Firebird 到 MySQL 查询迁移 - Select 内连接子查询

Question

我有一个在我们的 Firebird SQL 数据模块中有效的查询。

我们迁移到 MySQL，我的所有查询都没有问题，除了这个。

请帮我解决这个问题。我得到一个错误：

Failed to Execute. Unknown column 'part.id' in 'on clause'

我的 Firebird 查询：

SELECT vendor.name AS "Vendor Name",
   Cast(Cast(vendorparts.lastdate AS date) AS CHAR(10)) AS "Last Date",
   CASE product.price
     WHEN '0' THEN 'CONFIRM'
     WHEN NULL THEN 'CONFIRM'
     ELSE Round(product.price, 2)
   end AS "D-Price",
   Cast(vendorparts.lastcost AS DECIMAL(18, 2)) AS "Last Cost",
   Cast(lowestcost.lowestcost AS DECIMAL(18, 2)) AS "Lowest Cost",
   Cast(highestcost.highestcost AS DECIMAL(18, 2)) AS "Highest Cost",
   part.num AS "Part Number",
   part.description AS "Part Description"

FROM   vendor,
       vendorparts,
       part,
       product
       INNER JOIN (SELECT vendorparts.partid,
                          Max(vendorparts.lastcost) AS Highestcost
                   FROM   vendorparts
                   GROUP  BY vendorparts.partid) AS highestcost
               ON part.id = highestcost.partid
       INNER JOIN (SELECT vendorparts.partid,
                          Min(vendorparts.lastcost) AS Lowestcost
                   FROM   vendorparts
                   GROUP  BY vendorparts.partid) AS lowestcost
               ON part.id = lowestcost.partid
WHERE  vendor.id = vendorparts.vendorid
       AND product.partid = part.id
       AND vendorparts.partid = part.id
       AND vendorparts.lastcost <> 0

除了在子查询中创建的 lowestcost 和 highestcost 外，所有表都在数据库中。

希望我的要求写清楚了。但总而言之——我需要迁移这个有效的 Firebird 查询以在 MySQL.

中工作

为什么这在 Firebird 中有效，但在 MySQL 中无效？

Answer 1

问题是 mySQL 中的 comma operator has lower precedence 比 join 运算符要大，因此 product inner join (subquery) on part.id = highestcost.partid inner join (subquery) on part.id = lowestcost.partid 联接在之前 part table 加入了表达式，因此出现错误消息。

用简单的 join 运算符替换逗号运算符并将连接条件从 where 子句移动到 on 子句，一切都会好起来的：

...
FROM   vendor
       inner join vendorparts on vendor.id = vendorparts.vendorid
       inner join part on vendorparts.partid = part.id
       inner join product on product.partid = part.id
       INNER JOIN (SELECT vendorparts.partid,
                          Max(vendorparts.lastcost) AS Highestcost
                   FROM   vendorparts
                   GROUP  BY vendorparts.partid) AS highestcost
               ON part.id = highestcost.partid
       INNER JOIN (SELECT vendorparts.partid,
                          Min(vendorparts.lastcost) AS Lowestcost
                   FROM   vendorparts
                   GROUP  BY vendorparts.partid) AS lowestcost
               ON part.id = lowestcost.partid
WHERE  vendorparts.lastcost <> 0

如果您有更多混合逗号运算符和显式连接的此类查询，那么您应该检查它们，因为即使 MySQL.[=18= 中没有语法错误，它们也可能会产生不同的结果]

Answer 2

此查询在 Firebird 3.0 及更高版本中也不起作用（请参阅 Support for Mixed-Syntax Joins is Gone）。原因是您将 SQL-89 样式连接与 SQL-92 样式连接组合在一起。

您需要重写查询以在所有地方使用显式连接，因此：

...
FROM   vendor 
   inner join vendorparts on vendor.id = vendorparts.vendorid
   inner join part on vendorparts.partid = part.id
   inner join product on product.partid = part.id
   INNER JOIN (SELECT vendorparts.partid,
                      Max(vendorparts.lastcost) AS Highestcost
               FROM   vendorparts
               GROUP  BY vendorparts.partid) AS highestcost
           ON part.id = highestcost.partid
   INNER JOIN (SELECT vendorparts.partid,
                      Min(vendorparts.lastcost) AS Lowestcost
               FROM   vendorparts
               GROUP  BY vendorparts.partid) AS lowestcost
           ON part.id = lowestcost.partid
WHERE vendorparts.lastcost <> 0

Answer 3

不要混用显式和隐式联接
避免在列和 table 名称中使用相同的别名（在此示例中 ai 指的是 t1 和 t2 ）并避免 AS for subselect table name

SELECT 
    vendor.name AS "Vendor Name",
    Cast(Cast(vendorparts.lastdate AS date) AS CHAR(10)) AS "Last Date",
    CASE product.price
     WHEN '0' THEN 'CONFIRM'
     WHEN NULL THEN 'CONFIRM'
     ELSE Round(product.price, 2)
    end AS "D-Price",
    Cast(vendorparts.lastcost AS DECIMAL(18, 2)) AS "Last Cost",
    Cast(lowestcost.lowestcost AS DECIMAL(18, 2)) AS "Lowest Cost",
    Cast(highestcost.highestcost AS DECIMAL(18, 2)) AS "Highest Cost",
    part.num AS "Part Number",
    part.description AS "Part Description"

FROM  vendor 
INNER JOIN vendorparts on vendor.id = vendorparts.vendorid AND vendorparts.lastcost <> 0 
INNER JOIN part on vendorparts.partid = part.id and 
INNER JOIN product on product.partid = part.id
INNER JOIN (SELECT vendorparts.partid,
                          Max(vendorparts.lastcost) AS Highestcost
                   FROM   vendorparts
                   GROUP  BY vendorparts.partid)  t1
               ON part.id = t1.partid
INNER JOIN (SELECT vendorparts.partid,
                          Min(vendorparts.lastcost) AS Lowestcost
                   FROM   vendorparts
                   GROUP  BY vendorparts.partid)  t2
               ON part.id = t2.partid

Firebird 到 MySQL 查询迁移 - Select 内连接子查询

Firebird to MySQL query migration - Select Inner Join Subquery

mysql

firebird

select

nested

join