WEBVTT 00:00:00.290 --> 00:00:03.280 So in the last quiz, you saw one example of an aggregation, 00:00:03.280 --> 00:00:07.450 a database operation that summarises multiple rows into a single row. 00:00:07.450 --> 00:00:09.860 Counting up the number of gorillas in the animals table, 00:00:09.860 --> 00:00:11.510 was a count aggregation. 00:00:11.510 --> 00:00:15.060 It takes several rows, each representing one gorilla, and 00:00:15.060 --> 00:00:16.980 turns them into one gorilla representing the count. 00:00:18.090 --> 00:00:21.080 Any time we want to compute a single result from a set of values, 00:00:21.080 --> 00:00:22.530 that's an aggregation. 00:00:22.530 --> 00:00:26.430 Here are some of the most common aggregation functions in SQL. 00:00:26.430 --> 00:00:30.120 Count is different from the other ones, in that it takes values of any type, and 00:00:30.120 --> 00:00:30.870 returns a number. 00:00:31.920 --> 00:00:35.130 Most of the other aggregations only work on numbers. 00:00:35.130 --> 00:00:38.850 For instance, you can't the average of a column of string values, 00:00:38.850 --> 00:00:40.310 because only numbers have an average. 00:00:41.310 --> 00:00:43.880 We'll see a lot more about aggregations in the next lesson.