Question

 CREATE TABLE table1
        (`id` int not null auto_increment primary key, `data` char(3),`subject` varchar(250)) ;

INSERT INTO table1
    (`id`, `data`,`subject`)
VALUES
    (1, 'xa','aad'),
    (2, 'ya','aac'),
    (3, 'yc','aae'),
    (4, 'zb','aaf'),
    (5, 'yb','aag'),
    (6, 'xc','aah'),
    (7, 'za','aai');

如表中所示，如何找到所有 不同的值，这些值以数据列中的第一个字母开头

例如：

select * from table1 where data like '%x%' limit 1;
select * from table1 where data like '%y%' limit 1;
select * from table1 where data like '%z%' limit 1;

进入单个查询并获取此输出，如下所示

输出

1, 'xa', 'aad'
2, 'ya','aac'
3, 'zb','aaf'

sql fiddle

Answer 1

组合DISTINCT和LEFT？但是不要忘记这种方法不能使用索引。

SELECT distinct(LEFT(`data`, 1)) first_letter, id, `data`, subject 
FROM table1
GROUP BY first_letter

http://sqlfiddle.com/#!9/08235/5/0

Answer 2

单一查询

select 
  id,
  data,
  LEFT(group_concat(subject order by id),LOCATE(',',group_concat(subject order by id)) - 1),
from table1
group by SUBSTRING(data, 1, 1)

Answer 3

您可以使用子查询获得每个组的第一个id

SELECT *
FROM table1
WHERE id IN (
select min(id) from table1
where data like '%x%'
OR data like '%y%'
OR data like '%z%'
GROUP BY left(data, 1)
)

Fiddle

Answer 4

使用UNION：

(select * from table1 where data like '%x%' limit 1) 
UNION ALL
(select * from table1 where data like '%y%' limit 1) 
UNION ALL
(select * from table1 where data like '%z%' limit 1) ;

updated fiddle

请注意：您必须将每个查询括在()中以限制每个查询的工作，否则您将只获得一行而不是三行。

另请注意，'%z%'会在任何位置为您提供包含z的值，而不仅仅是第一个字符。您需要使用LEFT(data, 1) = 'z'代替：

(select * from table1 where LEFT(data, 1) = 'x' limit 1 ) 
UNION ALL
(select * from table1 where  LEFT(data, 1) = 'y' limit 1) 
UNION ALL
(select * from table1 where  LEFT(data, 1) = 'z' limit 1 )

updated fiddle 2

如何在where语句mysql中找到不同的通配符

4 个答案: