SQL Statement Syntax Differences - mysql

Question

I was wondering what types of things usually vary between SQL implementations when looking at the query statements. One thing that I thought was the use of IS NULL in the WHERE clause. See bleow for example. I'm writing a query statement parser that handles the statement and queries in a custom language and need to account for most of the general differences between the more widely used SQL products.
Oracle Syntax:
SELECT * FROM TABLE WHERE COLUMN_A IS NULL
SELECT * FROM TABLE WHERE COLUMN_A IS NOT NULL
MySQL Syntax?
SQL Server Syntax?

Answer 1

I'm not sure you're going to find a definitive list of all differences. A few things I can think of off the top of my head:
MySQL uses LIMIT while SQL Server uses TOP.
SQL Server is much stricter on GROUP BY operations than MySQL, requiring that all non-aggregated columns from the SELECT appear in the GROUP BY clause.
SQL Server supports a proprietary UPDATE FROM and DELETE FROM syntax that goes beyond the ANSI standard.
Functions that exist in one system but not another. MySQL has FIND_IN_SET and GROUP_CONCAT that don't exist in SQL Server. Likewise, SQL Server has ROW_NUMBER() that doesn't exist in MySQL.

Answer 2

The IS NULL / IS NOT NULL syntax is ANSI standard SQL, and supported in all three of those RDBMS as you have listed it for Oracle.

Answer 3

IS NULL and IS NOT NULL is the same pretty much everywhere. The main differences for basic queries would relate to function calls, and those are vastly different so you'll have to be more specific there.

Answer 4

There are plenty of things that vary between different RDMBS implementation. Here's a simple example which doesn't use any specific function:
In Oracle, you can update table A from data in table B as follows:
UPDATE A
SET (COL1,COL2) = (SELECT B.COL3, B.COL4 FROM B WHERE B.COL5 = A.COL6)
WHERE A.COL7 = 3
AND EXISTS (SELECT 1 FROM B WHERE B.COL5 = A.COL6);
But in SQL Server the same task can be done as follows:
UPDATE A
SET COL1 = B.COL3, COL2 = B.COL4
FROM B
WHERE B.COL5 = A.COL6
AND A.COL7 = 3;
Additionally, the Oracle syntax is invalid in SQL Server and vice versa, so you can't settle for a common denominator. Writing a parser for this particular syntax is a challenge, so a general parser seems to be a highly non-trivial task.

Answer 5

You can apply both queries to all the rdbms. This is standard ansi.

Answer 6

About a decade ago I bookmarked a link, long since broken, to a document entitled, "Levels of Vendor Compliance with ANSI SQL". I've kept it so I can think, "Ah, how quaint." The Standard is now ISO (I = international) and not just ANSI (A = USA). Nobody tries to document this kind of thing for more than one SQL product anymore.
All vendors pay close attention to the SQL Standard and will declare level compliance on a feature-by-feature basis. Even when no such declaration is forthcoming you know they have read the Standard spec, even if it means a concious decision to extend or to do things completely differently. If you are interested in portability then get used to writing Standard SQL that is implemented by, or similar to syntax in, the SQL products you wish to target.
Taking mySQL and SQL Server as examples. I would guess that some mySQL features (e.g. ORDER BY LIMIT) are closer to Standards than SQL Server is (TOP) because mySQL have come to the party later and actually had a Standard spec to follow and no legacy version to be compatible with. I would guess that other features in mySQL (update on duplicate key) are further from Standards (SQL Server extends MERGE from Standards) because they wanted something easier to implement and simpler users. I would a guess some mySQL features are close to those in SQL Server to be able to poach users!