Limiting the Number of Results

Databases can store massive amounts of data, and 0:00 often you don't want to bring back all of the results. 0:04 It's slow to do something like that, it affects the performance for 0:07 other users, and in most cases you only want a subset of rows. 0:10 Not all of them are needed. 0:14 Imagine your company, 0:16 an e-commerce site, launched nine different marketing campaigns using email, 0:17 television, banner ads, Google ads, and a variety of other marketing channels. 0:22 The marketing team wants to know which of these campaigns produced the most revenue. 0:28 They want to find out the top three effective marketing campaigns. 0:33 Fortunately your website tracks all of this information and 0:37 stores it in a database. 0:41 Let's take a look in our database to see how we can answer this question. 0:43 Let's have a look at the campaigns table. 0:47 We have an ID column, the name of the campaign and the number of sales. 0:50 Let's start with a general select staff from campaign statement. 0:56 We want to order the results by the number of sales but 1:01 in a descending order, meaning from the largest to the smallest number of sales. 1:05 Remember the marketing team only wants the top three results. 1:12 We could retrieve all the results and then manually pick off the top three or 1:16 just give the full list to the person in the marketing department, 1:20 which may be a bit distracting to whoever this report is intended for. 1:23 Luckily SQL provides a way to limit the amount of results returned. 1:28 To retrieve just a handful of the total of results, 1:33 we use the LIMIT keyword followed by the number of rows we want retrieved. 1:36 When we run this query now, we get the top three campaigns that generate sales. 1:43 To recap, you can start any query you'd like and 1:49 end it with the LIMIT keyword with the number of rows you'd like returned. 1:53 You can also use it with queries with no conditions and with any number 1:57 of conditions and including other SQL keywords like ORDER BY. 2:03 The LIMIT keyword with the number of rows you want returning 2:09 must be at the end of each query. 2:12 Putting LIMIT anywhere but at the end of the statement generates a syntax error. 2:15 You've already limited results with the WHERE clause, but 2:21 now you can limit results with the LIMIT keyword. 2:25 With WHERE clauses you need to know specifically the conditions you want to 2:29 filter by, whereas with LIMIT, 2:32 you're just concerned with the number of records returned. 2:34 LIMIT isn't available in all SQL databases. 2:38 Other databases can use a different keyword and syntax. 2:41 I will include some code examples in the teacher's notes below. 2:45