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landing/docs/Introduction-To-Databases/020-TCL-commands.md

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+# `Transaction Control Language`
+
+  - `Transaction Control Language` can be defined as the portion of a database language used for `maintaining consistency` of the database and `managing transactions` in the database. 
+  
+  - A set of `SQL statements` that are `co-related logically and executed on the data stored in the table` is known as a `transaction`.
+
+## `TCL` Commands
+
+- `COMMIT` Command
+- `ROLLBACK` Command
+- `SAVEPOINT` Command
+
+## `COMMIT`
+
+The main use of `COMMIT` command is to `make the transaction permanent`. If there is a need for any transaction to be done in the database that transaction permanent through commit command. 
+
+### Syntax
+```sql
+COMMIT;
+```
+
+## `ROLLBACK`
+
+Using this command, the database can be `restored to the last committed state`. Additionally, it is also used with savepoint command for jumping to a savepoint in a transaction.
+
+### Syntax
+```sql
+ROLLBACK TO savepoint-name;
+```
+
+## `SAVEPOINT`
+
+The main use of the Savepoint command is to save a transaction temporarily. This way users can rollback to the point whenever it is needed.
+
+### Syntax
+```sql
+SAVEPOINT savepoint-name;
+```
+
+## Examples
+
+#### This is purchase table that we are going to use through this tutorial
+
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    10 | Sanskriti     |
+| Bag          |  1000 | Sanskriti     |
+| Vegetables   |   500 | Sanskriti     |
+| Shoes        |  5000 | Sanskriti     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+
+```sql
+UPDATE purchase SET price = 20 WHERE item = "Pen";
+```
+##### O/P :  Query OK, 1 row affected (3.02 sec) (Update the price of Pen set it from 10 to 20)
+
+```sql
+SELECT * FROM purchase;
+```
+##### O/P
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    20 | Sanskriti     |
+| Bag          |  1000 | Sanskriti     |
+| Vegetables   |   500 | Sanskriti     |
+| Shoes        |  5000 | Sanskriti     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+
+```sql
+START TRANSACTION;
+```
+##### Start transaction
+
+```sql
+COMMIT;
+```
+##### Saved/ Confirmed the transactions till this point 
+
+```sql
+ROLLBACK;
+```
+##### Lets consider we tried to rollback above transaction
+
+```sql
+SELECT * FROM purchase;
+```
+#### O/P:
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    20 | Sanskriti     |
+| Bag          |  1000 | Sanskriti     |
+| Vegetables   |   500 | Sanskriti     |
+| Shoes        |  5000 | Sanskriti     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+##### As we have committed the transactions the `rollback` will not affect anything
+
+```sql 
+SAVEPOINT  sv_update;
+```
+##### Create the `savepoint` the transactions above this will not be rollbacked
+
+```sql 
+UPDATE purchase SET price = 30 WHERE item = "Pen";
+```
+#### O/P : Query OK, 1 row affected (0.57 sec)
+#### Rows matched: 1  Changed: 1  Warnings: 0
+
+```sql 
+SELECT * FROM purchase;
+```
+
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    30 | Sanskriti     |
+| Bag          |  1000 | Sanskriti     |
+| Vegetables   |   500 | Sanskriti     |
+| Shoes        |  5000 | Sanskriti     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+##### price of pen is changed to 30 using the `update` command
+
+```sql
+ROLLBACK to sv_update;
+```
+##### Now if we `rollback` to the `savepoint` price should be 20 after `rollback` lets see
+
+```sql 
+SELECT * FROM purchase;
+```
+
+| item         | price | customer_name |
+|--------------|-------|---------------|
+| Pen          |    20 | Sanskriti     |
+| Bag          |  1000 | Sanskriti     |
+| Vegetables   |   500 | Sanskriti     |
+| Shoes        |  5000 | Sanskriti     |
+| Water Bottle |   800 | XYZ           |
+| Mouse        |   120 | ABC           |
+| Sun Glasses  |  1350 | ABC           |
+| Torch        |   850 | ABC           |
+##### As expected we can see `update` query is rollbacked to sv_update.
+
+
+
+## Conclusion
+
+With this short tutorial we have learnt TCL commands.