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SQL Overview


SQL stands for Structured Query Language. SQL is a computer language for accessing databases. It is used to store, manipulate and retrieve the data stored in a database.

SQL Commands:

SQL Commands are the instructions which are used to interact with the database to perform a specific task.

SQL Commands categories:

1. DDL (Data Definition Language):

DDL commands are used to define the structure of database objects.

1. CREATE – It is used to create database objects like table, view etc.

2. ALTER – It is used to alter the structure of the existing database object.

3. DROP – It is used to delete the existing objects from the database.

4. TRUNCATE – It remove all records from a table, including all spaces allocated for the records will be removed.

5. RENAME – It is used to rename an existing database object.

2. DML (Data Manipulation Language):

1. SELECT – It is used to retrieve the records from the database.

2. INSERT – It is used to create a record.

3. UPDATE – It is used to modify an existing record.

4. DELETE – It is used to delete all records from a table, the space for the records remain.

5. MERGE- It is used to insert or update a record.

6. CALL – call a PL/SQL or Java subprogram.

7. LOCK TABLE – It is used to control concurrency.

3. DCL (Data Control Language):

1. GRANT – It gives privileges to user.

2. REVOKE – It withdraw access privileges from a user given with the GRANT command.

4. TCL (Transaction Control):

1. COMMIT – It is used to save the work done.

2. SAVEPOINT – It is used to identify a point in a transaction to which you can roll back later.

3. ROLLBACK – It is used to restore the database to original since the last COMMIT.
 

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