WEBVTT 00:00:00.350 --> 00:00:01.331 Welcome back! 00:00:01.511 --> 00:00:03.175 Here's what we'll learn in this lesson. 00:00:03.355 --> 00:00:08.934 Give a relationship path a short name, calculate each invoice row's amount, and watch that 00:00:08.934 --> 00:00:11.227 formula respond to a quantity change. 00:00:11.407 --> 00:00:14.202 One row at a time, in our existing database. 00:00:15.600 --> 00:00:16.987 Let's call this path city. 00:00:17.167 --> 00:00:21.220 Alias column gives our two-hop customer city a reusable name. 00:00:21.400 --> 00:00:24.045 Reload the model and get a fresh table handle. 00:00:25.375 --> 00:00:27.253 Let's read and filter with that name. 00:00:27.433 --> 00:00:30.526 Dollar city follows the original relationship path. 00:00:30.706 --> 00:00:33.010 It does not store another copy of the city. 00:00:34.400 --> 00:00:36.512 Let's calculate quantity times price. 00:00:36.692 --> 00:00:39.700 Formula column declares an SQL expression. 00:00:39.880 --> 00:00:44.104 Round it to two decimal places, and describe the result as numeric. 00:00:45.434 --> 00:00:47.226 Let's read the calculated amounts. 00:00:47.406 --> 00:00:49.454 Two teas at three fifty make seven. 00:00:49.634 --> 00:00:52.685 The database evaluates the formula when we query it. 00:00:54.100 --> 00:00:56.489 Let's check whether the database needs changing. 00:00:56.669 --> 00:00:58.845 True means no migration is needed. 00:00:59.025 --> 00:01:02.225 Aliases and formulas add no physical columns. 00:01:03.600 --> 00:01:06.032 Let's temporarily change the quantity to three. 00:01:06.212 --> 00:01:09.369 The calculated amount becomes ten fifty immediately. 00:01:09.549 --> 00:01:15.139 The old total imported from CSV stays seven because it is an ordinary stored column. 00:01:16.469 --> 00:01:17.877 Let's undo that change. 00:01:18.057 --> 00:01:23.710 Rollback restores the original quantity, so the rest of our examples use the same dataset. 00:01:25.100 --> 00:01:26.593 Thanks for following along! 00:01:26.773 --> 00:01:31.040 We named a path and calculated a row amount without storing another column. 00:01:31.220 --> 00:01:36.297 Next, we will summarize related records: invoice, customer and product totals.