Make a summary of this including tools and what they are used for: "You use the ALTER TABLE statement to add or remove columns from a table, to modify the data type of columns, to add or remove keys, and to add or remove constraints. The syntax of the ALTER TABLE statement is shown here. You start with ALTER TABLE followed by the name of the table that you want to alter. Differently to the CREATE TABLE statement though, you do not use parentheses to enclose the parameters for the ALTER TABLE statement. Each row in the ALTER TABLE statement specifies one change that you want to make to the table. For example, to add a telephone number column to the AUTHOR table in the Library database to store the author’s telephone number, use the following statement: ALTER TABLE author ADD COLUMN telephone_number BIGINT; In this example, the data type for the column is BIGINT which can hold a number up to 19 digits long. You also use the ALTER TABLE statement to modify the data type of a column. To do this, use the ALTER COLUMN clause specifying the new data type for the column. For example, using a numeric data type for telephone number means that you cannot include parentheses, plus signs, or dashes as part of the number. You can change the column to use the CHAR data type to overcome this. This code shows how to alter the author table: ALTER TABLE author ALTER COLUMN telephone_number SET DATA TYPE CHAR(20 ); Altering the data type of a column containing existing data can cause problems though if the existing data is not compatible with the new data type. For example, changing a column from the CHAR data type to a numeric data type will not work if the column already contains non-numeric data. If you try to do this, you will see an error message in the notification log and the statement will not run. If your spec changes and you no longer need this extra column, you can again use the ALTER TABLE statement, this time with the DROP COLUMN clause, to remove the column as shown: ALTER TABLE author DROP COLUMN telephone_number; Similar to using DROP COLUMN to delete a column from a table, you use the DROP TABLE statement to delete a table from a database. If you delete a table that contains data, by default the data will be deleted alongside the table. The syntax for the DROP TABLE statement is: DROP TABLE table_name ; So, you use this statement: DROP TABLE author; to remove the table from the database. Sometimes you might want to just delete the data in a table rather than deleting the table itself. While you can use the DELETE statement without a WHERE clause to do this, it is generally quicker and more efficient to truncate the table instead. You use the TRUNCATE TABLE statement to delete all of the rows in a table. The syntax of the statement is: TRUNCATE TABLE table_name IMMEDIATE; The IMMEDIATE specifies to process the statement immediately and that it cannot be undone. So, to truncate the author table, you use this statement: TRUNCATE TABLE author IMMEDIATE; In this video, you learned that: The ALTER TABLE statement changes the structure of an existing table, for example, to add, modify, or drop columns. The DROP TABLE statement deletes an existing table. The TRUNCATE TABLE statement deletes all rows of data in a table."