JDBC SQL:Where is the detailed specification?

Question

Everybody loves to mention how JDBC abstracts away vendor-specific differences between SQLs to present a single SQL flavor that would work against a whole slew of them.

But no book or reference on JDBC ever mentions a (detailed) specification or even a decent, user-space coverage of this SQL supported by (a specific version of) JDBC, say JDBC 4.1!

So, what ends up happening (at least with me) is that, if I'm working with MySQL, I must refer to the MySQL reference manual and then try to guard myself against accidentally using MySQL-specific features. For writing portable SQL (at least at the level supported by the JDBC driver version I'm using), I would rather prefer to refer to a JDBC spec or to an SQL spec directly instead of referring to MySQL, PostgresQL, etc.

Is the SQL standard itself (2008, 2003, etc), on which a particular version of JDBC is based, freely available? Or, do I have to shell out $$ to get a copy?

Answer 1

There is no "JDBC SQL", just ISO SQL and the vendor implementations of it. JDBC defines the interface for talking to SQL databases, it's a different layer to the query language its self.

The reference for JDBC its self is the JSR documentation:

• JDBC 4.0
• JDBC 4.1

Unfortunately the official SQL standards are expensive and must be purchased from the ISO.

You can find late-stage drafts that're perfectly good for reference when you're not trying to develop a conforming implementation here among other places.

The SQL spec isn't the most friendly and readable of things, so in practice it's a good idea to use vendor documentation that's actually intended to be read by human beings. You can compare a couple of vendor docs or fall back on the standard doc when uncertainty arises.

Standard compliance with the spec isn't exactly ideal across DBs; writing code strictly to the spec doesn't necessarily mean it'll actually work. For example, MySQL doesn't impliment window functions or common table expressions, PostgreSQL doesn't implement SQL/PSM (instead offering PL/PgSQL) or the CALL statement; most vendors use different ways of specifying auto-increment columns or sequence generators; etc etc etc.

Please don't use the w3schools SQL guides, they're severely outdated, wrong, fail to differentiate between vendor extensions and the standard, and should generally be avoided. I mention them because w3schools tends to come up quite high in search rankings - back in the day they used to actually be useful.

Answer 2

You can download the JDBC 4.1 specification from http://download.oracle.com/otndocs/jcp/jdbc-4_1-mrel-spec/index.html but this only covers JDBC itself, not SQL. The specification is more a description of the interface; it does expect databases to support some level of the SQL standards, but don't expect to find more information than a reference to the SQL standard if it comes to the requirements to queries.

You usually need to use the database specific SQL anyway, because even though there is a SQL standard, database vendors don't implement them to the letter. JDBC itself defines some escapes to bridge the gaps, but as far as I know, they are hardly ever used. Drivers also - usually - don't translate standard SQL to database specific SQL if the database doesn't support the standard SQL.

If you want to look at the official SQL standard, you need to buy it from ISO or your country-specific ISO representative. That said, with some searching you can find and download draft versions of the specification for free. I am not sure how helpful that is though, as the SQL standard documents are not intended as a reference manual, but meant to be a formal description and goes really deep in details that are only relevant to an implementer.