Join two tables by using 3 columns and text function in freehand of the join


I need to join two tables by using 2 columns (%1,%2)  from the first one and 1 column (%3) from the second one.

Table 1:  column1 contain data like  PRJCDE and column 2 contain date like PRJCDE

Table 2 : column1 contain data like HOWPRJCDEPRJCDE

to joint de two tables i need to extract PRJCDEPRJCDE from column of table 2 (%3) and concatenate %1 and %2 of table 1 in order to set in freehand field of the join

Substring( HOWPRJCDEPRJCDE fom 4th position until the end to the string) = concatenation (%1 and %2).

I tried several text function Mid, lef, Right etc ... bu i continue to have error and the join can't be created.

Many thanks for your help and advice