Mysql count case when distinct

It could be a list of those values, or the count of such unique entries, inside a dataset. In this case , MySQL uses the combination of values in these columns to determine the uniqueness of the row in the result set. Distinct count with case statement. In your case , in the expression you have case statement rite. Something went wrong on our end.

Usually I do this to set a condition, usually time based. VIPs, count(distinct case when not vip then customer else null end) as Not_VIPs from table group by city. In this case , when mysql walks over each row, it will process all counts, and no need to scanning the entire table over and over again.

First things first: If you have a huge dataset and can tolerate some imprecision, a probabilistic counter like HyperLogLog can be your best bet. One of the problems you may be faced with is that you want to get a distinct list of values from a table to show. We can count during aggregation using GROUP BY to make distinct when needed after the select statement to show the data with counts. DISTINCT operates on a single column. I have a simple test case that hits this bug in 5. After I submit this comment I will try to upload the myisam table files.

I installed the community version of 5. Count the distinct buyers each cell. If there are no matching rows, MAX() returns NULL. The above query would give you the number of distinct users that placed orders on any given day. So, if one user places two orders in a single day, that user would still only count as one item in the above query. This is very cool, but what happens when you need more information.

That’s also a bug in your query. You meant to count the number of times the column’s value is not null. This in my experience is pretty unlikely — people rarely do this.

Per month, I think I found it out. I hope that you could provide me with a solution or advice. In general whenever we have to use ‘distinct’ clause along with case statement, it always resides outside the case statement unless we are using a sub-query in the case statement. In today’s follow-up, we’ll use the COUNT() function in more sophisticated ways to tally unique values as well as those which satisfy a condition.

MSSQL and Oracle do not support it in any current versions. NOTE − All the SQL queries are case insensitive so it does not make any difference if you give ZARA or Zara in WHERE condition. Solved: I would like to count numbers of distinct cases that meet different criteria in my large dataset. This is done by using Year function on OrderDate column in the sub-query and using YR as column alias.

By using the distinct function, the sub-query gives us a unique list of CustomerIDs each year. Then the outer query aggregates the result set from the sub-query by using GROUP BY on the YR column and puts a count on the CustomerID column. So the end result is that we get a distinct count of CustomerIDs for each year.

If you want case -insensitive distinct , you need to use UPPER() or LOWER(). Generally speaking, you can use the CASE expression anywhere that allows a valid expression e. MySQL CASE expression is a control flow structure that allows you to add if-else logic to a query. The CASE expression has two forms: simple CASE and searched CASE.

SELECT, WHERE and ORDER BY clauses. Returns a count of the number of rows with different non- NULL expr values. In MySQL , you can obtain the number of distinct expression combinations that do not contain NULL by giving a list of expressions.

The SQL COUNT (), AVG() and SUM() Functions. The COUNT () function returns the number of rows that matches a specified criteria. The AVG() function returns the average value of a numeric column.

The SUM() function returns the total sum of a numeric column.