concept entry sql rollback #5168

content/sql/concepts/commands/terms/rollback/rollback.md

@@ -0,0 +1,133 @@
+---
+Title: 'ROLLBACK'
+Description: 'Undoes any work performed in the current transaction. It can also be used to undo work performed by in-doubt transactions.'
+Subjects:
+  - 'Data Science'
+Tags:
+  - 'Database'
+  - 'Documentation'
+  - 'Functions'
+  - 'Queries'
+CatalogContent:
+  - 'learn-sql'
+  - 'paths/analyze-data-with-sql'
+---
+
+In SQL, the **`ROLLBACK`** command undoes work performed in the current transaction to a savepoint or to the last commit to the database. A SQL transaction is a series of one or more SQL statements in the current session.
+
+Therefore, the rollback procedure allows a user to undo the work to a previous point without applying these statements to the database.
+
+> Note: To learn more about how to start and commit a transaction, check out the [MySQL documentation](https://dev.mysql.com/doc/refman/8.4/en/commit.html).
+
+## Syntax
+
+```pseudo
+ROLLBACK [WORK] [TO SAVEPOINT savepoint_name];
+```
+
+- `TO SAVEPOINT savepoint_name`: Resets the database to an established savepoint `savepoint_name` within the current transaction. These savepoint names can be created using the command `SAVEPOINT savepoint_name`.
+
+### Rollback Current Transaction
+
+The following syntax can be used to undo any changes in the current transaction:
+
+```pseudo
+ROLLBACK;
+-- Or, for compatibility with some SQL standards:
+ROLLBACK WORK;
+```
+
+### Rollback Current Transaction to Savepoint
+
+To rollback to a specific savepoint, the following syntax can be used:
+
+```pseudo
+ROLLBACK [WORK] TO SAVEPOINT savepoint_name;
+```
+
+> Note: Certain statements cannot be rolled back once performed, such as creating, dropping, or altering tables and databases. For more info, check out the [MySQL documentation](https://dev.mysql.com/doc/refman/8.4/en/cannot-roll-back.html).
+
+## Example
+
+Here is a table `table_1` containing the following data:
+
+| id  | dob        | name             |
+| --- | ---------- | ---------------- |
+| 1   | 11/16/2001 | Jolly Old Chap   |
+| 2   | 1/12/2000  | Jolly Young Chap |
+
+Next, the following code is used to fix Young Chap's birthday and make him younger than Old Chap:
+
+```sql
+UPDATE table_1
+SET dob = "1/21/2024";
+SELECT * FROM table_1;
+```
+
+This gives the following as the output:
+
+| id  | dob       | name             |
+| --- | --------- | ---------------- |
+| 1   | 1/21/2024 | Jolly Old Chap   |
+| 2   | 1/21/2024 | Jolly Young Chap |
+
+However, the above output suggests that everyone's birthday has been accidentally set to `1/21/2024`.
+
+To fix that, the following code is used to rollback the transaction and update the birthday correctly:
+
+```sql
+ROLLBACK;
+UPDATE table_1
+SET dob = "1/21/2024"
+WHERE id = 2;
+SELECT * FROM table_1;
+```
+
+This gives the following as the output:
+
+| id  | dob        | name             |
+| --- | ---------- | ---------------- |
+| 1   | 11/16/2001 | Jolly Old Chap   |
+| 2   | 1/21/2024  | Jolly Young Chap |
+
+Finally, the following code adds another chap to the database and then rolls back the addition:
+
+```sql
+-- Create a savepoint, in case another error is made
+SAVEPOINT first;
+
+-- Add a new chap
+INSERT INTO table_1 (name,dob)
+  VALUES ("Jolly Medium Chap","3/22/2012");
+SELECT name FROM table_1 WHERE id=3;
+
+-- Gives "Jolly Medium Chap"
+
+-- Create a new savepoint
+SAVEPOINT second;
+
+-- Change the name
+UPDATE table_1
+  SET name = "Jolly Rancher"
+  WHERE id=3;
+SELECT name FROM table_1 WHERE id=3;
+
+-- Gives "Jolly Rancher"
+
+-- The original name feels better. So, let's go ahead and rollback.
+ROLLBACK TO SAVEPOINT second;
+SELECT name FROM table_1 WHERE id=3;
+
+-- Gives "Jolly Medium Chap"
+
+-- There is no need of the new chap anymore. Let's just go back to the save with just two chaps.
+ROLLBACK TO SAVEPOINT first;
+SELECT * FROM table_1;
+```
+
+This would output the following table:
+
+| id  | dob        | name             |
+| --- | ---------- | ---------------- |
+| 1   | 11/16/2001 | Jolly Old Chap   |
+| 2   | 1/21/2024  | Jolly Young Chap |