Question

我有一张类似下面的表格：

timeUnit    country    name    count
    1          UK      Fred     12
    1          GE      Bob      1
    1          GE      John     3
    2          UK      Fred     6
    2          GE      Bob      5
    2          GE      John     8
    3          UK      Fred     4
    3          GE      Bob      6
    3          GE      John     5
    4          UK      Fred     4
    4          GE      Bob      8
    4          GE      John     9
    4          UK      Philip   6
    5          UK      Fred     3
    5          GE      Bob      2
    5          GE      John     1
    5          UK      Philip   5
    6          UK      Fred     8
    6          GE      Bob      9
    7          UK      Fred     8
    7          GE      Bob      9
    7          GE      John     8
    7          UK      Philip   6
    8          UK      Fred     5
    8          GE      Bob      1
    8          GE      John     1

我想做的是相当于：

SELECT * FROM table1 WHERE country ='UK'

但是结果包括缺少对于计数为零的Philip的timeUnit结果，即返回：

timeUnit    country    name    count
   1           UK      Fred      12
   1           UK      Philip    0
   2           UK      Fred      6
   2           UK      Philip    0
   3           UK      Fred      4
   3           UK      Philip    0
etc...

我有一种感觉，这应该可以通过某种形式的临时表或查询加入，但真的很难理解它。

感谢您的帮助。

Answer 1

如果name coluimn是唯一的名称来源，则可以执行子查询以从表中获取所有不同的名称，然后LEFT JOIN子查询的结果到主表，使用聚合以获取您正在寻找的值。

SELECT
    t.timeUnit AS timeUnit,
    t.country AS country,
    names.name AS name,
    SUM(t.`count`) AS `count`
FROM (
    SELECT DISTINCT name FROM table1
) AS names
LEFT JOIN table1 AS t
    ON names.name = t.name
WHERE country = ?
GROUP BY timeUnit, name

Answer 2

假设timeUnit，name值全面包含在您的表中，您可以使用如下查询：

SELECT t1.timeUnit, 
       COALESCE(t3.country, 'UK') AS country, 
       t2.name,  
       COALESCE(SUM(count), 0) AS count
FROM (
   SELECT DISTINCT timeUnit
   FROM Table1) AS t1
CROSS JOIN (
   SELECT DISTINCT name
   FROM Table1
   WHERE country = 'UK') AS t2
LEFT JOIN (
   SELECT timeUnit, country, name, count
   FROM Table1
   WHERE country = 'UK'
) AS t3 ON t1.timeUnit = t3.timeUnit AND t2.name = t3.name
GROUP BY t1.timeUnit, t3.country, t2.name
ORDER BY t1.timeUnit, t2.name

CROSS JOIN用于创建包含timeUnit情况下所有可能（name，country = 'UK'）对的内联表。对此表执行LEFT JOIN会得到一个结果集，其中包含所有可能的（timeUnit，name）对以及相应的计数。

Demo here

强制SQL结果填写缺失值

2 个答案: