如何检测给定列是否仅具有NULL
值:
SELECT 1 -- no GROUP BY therefore use a literal
FROM Locations
HAVING COUNT(a) = 0
AND COUNT(*) > 0;
如何检测和删除仅包含空值的列?
如何检测给定列是否仅具有NULL
值:
SELECT 1 -- no GROUP BY therefore use a literal
FROM Locations
HAVING COUNT(a) = 0
AND COUNT(*) > 0;