Oracle MetaLink offers information regarding ORA-00937 as it is thrown with ORA-00903.  If you are experiencing ORA-00937 in this context, you may want to take a look at this information as it pertains to a bug.  ORA-00937 in bug 1988231 can occur in versions 8.1.7.4 to 10.2.0.4 of Oracle Enterprise in Microsoft Windows.  You will experience ORA-00937 with Microsoft OLEDB drivers  in response to executed queries using CURSOR_SHARING=FORCE and SIMILAR.   However, it is important to note that ORA-00937 will not get thrown using CURSOR_SHARING=EXACT or the irrespective CURSOR_SHARING parameter within SQL*Plus. 

The reason ORA-00937 is being thrown is bug 1988231 which occurs within the Microsoft OLEDB driver.  This being, Microsoft OLEDB drivers will throw ORA-00937 if you try to use CURSOR_SHARING=SIMILAR or FORCE to connect to your database.  To resolve this ORA-00937 bug, you should try using CURSOR_SHARING=EXACT or an Oracle ODBC driver.

Here is another example of a user encountering ORA-00903 from the OraFAQ forums:

Question:

I am trying to use a function that I created which will calculate my customer's bills, including discounts. 

However, every time I try to use the function, I receive ORA-00903.  Any suggestions?

Answer:

You are missing the GROUP BY clause in your function.  Try to take the SQL out and run it in SQL*Plus until it works again.  ORA-00937 can probably be detected during compile, but even if the function shows that it has been compiled, errors such as ORA-00937 may still be thrown.

Also, ORA-00937 may be occurring because of your SELECT clause.   Note that COUNT() and SUM() have to be grouped by all members in the SELECT clause.   

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