0:00:00.290,0:00:03.280 So in the last quiz,[br]you saw one example of an aggregation, 0:00:03.280,0:00:07.450 a database operation that summarises[br]multiple rows into a single row. 0:00:07.450,0:00:09.860 Counting up the number of[br]gorillas in the animals table, 0:00:09.860,0:00:11.510 was a count aggregation. 0:00:11.510,0:00:15.060 It takes several rows,[br]each representing one gorilla, and 0:00:15.060,0:00:16.980 turns them into one gorilla[br]representing the count. 0:00:18.090,0:00:21.080 Any time we want to compute a single[br]result from a set of values, 0:00:21.080,0:00:22.530 that's an aggregation. 0:00:22.530,0:00:26.430 Here are some of the most common[br]aggregation functions in SQL. 0:00:26.430,0:00:30.120 Count is different from the other ones,[br]in that it takes values of any type, and 0:00:30.120,0:00:30.870 returns a number. 0:00:31.920,0:00:35.130 Most of the other aggregations[br]only work on numbers. 0:00:35.130,0:00:38.850 For instance, you can't the average[br]of a column of string values, 0:00:38.850,0:00:40.310 because only numbers have an average. 0:00:41.310,0:00:43.880 We'll see a lot more about[br]aggregations in the next lesson.