Question

I have a table with many lines. I need select several (no more than three) lines with certain values and one more. Moreover, need ORDER BY id DESC and required line position before other. Example:

id | name | group
-----------------
1  | One  | null
2  | Two  | null
3  | Three| 2
4  | Four | 3
5  | Five | 1
6  | Six  | 2

I need lines with group == 2 (no more than three) and line with id == 2. Result:

id | name | group
-----------------
2  | Two  | null
3  | Three| 2
6  | Six  | 2

Line with id == 2 must be selected, other lines - no more than three. If I use WHERE id = 2 OR group = 2 LIMIT 4 than if exist more than 4 lines with group == 2, then required line with id == 2 not selected.

How solve the problem in one SQL-request?

Answer 1

您可以尝试使用UNION。另请注意，group是MySQL的保留字。

SELECT aa.* 
FROM (
    SELECT id, firstname, lastname
    FROM user
    WHERE id IN (1, 2, 3, 4)
    LIMIT 2

    UNION ALL

    SELECT id, firstname, lastname
    FROM user
    WHERE id = 5

) AS aa

Answer 2

select * from table_name where id=2 
union all 
select * from table_name where group=2

Select one fixed line and several arbitrary

2 个答案: