Question

我想将多行转置为列。

这是我的数据表（约20密尔）

PHONE      SERVICE
0000000    service1
0000000    service2
0000000    service3
1111111    service1
1111111    service4
2222222    service5

我希望得到以下输出：

PHONE      SC1       SC2       SC3       SC4   SC5
0000000    service1  service2  service3  NULL  NULL
1111111    service1  service4  NULL      NULL  NULL
2222222    service5  NULL      NULL      NULL  NULL

等。

任何人都知道最快这样做（约20mil记录）？非常感谢！

Answer 1

这应该很有效，请确保您在phone上有索引。

SELECT phone,
       SUBSTRING_INDEX(services, ',', 1) SC1,
       if(service_count >= 2, SUBSTRING_INDEX(SUBSTRING_INDEX(services, ',', 2), ',', -1), NULL) SC2,
       if(service_count >= 3, SUBSTRING_INDEX(SUBSTRING_INDEX(services, ',', 3), ',', -1), NULL) SC3,
       if(service_count >= 4, SUBSTRING_INDEX(SUBSTRING_INDEX(services, ',', 4), ',', -1), NULL) SC4,
       if(service_count >= 5, SUBSTRING_INDEX(SUBSTRING_INDEX(services, ',', 5), ',', -1), NULL) SC5
FROM (SELECT phone, GROUP_CONCAT(service) AS services, COUNT(*) as service_count
      FROM phones
      GROUP BY phone) AS x

DEMO

Answer 2

您可以使用变量对每个组中的服务进行编号，并使用条件聚合将行转移到列中。

select phone,
    max(case when rn = 1 then service end) sc1,
    max(case when rn = 2 then service end) sc2,
    max(case when rn = 3 then service end) sc3,
    max(case when rn = 4 then service end) sc4,
    max(case when rn = 5 then service end) sc5
from (
    select phone,service,
      @rowNum := if(@prevPhone = phone,@rowNum+1,1) rn, 
      @prevPhone := phone
    from mytable 
    cross join (select @prevPhone := null, @rowNum := 1) c 
    order by phone, service
) t1 group by phone

MySql将多行转换为列 - 大数据最优化的方式？

2 个答案: