MySQL order by primary key - mysql

Question

Some SQL servers allow for a generic statement such as ORDER BY PRIMARY KEY. I don't believe this works for MySQL, is there any such workaround that would allow for automated selects across multiple tables or does it require a lookup query to determine the primary key?
The workaround I have been working on involves calling a SHOW COLUMNS FROM before running the query. Is there a more efficient way of doing this? Can MySQL determine the primary key of a table during the select process?
Update: There is no official way of doing this in MySQL or SQL in general as Gordon pointed out. SAP has custom functionality for it. There are workarounds, such as working with SHOW COLUMNS FROM table or the information_schema as John pointed out.

Answer 1

MySQL generally pulls data out by insertion order which would be by primary key, but that aside you technically can do the same thing if you pull out the primary key column name and put it in an order by
SELECT whatever FROM table
ORDER BY
( SELECT `COLUMN_NAME`
FROM `information_schema`.`COLUMNS`
WHERE (`TABLE_SCHEMA` = 'dbName')
AND (`TABLE_NAME` = 'tableName')
AND (`COLUMN_KEY` = 'PRI')
);
For composite keys you can use this
SELECT whatever FROM table
ORDER BY
( SELECT GROUP_CONCAT(`COLUMN_NAME` SEPARATOR ', ')
FROM `information_schema`.`COLUMNS`
WHERE (`TABLE_SCHEMA` = 'dbName')
AND (`TABLE_NAME` = 'tableName')
AND (`COLUMN_KEY` = 'PRI')
);
Permission for information schema access from the DOCS
Each MySQL user has the right to access these tables, but
can see only the rows in the tables that correspond to objects for
which the user has the proper access privileges. In some cases (for
example, the ROUTINE_DEFINITION column in the
INFORMATION_SCHEMA.ROUTINES table), users who have insufficient
privileges see NULL. These restrictions do not apply for InnoDB
tables; you can see them with only the PROCESS privilege.
The same privileges apply to selecting information from
INFORMATION_SCHEMA and viewing the same information through SHOW
statements. In either case, you must have some privilege on an object
to see information about it.
SETUP:
CREATE TABLE some_stuff (
firstID INT,
secondID INT,
username varchar(55),
PRIMARY KEY (firstID, secondID)
) ;
QUERY:
SELECT GROUP_CONCAT(`COLUMN_NAME` SEPARATOR ', ')
FROM `information_schema`.`COLUMNS`
WHERE (`TABLE_SCHEMA` = 'dbName')
AND (`TABLE_NAME` = 'some_stuff')
AND (`COLUMN_KEY` = 'PRI');
OUTPUT:
+--------------------------------------------+
| GROUP_CONCAT(`COLUMN_NAME` SEPARATOR ', ') |
+--------------------------------------------+
| firstID, secondID |
+--------------------------------------------+

Answer 2

SAP does, indeed do this (http://help.sap.com/saphelp_nw04s/helpdata/en/fc/eb3a53358411d1829f0000e829fbfe/content.htm). SQL Server is also based on Sybase, and I don't think Sybase supported this functionality. There are many limitations on the syntax.
On a query on one table with a primary key, no explicit order by, and no where conditions, MySQL will generally return the results in primary key order. You cannot depend on this functionality, but it might be good enough for your system.
The big issue would be the use of indexes for the where clause. If there are no indexes on the table, you don't have to worry about it. If there are, you could possibly emulate the behavior with a materialized view:
select t.*
from (select t.*
from table t
) t
where <where clause here>;
Another option is to force the database engine to use the primary key index. You can do this by using a force index hint. The issue is that you need to know the name of the index.