Menu
I have the following table structured like this:
So basically as you can see, the department goes through name changes every couple of years. Look at number 16 for example. I want a select query that will only get the name when the date is the greatest. How do I do that?
448
The SQL SELECT DISTINCT Statement The SELECT DISTINCT statement is used to return only distinct (different) values. Inside a table, a column often contains many duplicate values; and sometimes you only want to list the different (distinct) values.
As a general rule, SELECT DISTINCT incurs a fair amount of overhead for the query. Hence, you should avoid it or use it sparingly. The idea of generating duplicate rows using JOIN just to remove them with SELECT DISTINCT is rather reminiscent of Sisyphus pushing a rock up a hill, only to have it roll back down again.
GROUP BY is required if you're aggregating data, but in many cases, DISTINCT is simpler to write and read if you aren't aggregating data.
Yes, the application needs to compare every record to the "distinct" records cache as it goes. You can improve performance by using an index, particularly on the numeric and date fields.
select ID, Name from departments o
where o.thedate=
(select max(i.thedate) from departments i where o.id=i.id)
SELECT ID,
First(Name) AS FirstOfName, First(DateChange) AS FirstOfDateChange
FROM departments
GROUP BY ID
ORDER BY First(DateChange) DESC;
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
