Grouping Data

Grouping Data

To aggregate data, we tack the GROUP BY clause onto our SELECT statement. To do so, we must also have some aggregation methodology, most typically COUNT().

The format is simply:

SELECT field1, COUNT(*)
FROM tablename
WHERE ...
GROUP BY field [,field, field]

Examples

1. How many of each gender are in sws.people?
2. Create a query to show the number of years employed, and how many people are in that group.

Having

And then there was HAVING. It’s like WHERE, but different.

SELECT field1, COUNT(*)
FROM tablename
GROUP BY field
HAVING expression = expression

Examples

1. How many occurrences of people having the same last name?
2. How many genders have more than 100 people of that type?

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