DML statements are used to work with the data in tables. When you are connected to most multi-user databases (whether in a client program or by a connection from a Web page script), you are in effect working with a private copy of your tables that can’t be seen by anyone else until you are finished (or tell the system that you are finished).

The data manipulation language statements include:

DML Type	Description
INSERT	The insert statement is used, obviously, to add new rows to a table The comma-delimited list of values must match the table structure exactly in the number of attributes and the data type of each attribute. Character type values are always enclosed in single quotes; number values are never in quotes; date values are often (but not always) in the format in the format that the database vendor defaults.
SELECT	Retrieve data from the the database
UPDATE	The update statement is used to change values that are already in a table The update expression can be a constant, any computed value, or even the result of a SELECT statement that returns a single row and a single column. If the WHERE clause is omitted, then the specified attribute is set to the same value in every row of the table (which is usually not what you want to do). You can also set multiple attribute values at the same time with a comma-delimited list of attribute=expression pairs.
DELETE	The delete statement does just that, for rows in a table If the WHERE clause is omitted, then every row of the table is deleted (which again is usually not what you want to do)—and again, you will not get a “do you really want to do this?” message.
MERGE	Performs insert, update, or delete operations on a target table based on the results of a join with a source table. For example, you can synchronize two tables by inserting, updating, or deleting rows in one table based on differences found in the other table
COMMIT	If you are using a large multi-user system, you may need to make your DML changes visible to the rest of the users of the database. Although this might be done automatically when you log out, you could also just type "commit"
ROLLBACK	If you’ve messed up your changes in this type of system, and want to restore your private copy of the database to the way it was before you started (this only works if you haven’t already typed COMMIT), just type "rollback"