Question

我正在尝试运行下面的查询并继续得到除以0的错误。有时候除数中的平均值可以是0.如果我使用HAVING语句，其中平均值> 0，则相同的查询有效。 0.但是，那些有效值将从结果中排除。

SELECT B.facility_desc Well,
B.facility_id   "Facility ID",
( Cast(C.value AS NUMERIC(6, 0)) ),
( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ),
( ( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ) - ( Cast(C.value AS NUMERIC(6, 0)) ) ),
CASE
WHEN ( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ) = 0 THEN NULL
ELSE (( ( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ) - ( Cast(C.value AS NUMERIC(6, 0)) ) ) / ( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ) )
END,
D.desc
FROM   houston_vhs.historicalvalues A
LEFT JOIN houston_fac.fac_header B
ON LEFT(A.pointidlong, 10) = B.facility_id
LEFT JOIN houston_uis.realtimevalues C
ON LEFT(A.pointidlong, 10) = C.facilityid
LEFT JOIN houston_trs.table_header_record D
ON B.facility_table5 = D.table_entry
WHERE  A.pointidlong LIKE 'DIMO_N8%_VGY'
AND A.pointtime > Now() - 7
AND A.unreliableflag = 'N'
AND B.facility_desc <> ''
AND B.facility_is_active = 'Y'
AND C.udc = 'RGAS'
AND C.value <> ''
GROUP  BY B.facility_desc,
B.facility_id,
C.value,
D.desc
ORDER  BY ( ( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ) - ( Cast(C.value AS NUMERIC(6, 0)) ) ) ASC

我已尝试将CASE语句的顺序更改为值＆gt; 0然后等式，如果不是那么NULL无济于事。我也尝试过使用NULLIF，这也是不行的。任何见解都表示赞赏。

Answer 1

通常，SQL会依次评估CASE表达式。但是，在存在聚合函数的情况下，此规则变得更加模糊 - 因为需要首先计算聚合表达式。

一个简单的解决方法是使用nullif()：

 (( ( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ) - ( Cast(C.value AS NUMERIC(6, 0)) ) ) / nullif( Avg(DISTINCT( Cast(A.value AS NUMERIC(6, 0)) )) ), 0 )

我想指出：我已经使用SQL多年（数十年），我从来没有理由使用AVG(DISTINCT)。这表明您的JOIN正在复制数据，此修复程序不是正确的解决方法。

除以0错误和CASE - SQL

1 个答案: