MySql transpose multiple rows into column - the most optimized way for large data?

问题

i want to transpose multiple rows to column.

This my table with data (about 20 mil.rows)

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

and I would like to get the following output:

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

etc..

Anybody know the fastest to do this (for about 20mil records)? Thanks very much!

回答1:

This should work well, make sure you have an index on phone.

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

回答2:

You can use variables to number the services within each group and use conditional aggregation to pivot your rows into columns.

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

来源：https://stackoverflow.com/questions/27575966/mysql-transpose-multiple-rows-into-column-the-most-optimized-way-for-large-dat

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mysql

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transpose