Question

我有一个MySQL地址表，其中包含以下列：

STATE, ZIPCODE, FLAG

给定state/zipcode组合可以有多行。我想确保对于每个给定的state/zipcode组合，只有一行有FLAG = 'P'。

我知道如何检查多行：

SELECT state, zipcode, flag, count(*) as numrecs
FROM addresses
WHERE flag = 'P'
group by state, zipcode
having numrecs > 1;

如何检查零条目 - state/zipcode组合中没有flag = 'P'的行？

Answer 1

你走在正确的轨道上，只需使用条件聚合：

SELECT state, zipcode, flag, count(*) as numrecs
FROM addresses
GROUP BY state, zipcode
HAVING coalesce(sum(flag = 'P'), 0) <> 1

或者，如果您愿意：

HAVING coalesce(sum(flag = 'P'), 0) = 0 or sum(flag = 'P') > 1

如果coalesce()可以是flag，并且给定的州/邮政编码组合只有NULL个标记，则需要NULL。

Answer 2

此查询应该为您提供违反标准的内容：

SELECT STATE, ZIPCODE, SUM(FLAG_COUNTER)
FROM (SELECT *, IF(FLAG='P', 1, 0) AS FLAG_COUNTER FROM addresses) tableWithCounter
GROUP BY STATE, ZIPCODE
HAVING SUM(FLAG_COUNTER) != 1

找出SQL表是否包含没有“标记”记录的条目

2 个答案: