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Everything in Details: DBMS Implementations
One book cannot possibly cover all existingdatabase implementations, and taking into consideration all these aspects,
we've decided to concentrate on "the big three": Oracle Database, IBM DB2 UDB,
and Microsoft SQL Server. These implementations have many common
characteristics: They are all industrial-strength enterprise level relational
databases (relational database model and SQL standards are covered later in
this chapter), they use Structured Command Language (SQL) standardized by the
American National Standards Institute (ANSI) and the International Organization
for Standardization (ISO), and all three are able to run on Windows operating
system. Oracle also is available on virtually any UNIX flavor, Linux, MVS, and
OpenVMS; DB2 UDB is running on UNIX/Linux, NUMA-Q, MVS, OS/2, and AS/400.
| Note | ANSI is a private, nonprofit organization that administers and coordinates the U.S. voluntary standardization and conformity assessment system. The Institute's mission is to enhance both the global competitiveness of U.S. business and the U.S. quality of life by promoting and facilitating voluntary consensus standards and conformity assessment systems, and safeguarding their integrity. ANSI was founded October 18, 1918 and is the official U.S. representative to the International Organization for Standardization (ISO) and some other international institutions. |
The problem is, none of the databases
mentioned earlier is 100 percent ANSI SQL compliant. (We'll talk about three
levels of conformance on the following pages; the feature compliance list is
given in
Appendix
J.) Each of these databases shares the basic SQL syntax (though some
diversity exists even there), but the language operators, naming restrictions,
internal functions, datatypes (especially date and time related), and
procedural language extensions are implemented differently.
| Cross-References | See Chapter 14 for more information on the SQL procedural extensions. |
Table 1-1 compares some data on maximum name
lengths supported by different database implementations.
IBM DB2 8.1 | MS SQL Server 2000 | Oracle 9i | |
|---|---|---|---|
Column name length (characters) | 30 | 128 | 30 |
Constraint name length (characters) | 18 | 128 | 30 |
Index name length (characters) | 128 | 128 | 30 |
Number of table columns | 255 | 1023 | 1000 |
In an ideal world the standards would rule
supreme, and SQL would be freely shared among different implementations for the
benefit of humanity. Unfortunately, the reality looks somewhat different. While
it is possible to distill a standard SQL understood by all database vendors'
products, anything above some very trivial tasks would be better, quicker
accomplished with implementation-specific features.
