Make a custom list box with content from two rows of a table

I have a DB with a FIRSTNAME and LASTNAME field. I would like to create a list box with the FIRSTNAME and LASTNAME as one line, so I thought I could make a request and make something like
select "NOM_MERE" + ' ' + "PRENOM_MERE" from "T_MERE", in sql it works but in the list box, it returns an error.

Hi,

What database are you using, embedded, or external, HSQL,…?

In the properties dialog of the list box you need to nominate which column value to store (Bound field) in the forms underlying table.
Usually that tends to be primary key, see attached screenshot. There are many posts with examples to be found.

oh I have to use pipe ! I didn’t knew it, thank you very much !