I have 2 tables, one list all the projects and the other provide a list of task for the project. In the task table we have a field call LANG_CODE. Basically the LANG_CODE is EN for English and CF for French and null value if any is selected.

In the Select expert for the project I created a parameter field to enter the project number

{?Project}

If I want to query for all EN in the project I used this formula that work well

{LDMXA.EIACODXA} = {?Project} and
{LDMCC.LANG_CODE} = "EN"

When I try to modify the formula to include the null value with this formula it run the query but on all project not the one I specify in my parameter field. This is my formula

{LDMXA.EIACODXA} = {?Project} and
isnull({LDMCC.LANG_CODE}) or {LDMCC.LANG_CODE} = "EN"

I search the web for a solution with no result

Thank for the answer. I had to add the () as follow

(isnull({LDMCC.LANG_CODE}) or {LDMCC.LANG_CODE} = "EN") and
{LDMXA.EIACODXA} = {?Project}

Everything work perfectly