[英]MySQL average of non-null columns
我已經為此煩惱了,但是我覺得可能有一個更清潔/更快/更好的解決方案,並且總是熱衷於學習:
UPDATE myTable SET fAvg =
(COALESCE(f1,0) + COALESCE(f2,0) + COALESCE(f3,0) + COALESCE(f4,0))
/
(
CASE WHEN f1 IS NOT NULL THEN 1 ELSE 0 END +
CASE WHEN f2 IS NOT NULL THEN 1 ELSE 0 END +
CASE WHEN f3 IS NOT NULL THEN 1 ELSE 0 END +
CASE WHEN f4 IS NOT NULL THEN 1 ELSE 0 END
)
那么,如何改善呢?
您可以利用MySQL在數字上下文中將布爾值視為整數的事實來簡化計數:
UPDATE myTable
SET fAvg = (COALESCE(f1,0) + COALESCE(f2,0) + COALESCE(f3,0) + COALESCE(f4,0)) /
((f1 IS NOT NULL) + (f2 IS NOT NULL) + (f3 IS NOT NULL) + (F4 IS NOT NULL));
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