How to use AND in a CASE sqlite statement for validation check?

Question

I'v a SQLite database and I want to generate a kind of validation check. The main target is to compare three fields in a table. If stnd_sht has the value 'nicht gegeben' then there should be a entry either in mass_sof of in mass_6m, if not then plausibility is not given.

So far I tried the following:

SELECT 
b.baum_id AS baum_id,

CASE 
WHEN b.stnd_sht ='nicht gegeben' AND b.mass_sof IS NULL  THEN 'fehler'
WHEN b.stnd_sht ='nicht gegeben' AND b.mass_6m IS NULL THEN 'fehler'
ELSE 'plausibel' END AS plaus

FROM baeume b;

and...

SELECT 
b.baum_id AS baum_id,

CASE WHEN (b.mass_sof IS NULL OR b.mass_6m IS NULL) AND b.stnd_sht ='nicht gegeben' THEN 'fehler'
ELSE 'plausibel' END AS plaus

FROM baeume b;

Everything works fine without any AND or OR operator but as I add additional expressions the result is not correct. Is the AND operator not supportet by the CASE statement, or am I totaly wrong and the statement needs another structure or has to be more complex? Thanks in advance, Patrick

Answer 1

These expressions are syntactically correct, but do not correspond to the explanation.

Sometimes, it helps to reverse a logical condition. According to the explanation, there is an error if stnd_sht is nicht gegeben and if both the mass_sof and mass_6m values are NULL.

This would correspond to the following expression:

SELECT baum_id,
       CASE WHEN stnd_sht = 'nicht gegeben' AND
                 mass_sof IS NULL           AND
                 mass_6m IS NULL
            THEN 'fehler'
            ELSE 'plausibel'
       END AS plaus
FROM baeume;

This could be simplified a little:

SELECT baum_id,
       CASE WHEN stnd_sht = 'nicht gegeben'          AND
                 COALESCE(mass_sof, mass_6m) IS NULL
            THEN 'fehler'
            ELSE 'plausibel'
       END AS plaus
FROM baeume;