WEBVTT 00:00:00.350 --> 00:00:01.331 Welcome back! 00:00:01.511 --> 00:00:02.685 Here's what we'll learn. 00:00:02.865 --> 00:00:05.382 Insert an invoice row, change it, and delete it. 00:00:05.562 --> 00:00:09.061 Then use commit and rollback to decide which changes remain. 00:00:09.241 --> 00:00:13.614 We use the same database in memory, with no custom Python triggers yet. 00:00:15.017 --> 00:00:17.065 Let's add two teas and commit the row. 00:00:17.245 --> 00:00:21.362 We supply the stored total ourselves: two times three fifty is seven. 00:00:21.542 --> 00:00:24.806 Insert adds the row; commit closes this transaction. 00:00:24.986 --> 00:00:29.999 Because SQLite is in memory, commit keeps data only while this connection exists. 00:00:30.179 --> 00:00:32.227 It does not create a database file. 00:00:33.617 --> 00:00:35.430 Let's change the quantity to three. 00:00:35.610 --> 00:00:40.154 Read the physical fields, copy the record and update quantity and total together. 00:00:40.334 --> 00:00:44.238 Table update does not read or merge previous values for us. 00:00:44.418 --> 00:00:48.877 Passing old record makes those previous values available to the write cycle. 00:00:49.057 --> 00:00:50.827 We leave this change uncommitted. 00:00:52.217 --> 00:00:54.371 Let's update the selection to four teas. 00:00:54.551 --> 00:01:00.013 Query update reads the selected records, merges our changes, and calls table update with 00:01:00.013 --> 00:01:01.378 their previous values. 00:01:01.558 --> 00:01:03.329 We pass only the changed fields. 00:01:03.509 --> 00:01:06.367 Its result is a list of updated primary keys. 00:01:06.547 --> 00:01:09.129 Our filter selects just row nine hundred and one. 00:01:10.517 --> 00:01:13.205 Let's delete the row, then undo our pending work. 00:01:13.385 --> 00:01:15.966 Query delete returns the removed records. 00:01:16.146 --> 00:01:18.386 The empty fetch confirms the row is gone. 00:01:18.566 --> 00:01:23.046 Rollback restores its last committed state: quantity two and total seven. 00:01:23.226 --> 00:01:27.685 It undoes both updates and the deletion together, not just the last statement. 00:01:29.017 --> 00:01:31.065 Let's clean up and commit the deletion. 00:01:31.245 --> 00:01:32.887 This time we commit the delete. 00:01:33.067 --> 00:01:35.201 The original thirty-six rows remain. 00:01:35.381 --> 00:01:40.437 The final commit closes the count query's read transaction, ready for the next lesson. 00:01:41.817 --> 00:01:43.310 Thanks for following along! 00:01:43.490 --> 00:01:49.250 We inserted, updated and deleted a row, and separated committed changes from pending work. 00:01:49.430 --> 00:01:51.798 We supplied every stored total ourselves. 00:01:51.978 --> 00:01:56.757 In the next lesson, Python triggers will calculate and validate those totals for us.