Informix Guide to SQL: Tutorial
Chapter 4: Modifying Data

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Modifying data is fundamentally different from querying data. Querying data involves examining the contents of tables. Modifying data involves changing the contents of tables.

Think about what happens if the system hardware or software fails during a query. In this case, the effect on the application can be severe, but the database itself is unharmed. However, if the system fails while a modification is under way, the state of the database is in doubt. Obviously, a database in an uncertain state has far-reaching implications. Before you delete, insert, or update rows in a database, ask yourself the following questions:

Is user access to the database and its tables secure; that is, are specific users given limited database and table-level privileges?
Does the modified data preserve the existing integrity of the database?
Are systems in place that make the database relatively immune to external events that might cause system or hardware failures?

If you cannot answer yes to each of these questions, do not panic. Solutions to all these problems are built into the Informix database servers. After an introduction to the statements that modify data, this chapter discusses these solutions. Chapters 8 through 10 cover these topics in greater detail.

Informix Guide to SQL: Tutorial, version 9.1
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