SQL language includes four types of command. In this tutorial I will describe them shortly.
Data Definition Language (DDL)
DDL is a set of commands for creating, deleting, renaming databases and tables.
CREATE Creates a new database or a table. ALTER Modifies the structure of a database or a table. DROP Deletes a database or a table. TRUNCATE Removes all table records, including allocated table spaces.
Data Manipulation Language (DML)
DML is a set of commands for inserting, deleting, updating and selecting data from the database.
SELECT Retrieve data from the table. INSERT Insert data into a table. UPDATE Updates the existing data with new data within a table. DELETE Deletes the records from the table. MERGE Merge statements to INSERT new records or UPDATE existing records depending on condition matches or not.
Data Control Language (DCL)
DCL is a set of commands for controlling permissions on the data (e.g. defining access rights)
GRANT Gives privileges to a user for accessing database data. REVOKE Removes the given privileges. ANALYZE Recomputes various statistics(information about index, cluster, table, etc) that RDBMS uses to plan its database queries. AUDIT Tracks the occurrence of a specific SQL statement or all SQL statements during the user sessions. COMMENT Writes comment to the data table.
Transaction Control Language (TCL)
TCL is a set of commands for controlling transactions which either completes entirely or not at all.
SAVEPOINT Defines a new save point and asks the server to remember the current state of the transaction within the current transaction. It could be later used to Rollback the new changes. COMMIT All the elements of the transaction are completed and should now be made persistent and accessible to all concurrent and subsequent transactions. ROLLBACK Cancels all changes made to data by that SQL transaction. SET TRANSACTION Changes the Isolation level of the transaction (e.g. READ COMMITTED | SERIALIZABLE)