Sams Teach Yourself SQL in 24 Hours, Second Edition

Summary

You have learned the three basic commands in Data Manipulation Language (DML): the INSERT, UPDATE, and DELETE statements. As you have seen, data manipulation is a very powerful part of SQL, allowing the database user to populate tables with new data, update existing data, and delete data.

A very important lesson when updating or deleting data from tables in a database is sometimes learned when neglecting the use of the WHERE clause. Remember that the WHERE clause places conditions on an SQL statement—particularly in the case of UDPATE and DELETE operations, when specifying specific rows of data that will be affected during a transaction. All target table data rows are affected if the WHERE clause is not used, which could be disastrous ...