Why does no database fully support ANSI or ISO SQL standards?
If I were designing a oil refinery, I wouldn't expect that materials from different vendors would not comply with published standards in subtle yet important ways. Pipework, valves and other components from one supplier would come with flanges and wall thicknesses to ANSI standards, as would the same parts from any other supplier. Interoperability and system safety is therefore assured.
Why then are the common databases so choosy about which parts of the standards they adhere to, and why have no 100% standards-compliant systems come to the fore? Are the standards 'broken', lacking in scope or too difficult to design for?
Taking this to conclusion; what is the point of ANSI (or ISO) defining standards for SQL?
Edit: List of implementation differences between common databases
Solution 1:
In the software industry you have some standards that are really standards, i.e., products that don't comply with them just don't work. File specifications fall into that category. But then you also have "standards" that are more like guidelines: they may defined as standards with point-by-point definitions, but routinely implemented only partially or with significant differences. Web development is full of such "standards", like HTML, CSS and "ECMAScript" where different vendors (i.e. web browsers) implement the standards differently.
The variation causes headaches, but the standardization still provides benefits. Imagine if there were no HTML standard at all and each browser used its own markup language. Likewise, imagine if there were no SQL standard and each database vendor used its own completely proprietary querying language. There would be much more vendor lock-in, and developers would have a much harder time working with more than one product.
So, no, ANSI SQL doesn't serve the same purpose as ANSI standards do in other industries. But it does serve a useful purpose nonetheless.
Solution 2:
Probably because standards conformance is of a low priority to database system purchasers. They are more interested in:
- compatibility with what they've already got
- performance
- price
- OS support
to name but a few factors.
The same is true of programming languages - very few (if any) compilers support every single feature of the current ANSI C and C++ standards.
As to why bother with standard, well most vendors do eventually bring standard support on board. For example, most vendors support more or less all of SQL89. This allows the vendor to tick a (relatively unimportant) check-box on their spec sheet and also allow people like me who are interested in writing portable code to do so, albeit having to forgo lots of bells and whistles.
Solution 3:
See the article "IS SQL A REAL STANDARD ANYMORE?" for a discussion about the current (2005) issues of the SQL standard.
Solution 4:
Indeed, the ANSI SQL standard is not often followed. Just read SO: most SQL threads never refer to the standard while, for instance, discussions on network protocols often include the actual quote, chapter and verse of the relevant RFC.
I always suspected that one of the reasons is the fact that the SQL standard is not freely distributable. Simply getting it is not trivial. Various unofficial copies float around.)
Another reason is that it is a very complicated text and poorly organized. It uses a strange vocabulary (such as "authID" instead "user"). You need books just to understand the standard ("A guide to the SQL standard", C.J. Date, Hugh Darwen - Addison-Wesley).
Solution 5:
I don't know the history of ANSI SQL specifically. But it seems that many times in software development, standards are written after the major players have already implemented their own proprietary versions of things. Once a company is invested in its own way of doing things, it's really hard to justify changing or removing features people have come to rely on just to adhere to a standard. Web standards are a primary example of this phenomenon.