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landing/docs/SQL-101/020-TCL-commands.md

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+# SQL Transaction Control
+
+Transaction Control Language (TCL) manages transactions within a database, ensuring data consistency and reliability. A transaction is a logical unit of work comprising  one or more SQL statements, executed co-relationally against data.
+
+## TCL Commands
+
+-   `COMMIT`
+-   `ROLLBACK`
+-   `SAVEPOINT`
+
+## COMMIT
+
+The `COMMIT` command final izes a transaction. All data modifications made within the transaction become permanent and visible to other database sessions. Executing `COMMIT` guarantees data persistence up to that point.
+
+### Syntax
+
+```sql
+COMMIT;
+```
+
+## ROLLBACK
+
+`ROLLBACK` discards all changes made since the transaction started or since the last `SAVEPOINT`. It restores the database to a previous state, effectively undoing operations within the transaction. This is crucial for error handling and partial transaction reversal.
+
+### Syntax
+
+```sql
+ROLLBACK TO savepoint-name;
+```
+*Note: Without the `TO savepoint-name` clause, `ROLLBACK` undoes the entire current transaction.*
+
+## SAVEPOINT
+
+A `SAVEPOINT` establishes  a marker within a transaction. You can `ROLLBACK` to a specific savepoint, partially undoing changes while retaining prior modifications within the same transaction. This allows fine-grained control over transaction scope.
+
+### Syntax
+
+```sql
+SAVE POINT savepoint-name;
+```
+
+## Examples
+
+Using the `purchase` table to demonstrate TCL command behavior.
+
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    10 |  Troy     |
+| Bag          |  1000 | Troy     |
+| Vegetables   |   500 | Troy     |
+| Shoes        |  5000 | Troy     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+
+Update the price of "Pen" from  10 to 20.
+
+```sql
+UPDATE purchase SET price = 20 WHERE item = "Pen";
+```
+
+Output indicates success. The change is applied (though not necessarily permanent yet depending on database settings). ```
+Query OK, 1 row affected (...)
+```
+
+View the updated table state.
+
+```sql
+SELECT * FROM purchase;
+```
+
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    20 | Troy     |
+| Bag          |  1000 | Troy     |
+| Vegetables   |   500 | Troy     |
+| Shoes        |  5 000 | Troy     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC            |
+
+Begin a transaction explicitly (some databases default to autocommit).
+
+```sql
+START TRANSACTION;
+```
+
+Commit the changes made so far within this explicit or implicit transaction. This makes the "Pen" price update (10 to 20)  permanent.
+
+```sql
+COMMIT;
+```
+
+Attempting to rollback now has no effect on the committed transaction.
+
+```sql
+ROLLBACK;
+```
+
+Querying the table shows the committed change persists.
+
+```sql
+SELECT  * FROM purchase;
+```
+
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    20 | Troy     |
+| Bag          |  1000  | Troy     |
+| Vegetables   |   500 | Troy     |
+| Shoes        |  5000 | Troy     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+
+Create a savepoint named `sv_update` in the current transaction. Changes before this point are protected from  rollbacks targeting this savepoint.
+
+```sql
+SAVEPOINT  sv_update;
+```
+
+Update the price of "Pen" again, from 20 to 30. This change occurs after the `sv_update` savepoint .
+
+```sql
+UPDATE purchase SET price = 30 WHERE item = "Pen";
+```
+
+Output indicates success.
+```
+Query OK, 1 row affected (...)
+```
+
+View the table state showing the new price  (30).
+
+```sql
+SELECT * FROM purchase;
+```
+
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    30 | Troy     |
+|  Bag          |  1000 | Troy     |
+| Vegetables   |   500 | Troy     |
+| Shoes        |  5000 | Troy     |
+| Water Bottle |    800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+
+Rollback the transaction specifically to the `sv_update` savepoint.  This undoes the price change from 20 to 30, but *not* the prior change from 10 to 20 because it was committed.
+
+```sql
+ROLLBACK to sv_update;
+```
+
+Querying  the table shows the state after the partial rollback. The price of "Pen" is restored to 20, as this was the state at the `sv_update` savepoint.
+
+```sql
+SELECT * FROM purchase;
+```
+
+| item          | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    20 | Troy     |
+| Bag          |  1000 | Troy     |
+| Vegetables   |    500 | Troy     |
+| Shoes        |  5000 | Troy     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC            |
+| Sun Glasses  |  1350 | ABC           |