除了某些值以外的组

Question

我试图创建一个（sqlite）查询，它将执行GROUP BY，但不会将任何值与“unknown”组合在一起。例如，我有表：

id | name | parent_id | school_id | 
1 | john | 1  | 1  | 
2 | john | 1  | 1  | 
3 | john | 1  | 1  | 
4 | nick | 2  | 2  | 
5 | nick | 2  | 2  | 
6 | nick | 3  | 3  | 
7 | bob  | 4  | 4  | 
8 | unknown | 5  | 5  | 
9 | unknown | 5  | 5  | 
10| unknown | 5  | 5  | 

与正确的查询“GROUP BY姓名，PARENT_ID，学校ID”我需要以下行返回：

id | name | parent_id | school_id | 
1 | john | 1  | 1  | 
3 | nick | 2  | 2  | 
4 | nick | 3  | 3  | 
5 | bob  | 4  | 4  | 
6 | unknown | 5  | 5  | 
7 | unknown | 5  | 5  | 
8 | unknown | 5  | 5  | 

任何帮助将不胜感激。谢谢！

Answer 1

你不能轻易做到这一点有一个说法，但你可以UNION两个语句

• GROUP所有但unknown
• 添加（UNION）的所有unknown的名单列表的结果

SQL Statement

SELECT MIN(id), name, parent_id, school_id 
FROM YourTable 
WHERE name <> 'unknown' 
GROUP BY 
     name, parent_id, school_id 
UNION ALL 
SELECT id, name, parent_id, school_id 
FROM YourTable 
WHERE name = 'unknown' 

请注意，我假设你已经张贴错unknown ID在你的结果

Answer 2

SELECT MIN(id), name, parent_id, school_id 
    FROM Table 
WHERE name <> 'unknown' 
GROUP BY name, parent_id, school_id 
UNION ALL 
SELECT id, name, parent_id, school_id 
    FROM Table 
WHERE name = 'unknown' 

Answer 3

SELECT 
    MIN(id) AS id, 
    IF(tmpname=id,"unknown",tmpname) AS name, 
    parent_id, 
    school_id 
FROM (
    SELECT 
    id,parent_id,school_id 
    IF(name="unknown",id,name) AS tmpname 
    FROM <tablename> 
) AS baseview 
GROUP BY tmpname 

Answer 4

作为一个单一的查询......

SELECT 
    MIN(id)   AS id, 
    name, 
    parent_id, 
    school_id 
FROM 
    yourTable 
GROUP BY 
    CASE WHEN name = 'unknown' THEN id ELSE 0 END, 
    name, 
    parent_id, 
    school_id 

或可能.. 。

GROUP BY 
    CASE WHEN name <> 'unknown' THEN name ELSE CAST(id AS VARCHAR(???)) END, 
    parent_id, 
    school_id 

-- Where VARCHAR(???) is the data type of the `name` field. 
-- Also assumes no value in `name` is the same as an id for an 'unknown' field 

两者都避免了UNION和两次解析表的开销，将其替换为稍微增加的复杂度GROUP BY。