如何在 MySql 中将查询设置为变量

Question

我想查找每个组中最便宜和最贵商品的商品名称。但是我不知道为什么我在“SET @maxi := (SELECT A.ItName FROM tblqtdtl B INNER JOIN tblitem A ON A.ItCode = B.ItCode GROUP BY A.ItCode HAVING MAX(B.Price))”附近有SQL错误（1064）。也许我的 sql 代码

有问题或缺失

这就是我所期待的

vd码	视频名称	最便宜的商品	最便宜的价格	最贵的商品	最贵的价格
Vd001	DEF 纺织品	涤纶	2600	涤纶	2600
Vd003	MNO 纺织	涤纶	3228	丝绸	3950
Vd004	XYZ 纺织	涤纶	2800	丝绸	3480

这是我的代码

SET @mini :=(SELECT A.ItName FROM tblqtdtl B INNER JOIN tblitem A ON A.ItCode = B.ItCode 
                    GROUP BY A.ItCode HAVING MIN(B.Price)
                )
SET @maxi := (SELECT A.ItName FROM tblqtdtl B INNER JOIN tblitem A ON A.ItCode = B.ItCode 
                    GROUP BY A.ItCode HAVING MAX(B.Price)
                 )

SELECT V.VdCode, V.VdName, @mini AS 'Cheapest Item', MIN(B.Price) AS 'Cheapest Price', @maxi AS 'Most Expensive Item'
,MAX(B.Price) AS 'Most Expensive Price'
 
 FROM tblqthdr C 
 INNER JOIN tblvendor V ON C.VdCode = V.VdCode
 INNER JOIN tblqtdtl B ON C.DocNo = B.DocNo
 INNER JOIN tblitem A ON B.ItCode = A.ItCode
 WHERE V.ActInd='Y'
 GROUP BY V.VdCode

这是输入脚本

tblqdtl

INSERT INTO `tblqtdtl` (`DocNo`, `ItCode`, `Price`) VALUES
    ('QT001', 'It004', 38700.00),
    ('QT002', 'It002', 25600.00),
    ('QT003', 'It005', 21000.00),
    ('QT004', 'It004', 34000.00),
    ('QT005', 'It003', 32000.00),
    ('QT006', 'It002', 31780.00),
    ('QT007', 'It001', 28000.00),
    ('QT008', 'It002', 21800.00),
    ('QT009', 'It004', 32600.00),
    ('QT010', 'It002', 27500.00);

tblitem

INSERT INTO `tblitem` (`ItCode`, `ItName`, `ItCtCode`) VALUES
    ('Itestt001', 'Cotton', 'ALA'),
    ('It002', 'Polyester', 'SIN'),
    ('It003', 'Wool', 'ALA'),
    ('It004', 'Silk', 'ALA'),
    ('It005', 'Rayon', 'SIN');

tblqhdr

INSERT INTO `tblqthdr` (`DocNo`, `DocDt`, `VdCode`) VALUES
    ('QT001', '20180102', 'Vd003'),
    ('QT002', '20180203', 'Vd001'),
    ('QT003', '20180203', 'Vd002'),
    ('QT004', '20180207', 'Vd004'),
    ('QT005', '20180304', 'Vd003'),
    ('QT006', '20180401', 'Vd003'),
    ('QT007', '20180701', 'Vd005'),
    ('QT008', '20180902', 'Vd002'),
    ('QT009', '20180902', 'Vd005'),
    ('QT010', '20181203', 'Vd004');

tblvendor

INSERT INTO `tblvendor` (`VdCode`, `VdName`, `ActInd`) VALUES
    ('Vd001', 'ABC Textile', 'Y'),
    ('Vd002', 'DEF Textile', 'N'),
    ('Vd003', 'GHI Textile', 'Y'),
    ('Vd004', 'JKL Textile', 'Y'),
    ('Vd005', 'MNO Textile', 'N');

Answer 1

SELECT DISTINCT
       VdCode,
       VdName,
       FIRST_VALUE(ItName) OVER (PARTITION BY VdCode ORDER BY Price ASC) `Cheapest item`,
       MIN(Price) OVER (PARTITION BY VdCode) `Cheapest price`,
       FIRST_VALUE(ItName) OVER (PARTITION BY VdCode ORDER BY Price DESC) `Most expensive item`,
       MAX(Price) OVER (PARTITION BY VdCode) `Most Expensive Price`
FROM ( SELECT *
       FROM tblqthdr C 
       INNER JOIN tblvendor V USING (VdCode)
       INNER JOIN tblqtdtl B USING (DocNo)
       INNER JOIN tblitem A USING (ItCode)
       WHERE V.ActInd='Y' ) subquery

https://dbfiddle.uk/?rdbms=mysql_8.0&fiddle=53cade7afe509dcde6f259e5c5ae3fa3

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