When I ran the following queries in TDA...
DEFINE <variable> = '<value>';
SELECT * FROM <table> t WHERE t.<column> = '&&<varibale>' ;
I get the following Oracle error.
"ORA-00900: invalid SQL statement"
Currently TDA does not support the DEFINE clause. If you have Toad for Oracle, use it to run the query or use SQL PLUS to run the query.
Enhancement request has been submitted to Development for consideration in a future release of Toad for Data Analyst.