Counting Groups of Rows

We're now going to use the Count Function to count groups of rows that have 0:00 things in common. 0:04 For example, how many products of an each category. 0:05 Well, we could start out with a query where we select the category and 0:09 oder it by the category. 0:13 We could count all of these up manually and 0:16 keep track of a tally of each category. 0:19 But there is no need for that. 0:21 I've shown you how to use the Count function to count all the rows in a table. 0:23 I've also shown you how to use Count to count the results from a query. 0:28 But for this example, we need to count the groups of rows by their category. 0:32 For example, all of the clothing products, all of the electronics products and so on. 0:38 We can do that by using the group by keywords. 0:44 At first glance, this looks like the key word distinct. 0:50 But there's a key difference. 0:53 Distinct discards any duplicates. 0:56 Where as group by, groups rows together so you can use functions like count. 0:58 Let's update this query to include the product counts. 1:04 Now, that shows us how many products are in each category. 1:12 Let's recap what we've just learned. 1:16 Let's start with keywords. 1:19 DISTINCT is used to get the unique values in a column. 1:22 Its used in the select portion of a query. 1:26 This will use the full table as a source of data to obtain distinct values. 1:29 You can narrow down the dates and get a distinct values from that. 1:35 You can use a WHERE cause. 1:39 The next sets of key words you have learned were GROUP BY, 1:42 GROUP BY appears at the end of the statement. 1:46 This allows you to run functions like counts 1:49 on collections of rows grouped by a particular value in a column. 1:52 Then you can use the function like COUNT to count all rows that are in each group. 1:57 [SOUND] Finally, you've seen COUNT counting all rows and the subsets of rows. 2:02 You've seen me build up my queries, starting with simple queries first, 2:09 then progressively getting more complex. 2:13 This is a technique you can use. 2:16 You don't have to write out your whole query in one go. 2:17