Problems joining two sql tables and comparing if there is

I think the type of union you need here is a LEFT JOIN , which will give you NULL in the mismatches. Based on that same value, you can use CASE WHEN to show 1 or 0 evaluating some column of the table you will join with LEFT JOIN .

To group it or not I leave it to your criteria, and it would be necessary only in the case that there are several rows with the same id in the foreign table.

The query would be like this:

a With SQL Server

You can see a COMPLETE DEMO IN REXTESTER , operating on real data.

SELECT 
    c.cve_ventana, 
    c.nombre, 
    CASE WHEN r.fk_cve_Ventana IS NULL THEN 0 ELSE 1 END 'Existe' 
FROM catalogo c 
LEFT JOIN roles r
ON c.cve_ventana = r.fk_cve_Ventana;

b. With MySQL

You can see a COMPLETE DEMO IN REXTESTER , operating on real data.

In MySQL you can use IF , as follows:

SELECT 
    c.cve_ventana, 
    c.nombre, 
    IF(r.fk_cve_Ventana,'1','0') Existe 
FROM catalogo c 
LEFT JOIN roles r
ON c.cve_ventana = r.fk_cve_Ventana;

In a. as in b. the result would be:

Cve_Ventana | Nombre | Existe|
1           |carro   |1      | 
2           |llantas |0      |

You can do it in MySQL with one condition, if it exists it is 1 and if not 0.

SELECT c.* ,
IF (fk_cve_ventana = cve_ventana,1,0) AS existe
FROM catalogo c 
JOIN roles r ON r.fk_cve_ventana=c.cve_ventana
GROUP BY c.cve_ventana