Find out all employees ' current (to_date= ' 9999-01-01 ') specific salary salary situation, show only once for the same salary, and display in reverse order

Topic address
Topic Description

Find out all employees ' current (to_date= ' 9999-01-01 ') specific salary salary situation, show only once for the same salary, and display in reverse order

CREATE TABLE ' salaries ' (
' emp_no ' int (one) not null,
' salary ' int (one) not null,
' from_date ' date not null,
 
   ' to_date ' date not NULL,
PRIMARY KEY (' emp_no ', ' from_date '));
 

Solution 1

Select distinct salary from 
salaries 
where to_date= ' 9999-01-01 ' ORDER by 
salary desc;

Solution 2

Select salary from 
salaries  
where to_date= ' 9999-01-01 ' GROUP by salary order by salary 
desc;

Attention

For Distinct,groupby performance. When the volume of data is very large, such as 300W of duplicate data in 10 million, the efficiency of the distinct is slightly better than group by; For a relatively small amount of data, such as 10 million of 10,000, the performance of the groupby is much better than the distnct.

MySQL get current time: Now ()

Select distinct salary from 
salaries 
where To_date>=now () Order by 
salary desc;