Question

如果数据库表的列的值类似于＆＃39; A.B＆＃39;，＆＃39; C.D＆＃39;，＆＃39; A.C＆＃39;，我该怎么办？使用sql查询来查找具有＆＃39; A＆＃39;，＆＃39; B＆＃39;，＆＃39; C＆＃39;或者＆＃39; D＆＃39; （按字符分组）？

我期待结果是：

 _________________________
|  Characters| COUNT(*)   |
|*************************|
|    A       |    10      |
|*************************|
|    B       |    15      |
|************|************|
|    C       |     8      |
|************|************|
|    D       |     17     |
|____________|____________|

包含＆＃39; A＆＃39;的列的条目和＆＃39; B＆＃39; （比如＆＃39; A.B＆＃39;）应计入A＆＃39; A＆＃39;和＆＃39; B＆＃39;。

Answer 1

您可以使用模式匹配来完成此操作。这是一种方法：

select pattern.name, count(t.column)
from (select '%A%' as pattern, 'A' as name union all
      select '%B%' as pattern, 'B' as name union all
      select '%C%' as pattern, 'C' as name union all
      select '%D%' as pattern, 'D' as name
     ) patterns left join
     t
     on t.column like patterns.pattern
group by pattern.name;

请注意，这使用子查询为模式定义“派生表”。这种确切的语法可能不适用于所有数据库，但类似的东西应该有效。

Answer 2

你走了：

create table my_table (
  characters varchar(100)
);

insert into my_table (characters) values ('A.B');
insert into my_table (characters) values ('C.D');
insert into my_table (characters) values ('A.C');

select 'A' as letter, count(*) from my_table where characters like '%A%'
union select 'B', count(*) from my_table where characters like '%B%'
union select 'C', count(*) from my_table where characters like '%C%'
union select 'D', count(*) from my_table where characters like '%D%';

结果：

letter  count(*)
------  --------
A              2
B              1
C              2
D              1

计算给定列

2 个答案: