I want to add the values that are in VLR_TOTAL where NOMBRE equals Expansion and NOMBRE equals Mantenimiento.
I have the following query:
SELECT SUM(VLR_TOTAL) FROM bodega_moviles WHERE NOMBRE = Expansion AND
NOMBRE = Mantenimiento
but throws me as a result
SUM(VLR_TOTAL)
NULL
Simple, change your operator AND to OR :
SELECT SUM(VLR_TOTAL)
FROM bodega_moviles
WHERE NOMBRE = 'Expansion' OR
NOMBRE = 'Mantenimiento'
By saying NOMBRE = [algún valor] AND NOMBRE = [algún otro valor] you are telling the query that the field NOMBRE should be equal to 2 different values, which can not be.
You can also use the IN operator in the following way to avoid redundancy:
SELECT SUM(VLR_TOTAL)
FROM bodega_moviles
WHERE NOMBRE IN ('Expansion', 'Mantenimiento')