where DATE_FORMAT(u.register_time,'%Y-%m-%d')='2018-01-25';
EXPLAIN
select * from chess_user u where u.register_time BETWEEN '2018-01-25 00:00:00' and '2018-01-25 23:59:59';

The register_time field is of datetime type. To convert it to a date and then match it, you need to query all rows for filtering. The second way of writing can use the index created on the register_time field to make the query extremely fast!

Attach date conversion function

 DECLARE yt varchar(10); #Yesterday DECLARE yt_bt varchar(19); #Yesterday's start time DECLARE yt_et varchar(19); #Yesterday's end time #Set variables SET yt=DATE_FORMAT(DATE_ADD(now(),INTERVAL -1 day),'%Y-%m-%d');
 SET yt_bt=DATE_FORMAT(DATE_ADD(now(),INTERVAL -1 day),'%Y-%m-%d 00:00:00');
 SET yt_et=DATE_FORMAT(DATE_ADD(now(),INTERVAL -1 day),'%Y-%m-%d 23:59:59');

Summarize

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