在mysql中动态创建两列

Question

我在 mysql 查询中动态创建了两列。它们应该看起来像这样。

+------------------+
|Month    | toOrder|
+-------------------
|Nov-2014 |2014-11 |
--------------------
|Dec-2014 |2014-12 |
--------------------
|Jan-2015 |2015-01 |
--------------------
|Feb-2015 |2015-02 |
--------------------
|Mar-2015 |2015-03 |
--------------------
|Apr-2015 |2015-04 |
--------------------
|May-2015 |2015-05 |
--------------------
|Jun-2015 |2015-06 |
--------------------
|Jul-2015 |2015-07 |
--------------------
|Aug-2015 |2015-08 |
--------------------
|Sep-2015 |2015-09 |
--------------------
|Oct-2015 |2015-10 |
+------------------+

我正在使用这个查询

SELECT *
FROM    (SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 11 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 10 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 9 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 8 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 7 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 6 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 5 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 4 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 3 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 2 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 1 MONTH), '%b-%Y') as Month UNION
    SELECT DATE_FORMAT(now(), '%b-%Y') as Month) AS Months
LEFT JOIN
    (SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 11 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 10 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 9 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 8 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 7 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 6 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 5 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 4 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 3 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 2 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(DATE_SUB(now(), INTERVAL 1 MONTH), '%Y-%m') as toOrder UNION
    SELECT DATE_FORMAT(now(), '%Y-%m') as toOrder) AS toOrders
ON TRUE = TRUE

但我收到的输出与我的预期不同。

+------------------+
|Month    | toOrder|
+-------------------
|Nov-2014 |2014-11 |
--------------------
|Dec-2014 |2014-11 |
--------------------
|Jan-2015 |2014-11 |
--------------------
|Feb-2015 |2014-11 |
--------------------
|Mar-2015 |2014-11 |
--------------------
|Apr-2015 |2014-11 |
--------------------
|May-2015 |2014-11 |
--------------------
|Jun-2015 |2014-11 |
--------------------
|Jul-2015 |2014-11 |
--------------------
|Aug-2015 |2014-11 |
--------------------
|Sep-2015 |2014-11 |
--------------------
|Oct-2015 |2014-11 |
--------------------
|Nov-2014 |2014-12 |
--------------------
|Dec-2014 |2014-12 |
--------------------
|Jan-2015 |2014-12 |
--------------------
|Feb-2015 |2014-12 |
--------------------
|Mar-2015 |2014-12 |
--------------------
|Apr-2015 |2014-12 |
--------------------
|May-2015 |2014-12 |
--------------------
|Jun-2015 |2014-12 |
--------------------
|Jul-2015 |2014-12 |
--------------------
|Aug-2015 |2014-12 |
--------------------
|Sep-2015 |2014-12 |
--------------------
|Oct-2015 |2014-12 |
--------------------
|Nov-2014 |2015-01 |
+------------------+

我正在使用“toOrders”列，以便稍后使用我将来拥有的另一个 LEFT JOIN 执行 ORDER BY。

Answer 1

您正在执行没有 ON 子句的 JOIN。这称为交叉连接，并生成所有可能的输出组合。像这样的东西可能会产生你想要的东西。

SELECT DATE_FORMAT(Month,'%b-%Y') AS Month,
       DATE_FORMAT(Month,'%Y-%m') AS toOrder
FROM (
    SELECT DATE_SUB(now(), INTERVAL 11 MONTH) as Month      UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 10 MONTH) as Month      UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 9 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 8 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 7 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 6 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 5 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 4 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 3 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 2 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 1 MONTH) as Month       UNION ALL
    SELECT DATE_SUB(now(), INTERVAL 0 MONTH) as Month  
 ) months
ORDER BY months.Month

然而这个公式可能会在接近月底时产生奇怪的结果。我会更完全相信以下查询。

SELECT DATE_FORMAT(month.start - INTERVAL seq.seq MONTH,'%b-%Y') AS Month,
       DATE_FORMAT(month.start - INTERVAL seq.seq MONTH,'%Y-%m') AS toOrder
FROM (
   SELECT 11 AS seq UNION ALL
   SELECT 10 UNION ALL
   SELECT  9 UNION ALL
   SELECT  8 UNION ALL
   SELECT  7 UNION ALL
   SELECT  6 UNION ALL
   SELECT  5 UNION ALL
   SELECT  4 UNION ALL
   SELECT  3 UNION ALL
   SELECT  2 UNION ALL
   SELECT  1 UNION ALL
   SELECT  0
) seq
JOIN (
   SELECT CURRENT_DATE() - INTERVAL DAYOFMONTH(CURRENT_DATE()) - 1 DAY AS start
) month 
ORDER BY seq.seq DESC

那是因为

SELECT CURRENT_DATE() - INTERVAL DAYOFMONTH(CURRENT_DATE()) - 1 DAY AS start

很好地将今天的日期转换为当月的第一天。