I found a situation I can't explain. I have the following SQL:

SELECT NOCLIENT,NOCAT,NUMERO,NOMEMBER,NOPARENT,NOTHREAD,ADDDATE,ADDHEURE,TITLE,.T. AS FLAG,1;
 FROM THREAD WHERE NoClient=5 AND NUMERO>=600000;
UNION SELECT NOCLIENT,NOCAT,NUMERO,NOMEMBER,NOPARENT,NOTHREAD,ADDDATE,ADDHEURE,TITLE,.T. AS FLAG,0;
 FROM THREAD WHERE NoClient<>5 AND NUMERO>=600000;
 ORDER BY 11 DESCENDING,1,2,6,5 INTO CURSOR TEMP READWRITE

The only way to make that work is to use an ORDER BY clause with numeric references. As soon as I put the UNION clause in it, I am forced to use numeric references for the SQL. Why is that?