Question

我得到如下结果

C1     C2   C3
10     2    T
10     3    E
10     6    S

我希望我的SELECT查询以这样的方式生成结果记录看起来像

C1     C2   C3
10     2    T
10     3    E
10     4
10     5
10     6    S

其中缺少记录的空白行。无法找出相同的答案。

原始查询：select C1, C2,C3 from Table

Answer 1

如果您的mysql版本高于8.0，则可以尝试使用cte RECURSIVE创建日历表，然后执行outer join

模式（MySQL v8.0）

CREATE TABLE T(
  C1 int, 
  C2 int,
  C3 varchar(5)
);


INSERT INTO T VALUES (10,2,'T');
INSERT INTO T VALUES (10,3,'E');
INSERT INTO T VALUES (10,6,'S');

查询＃1

WITH RECURSIVE CTE AS (
    SELECT C1,MIN(C2) minC2,MAX(C2) maxC2
    FROM T
    GROUP BY C1
    UNION ALL 
    SELECT C1,minC2 +1,maxC2
    FROM CTE
    WHERE minC2+1 <= maxC2
)
SELECT t1.C1,t1.minC2,t2.C3
FROM CTE t1 LEFT JOIN T t2 on t1.minC2 = t2.C2
ORDER BY C1,minC2;

| C1  | minC2 | C3  |
| --- | ----- | --- |
| 10  | 2     | T   |
| 10  | 3     | E   |
| 10  | 4     |     |
| 10  | 5     |     |
| 10  | 6     | S   |

View on DB Fiddle

Answer 2

您可以在数据库中创建一个序列号表，然后使用外部联接来填写C2缺少的行值。它对于其他查询也将非常有用，并且只占用很少的空间。

CREATE TABLE Numbers (Number INTEGER PRIMARY KEY);
INSERT INTO Numbers (Number) VALUES (1),(2),(3),(4),(5),(6) ...

然后：

SELECT T.C1, N.Number AS C2, T.C3 
FROM Numbers AS N LEFT OUTER JOIN T ON T.C2 = N.Number
WHERE N.Number BETWEEN (SELECT MIN(C2) FROM T) AND (SELECT MAX(C2) FROM T)
ORDER BY C2;

HTH

MySQL：实际上在SELECT语句中插入记录

2 个答案: