消除mysql中的空值

Question

我有这种桌子：

MongoDB shell version v3.6.3
connecting to: mongodb://127.0.0.1:27017
2018-10-01T17:38:22.425+0000 W NETWORK  [thread1] Failed to connect to 127.0.0.1:27017, in(checking socket for error after poll), reason: Connection refused
2018-10-01T17:38:22.426+0000 E QUERY    [thread1] Error: couldn't connect to server 127.0.0.1:27017, connection attempt failed :
connect@src/mongo/shell/mongo.js:251:13
@(connect):1:6
exception: connect failed

我想消除空值。我希望它像这样：

Column 1 | Column 2 | Column 3 | Column 4
----------------------------------------
Value 1  |  null    | null     | null    
null     |  Value 2 | null     | null    
null     |  null    | Value 3  | null  
null     |  null    | null     | Value 4

任何帮助将不胜感激。谢谢。

Answer 1

似乎您要聚合：

select max(col1), max(col2), max(col3), max(col4)
from table t;

假设您有支持的专栏，那么您可以：

select col, max(col1), max(col2), max(col3), max(col4)
from table t
group by col;