SQL Select only rows with Minimum Value on a Column with Where Condition

问题

Table:

| id | productId | orderIndex | rejected |
------------------------------------------
| 1  |  1        |   0        |   1      |
| 2  |  1        |   1        |   0      |
| 3  |  1        |   2        |   0      |
| 4  |  2        |   0        |   0      |
| 5  |  2        |   1        |   1      |
| 6  |  3        |   0        |   0      |

How can I select one row per productId with minimum orderIndex that not rejected?

Expected result:

| id | productId | orderIndex | rejected |
------------------------------------------
| 2  |  1        |   1        |   0      |
| 4  |  2        |   0        |   0      |
| 6  |  3        |   0        |   0      |

I tried this query, but don't recieved correct result:

SELECT id, productId, min(orderIndex)
FROM table
WHERE rejected = 0
GROUP BY productId

This one don't work also:

SELECT id, productId, min(orderIndex)
FROM (
    SELECT id, productId, orderIndex
    FROM table
    WHERE rejected = 0
) t
GROUP BY productId

回答1:

You can start by selecting the minimum orderIndex of products that are not rejected like this:

SELECT productId, MIN(orderIndex)
FROM myTable
WHERE rejected = 0
GROUP BY productId;

Once you have that, you can join it with your original table on the condition that productId and minOrderIndex match:

SELECT m.id, m.productId, m.orderIndex
FROM myTable m
JOIN(
  SELECT productId, MIN(orderIndex) AS minOrderIndex
  FROM myTable
  WHERE rejected = 0
  GROUP BY productId) tmp ON tmp.productId = m.productId AND tmp.minOrderIndex = m.orderIndex;

My query makes the assumption that there are no duplicate (productId, orderIndex) pairs. As long as those don't exist, this will work just fine. Here is an SQL Fiddle example.

回答2:

http://sqlfiddle.com/#!9/0196f/2

SELECT DISTINCT t.*
FROM table1 t
INNER JOIN (
SELECT productId, min(orderIndex) minIdx
FROM table1
WHERE rejected = 0
GROUP BY productId
  ) t1
ON t.productId = t1.productId
  AND t.orderIndex = t1.minIdx;

来源：https://stackoverflow.com/questions/29948321/sql-select-only-rows-with-minimum-value-on-a-column-with-where-condition

标签

mysql

greatest-n-per-group