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USE GROUP BY to COUNT the number of rows for each unique entry in a given column

Let's say you want to generate counts or subtotals for a given value in a column. Given this table, "Westerosians": NameGreatHouseAllegienceAryaStarkCerceiLannisterMyrcellaLannisterYaraGreyjoyCatelynStarkSansaStark Without GROUP BY, COUNT will simply return a total number of rows: SELE...

SQL • GROUP BY

Filter GROUP BY results using a HAVING clause

A HAVING clause filters the results of a GROUP BY expression. Note: The following examples are using the Library example database. Examples: Return all authors that wrote more than one book (live example). SELECT a.Id, a.Name, COUNT(*) BooksWritten FROM BooksAuthors ba INNER JOIN Aut...

SQL • GROUP BY

Basic GROUP BY example

It might be easier if you think of GROUP BY as "for each" for the sake of explanation. The query below: SELECT EmpID, SUM (MonthlySalary) FROM Employee GROUP BY EmpID is saying: "Give me the sum of MonthlySalary's for each EmpID" So if your table looked like this: +----...

SQL • GROUP BY

ROLAP aggregation (Data Mining)

Description The SQL standard provides two additional aggregate operators. These use the polymorphic value "ALL" to denote the set of all values that an attribute can take. The two operators are: with data cube that it provides all possible combinations than the argument attributes o...

SQL • GROUP BY