Join Bill Weinman for an in-depth discussion in this video Aggregate functions, part of MySQL Essential Training (2014).
…Aggregate functions are functions that operate on a…set of rows rather than row by row.…For example, we'll be using the world database.…And we'll start with a simple example of an…aggregate function that we're all familiar with the Count function.…So, I'll select COUNT with an asterisk in the parenthesis.…FROM the country table.…And when I press go, you see there are 239 rows in the country table.…So this returns one result for a number of rows.…
There's 239 rows but there's only one result for the count.…The asterisk is a special case for the count…function that will count all the rows in a table.…If instead, you specify a column.…COUNT will count all the non-null values in that column.…So if I put in here population, which I know has a view null values…in it, you notice we get a smaller value; instead of 239 we get 232.…And those are the non-null values in the population column.…
The GROUP BY clause, I'll put an asterisk back in over here and we'll…specify a group by may be used to group rows for use with aggregate functions.…
- Writing queries
- Creating and updating databases and tables
- Using MySQL built-in functions
- Sorting and filtering data
- Updating tables with triggers
- Working with subselects and views
- Creating and using a stored function
Skill Level Beginner
1. Installing and Configuring the Test Environment
2. Basic Syntax
3. Creating a Database
4. MySQL Data Types
5. MySQL Functions
8. Subselects and Views
9. Stored Routines
10. PHP's PDO Interface with MySQL
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