MySQL获取默认或最小行的值

Question

I have a table with structure

ID|GROUP_ID|DEFAULT|VALUE
13|      10|      0|   20
14|      11|      0|   30
15|      10|      0|   40
16|      10|      1|   50
17|      11|      0|   60

I want to get one row for each GROUP_ID by rule:

if GROUP_ID has row with DEFAULT = 1 I have to get this row

if GROUP_ID doesn't have row with DEFAULT = 1 I have to get row with MIN(VALUE)

For above data result should be:

16|10|1|50
14|11|0|30

How can I do this with MySql?

Answer 1

You can do this in MySQL. Here is one method:

select t.*
from t
where t.id = (select t2.id
              from t t2
              where t2.group_id = t.group_id
              order by (default = 1) desc, value asc
              limit 1
             );

The subquery orders all rows for a given group based on your rules. The expression (default = 1) desc , put the default values first. In a numeric context, MySQL treats boolean values as numbers, with "1" for true and "0" for false (hence the desc ).