You could use a COMMAND for the data source. You supply the SQL so something like
SELECT T1.*, T2.*
FROM T1 INNER JOIN T2 ON
T1.NumberField = ToNumber(T2.TextField)
Another way would be to add the tables to the report and not link them.
Use the SELECT EXPERT to link them as
{T1.NumberField} = ToNumber({T2.TextField})
mlmcc