帮我改写这个查询

Question

我有这个问题:

SELECT diamond_id, carat, clarity, color, cut,
    CASE clarity
        WHEN "FL" THEN 0
        WHEN "IF" THEN 1
        WHEN "VVS1" THEN 2
        WHEN "VVS2" THEN 3
        WHEN "VS1" THEN 4
        WHEN "VS2" THEN 5
        WHEN "SI1" THEN 6
        WHEN "SI2" THEN 7
        WHEN "I1" THEN 8
        WHEN "I2" THEN 9
        WHEN "I3" THEN 10
        ELSE -1
    END AS clarity_score,
    CASE cut
        WHEN "ideal" THEN 0
        WHEN "excellent" THEN 1
        WHEN "very good" THEN 2
        WHEN "good" THEN 3
        WHEN "fair" THEN 4
        WHEN "poor" THEN 5
        ELSE -1
    END AS cut_score    
    FROM rapnet_diamonds
 WHERE 
    shape IN ("round","princess","oval") 
 AND (carat BETWEEN ".1" AND "5") 
 AND (color BETWEEN "D" AND "Z") 
 AND (clarity_score BETWEEN "0" AND "10") 
 AND (cut_score BETWEEN "0" AND "5")

如您所见,我即时生成clarity_score和cut_score列,因此我可以在WHERE子句中使用它们.

首先,这给了我一个错误,告诉我clarity_score不存在.所以我想也许这是我需要使用HAVING的情况之一？

所以我把where子句改为:

WHERE 
    shape IN ("round","princess","oval") 
 AND (carat BETWEEN ".1" AND "5") 
 AND (color BETWEEN "D" AND "Z") 
HAVING 
    (clarity_score BETWEEN "0" AND "10") 
 AND (cut_score BETWEEN "0" AND "5")

我没有错误,但0结果......这应该返回超过100K.所以我在某处写错了？

然而,在你开始重写之前,我不想选择那两个生成的字段,有没有办法可以编写它,所以我没有检索这两个字段,只是在where子句中使用它们？

Answer 1

您可以执行以下操作.

创建两个查找表

create table clarity_lookup 
    (clarity_score int,
    clarity char(5))

create table cut_lookup 
    (cut_score int,
    cut char(10))

使用数据加载查找表

INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (0, 'FL')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (1, 'IF')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (2, 'VVS1')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (3, 'VVS2')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (4, 'VS1')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (5, 'VS2')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (6, 'SI1')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (7, 'SI2')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (8, 'I1')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (9, 'I2')
INSERT INTO clarity_lookup (clarity_score, clarity) VALUES (10, 'I3')

INSERT INTO cut_lookup (cut_score, cut) VALUES (0, 'ideal')
INSERT INTO cut_lookup (cut_score, cut) VALUES (1, 'excellent')
INSERT INTO cut_lookup (cut_score, cut) VALUES (2, 'very good')
INSERT INTO cut_lookup (cut_score, cut) VALUES (3, 'good')
INSERT INTO cut_lookup (cut_score, cut) VALUES (4, 'fair')
INSERT INTO cut_lookup (cut_score, cut) VALUES (5, 'poor')

您的查询将如下所示.总之,您可以CASE根据分数将表示原始子句中的数据的新表连接到菱形表,但在SELECT子句中显示说明.

SELECT rapnet_diamonds.diamond_id, rapnet_diamonds.carat,
    clarity_lookup.clarity, rapnet_diamonds.color, cut_lookup.cut
FROM rapnet_diamonds
LEFT OUTER JOIN clarity_lookup ON rapnet_diamonds.clarity_score = clarity_lookup.clarity_score
LEFT OUTER JOIN cut_lookup ON rapnet_diamonds.cut_score = cut_lookup.cut_score
WHERE rapnet_diamonds.shape IN ('round','princess','oval') 
    AND (rapnet_diamonds.carat BETWEEN .1 AND 5) 
    AND (rapnet_diamonds.color BETWEEN 'D' AND 'Z') 
    AND (rapnet_diamonds.clarity_score BETWEEN 0 AND 10) 
    AND (rapnet_diamonds.cut_score BETWEEN 0 AND 5)