Postgresql count distinct case when

DISTINCT COUNT in SELECT CASE SQL - Stack. The following statement illustrates various ways of using the COUNT () function. Hi, This works for me but the result is not that what is expected.

In this case , the combination of values in both column_and column_columns will be used for evaluating the duplicate. After executing a select statement the resultant table returns all rows according to the provided expression. The query returns the unique combination of bcolor and fcolor from the ttable. I am new topsql and am interested in counting the number of unique first time users per day.

Historically the expression ought to have been defined as count (). When both are specifie start rows are skipped before starting to count the count rows to be returned. If the count expression evaluates to NULL, it is treated as LIMIT ALL, i. The CASE first evaluates the expression and then compares the result with each value( value_ value_ …) in the WHEN clauses sequentially until it finds the match. Once the result of the expression equal to a value in a WHEN clause, the CASE returns the corresponding result in the THEN clause.

The only requirement is that we ORDER BY the field we group by (department in this case). It also allows for “grouping” by more than one field which only makes this clause even more powerful. Stack Exchange network consists of 1QA communities including Stack Overflow, the largest, most trusted online community for developers to learn, share their knowledge, and build their careers.

PostgreSQL does all the heavy lifting for us. It retrieves the number of rows that satisfy specified criteria stated within the query. Let’s look at the following statements: COUNT(column) The COUNT(column) command will return the number of columns that match the query in the SELECT statement. RE: counting distinct rows on more than one column.

In such a case , reading, reproducing, printing or further dissemination of this e-mail is strictly prohibited and may be unlawful. SQL Server gives you the ability to store mixed case data in your databases, but depending on how you create your databases SQL Server will ignore the case when you issue T-SQL commands. 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.

SQL COUNT ( ) with All In the following, we have discussed the usage of ALL clause with SQL COUNT () function to count only the non NULL value for the specified column within the argument. HLL is a great way to horizontally scale distinct count estimates in a distributed database. Count distinct or HyperLogLog. Further, certain use cases you may not be able to get by with close enough counts–you may have to be perfectly accurate. For this case count distinct in a distributed fashion will still be faster than a single node for very large datasets.

But, if you can get by with close counts HyperLogLog is your friend. I want to count the distinct users based on a rolling range of days. For example, if they have an event logged in the table within the last days of any particular date then they would be counted as an active user. NOT NULL, ip_address inet, offence text, count. Determining different data in tables.

USING (foo,bar,baz) is just a macro for: t1. The task because slightly more verbose and daunting when joining a table,. So, couple of days ago, some guy, from Periscope company wrote a blogpost about getting number of distinct elements, per group, faster using subqueries.

But when you are using CASE in pair with a where clause, you need not to follow this (more on this later). The data-type of the has to be uniform. You cannot return a string in result_and an integer in result_and so on. In postgres, distinct aggregates are a blind spot in the planner. But the distinct aggregates are not really seen by the planner, and they are always implemented with a sort.

So this is a peculiar case for postgres. A variant of this patch appears to have been applied in D6. You can use the count () function in a select statement with distinct on multiple columns to count the distinct rows.