如何在group by子句的一个列中计算多个列和多个不同的值

Question

我正在根据拖车的长度，门的类型和位置对拖车进行汇总。 然后对按门口长度类型分组的记录进行计数，然后上一层并按按门口长度类型分组的拖车进行计数。 最后，按批次位置计算拖车总数。

我已经试过这个例子。

http://sqlfiddle.com/#!9/23c89e/55

另外，我正在努力使分组和总计正确。 这确实可以正确计算拖车的长度（按门类型）-按批次位置。 但是，我无法进一步解决该问题。

这是select语句，使我走到了这一步。

SELECT g.length, g.doortype, g.location, g.total_location
FROM 
       ( SELECT length, doortype, location,  COUNT(*) AS total_location
         FROM trailers
         GROUP BY length, doortype, location
       ) AS g 

作为输出示例，它可以正确地按长度，门类型和位置进行计数，但是没有正确格式化和总计。

| length | doortype | location | total_location |
|--------|----------|----------|----------------|
|   28FT |  ROLL UP |    LOT C |              1 |
|   28FT |  ROLL UP |    LOT D |              2 |
|   28FT |    SWING |    LOT B |              1 |
|   45FT |  ROLL UP |    LOT B |              3 |
|   45FT |    SWING |    LOT B |              1 |
|   48FT |  ROLL UP |    LOT D |              1 |
|   48FT |  ROLL UP |    LOT E |              1 |
|   48FT |    SWING |    LOT A |              6 |
|   48FT |    SWING |    LOT B |              2 |
|   48FT |    SWING |    LOT C |              4 |
|   48FT |    SWING |    LOT E |              2 |

我正在尝试使输出看起来像这样。

| length | doortype | lot a | lot b | lot c | lot d | trailer total|
|--------|----------|-------|-------|-------|-------|--------------|
|   28FT |  ROLL UP |   1   |   0   |   1   |   0   |       2      |
|   28FT |  SWING   |   0   |   0   |   1   |   0   |       1      |
|   45FT |  ROLL UP |   1   |   5   |   0   |   0   |       6      |
|   45FT |  SWING   |   0   |   0   |   0   |   4   |       4      |
|   48FT |  ROLL UP |   2   |   1   |   0   |   1   |       4      |
|   48FT |  SWING   |   0   |   0   |   1   |   1   |       2      |
|------------------------------------------------------------------|
            TOTAL   |   4   |   6   |   3   |   6   |       19     |

Answer 1

使用位置作为过滤器，并使用总和来合并其计数。

SELECT 
    length, 
    doortype, 
    SUM(IF(location = 'LOT A', 1, 0)) Lot_A,
    SUM(IF(location = 'LOT B', 1, 0)) Lot_B,
    SUM(IF(location = 'LOT C', 1, 0)) Lot_C,
    SUM(IF(location = 'LOT D', 1, 0)) Lot_D,
    COUNT(0) AS Trailer_Total
FROM trailers
GROUP BY length, doortype;

Answer 2

它将创建一些额外的门类型为NULL的行，您可以在循环浏览时忽略该行

            SELECT tab.*
            FROM (SELECT 
                COALESCE(length, 'All length') AS length,
                doortype, 
                SUM(IF(location = 'LOT A', 1, 0)) Lot_A,
                SUM(IF(location = 'LOT B', 1, 0)) Lot_B,
                SUM(IF(location = 'LOT C', 1, 0)) Lot_C,
                SUM(IF(location = 'LOT D', 1, 0)) Lot_D,
                COUNT(case location when 'LOT E' then null ELSE 1 end) AS Trailer_Total    
            FROM trailers
            GROUP BY length, doortype WITH ROLLUP
            )tab
            where tab.doortype IS NOT NULL OR tab.length = 'All length'
            order by tab.length, tab.doortype