mysql - 将两行的值合并为一

Question

    I have data like 
    user Id         colA        colB
    12              abc         NULL
    13              123         NULL
    13              NULL        567

    I want output like

    user Id         colA        colB
    12              abc         NULL
    13              123         567

Answer 1

尝试这个：

SELECT
user_Id, MAX(colA) colA, MAX(colB) colB
FROM tbl
GROUP BY user_Id

Answer 2

尝试这个

select user_id , 
if (colA = NULL , 0 , max(colA)) colA ,
if (colB = NULL, 0 , max(colB)) colB
from a
group by user_id

输出将是：

 USER_ID    COLA    COLB
   12       abc     (null)
   13       123     567

演示 SQLFIDDLE