我正在使用PostgreSQL数据库和Node.js内置的Web应用程序。
我有一张表cases，就像那样：
disease | country | year | number | rate
------------+---------------------------------------+------+-----------+--------
Diphtheria | Austria | 1989 | 190.00 | 2.47
Tetanus | Austria | 1989 | NaN | NaN
Pertussis | Austria | 1989 | 0.00 | 0.00
Measles | Austria | 1989 | NaN | NaN
Mumps | Austria | 1989 | 0.00 | 0.00
Rubella | Austria | 1989 | NaN | NaN
Polio | Austria | 1989 | NaN | NaN
Diphtheria | Belgium | 1989 | 180.00 | 2.42
Tetanus | Belgium | 1989 | 5.00 | 0.04
Pertussis | Belgium | 1989 | 1.00 | 0.01
Measles | Belgium | 1989 | 0.00 | 0.00
Mumps | Belgium | 1989 | 2052.00 | 50.00
Rubella | Belgium | 1989 | 0.00 | 0.00
Polio | Belgium | 1989 | NaN | NaN
Diphtheria | Austria | 1990 | 5.00 | 0.01
Tetanus | Austria | 1990 | 152.00 | 2.41
Pertussis | Austria | 1990 | 0.00 | 0.00
Measles | Austria | 1990 | 850.00 | 3.55
Mumps | Austria | 1990 | NaN | NaN
Rubella | Austria | 1990 | 55.00 | 3.00
Polio | Austria | 1990 | 0.00 | 0.00
Diphtheria | Belgium | 1990 | 191.00 | 2.48
Tetanus | Belgium | 1990 | 20.00 | 2.00
Pertussis | Belgium | 1990 | 5.00 | 0.40
Measles | Belgium | 1990 | 0.00 | 0.00
Mumps | Belgium | 1990 | 0.40 | 0.02
Rubella | Belgium | 1990 | 85.00 | 6.08
Polio | Belgium | 1990 | 10.00 | 0.60
... | ... | ... | ... | ...
总共有8040行，7种不同的疾病值，32种不同的国家值和36种不同的年份值。
我必须根据疾病结合一些值并找到最大值。 例如，我需要将Diphtheria，Tetanus和Pertussis组合成一个新值（称为DTP），其数量（和速率）是单个值的总和。 麻疹，腮腺炎和风疹成为MMR也是如此。 其他值（脊髓灰质炎）仍然保持原样。
所以，这是中间步骤：
disease | country | year | number | rate
------------+---------------------------------------+------+-----------+--------
DTP | Austria | 1989 | 190.00 | 2.47
MMR | Austria | 1989 | 0.00 | 0.00
Polio | Austria | 1989 | NaN | NaN
DTP | Belgium | 1989 | 186.00 | 2.47
MMR | Belgium | 1989 | 2052.00 | 50.00
Polio | Belgium | 1989 | NaN | NaN
DTP | Austria | 1990 | 157.00 | 2.42
MMR | Austria | 1990 | 905.00 | 6.55
Polio | Austria | 1990 | 0.00 | 0.00
DTP | Belgium | 1990 | 216.00 | 4.88
MMR | Belgium | 1990 | 85.40 | 7.00
Polio | Belgium | 1990 | 10.00 | 0.60
... | ... | ... | ... | ...
汇总值，我认为NaN为0。
之后我需要为每个不同的疾病元素设置最大值，所以：
max DTP number = 216.00
max DTP rate = 4.88
max MMR number = 2052.00
max MMR rate = 5.00
max Polio number = 10.00
max Polio rate = 0.60
我需要的是最大值，所以我不介意创建中间表。它既可以创造，也可以不创造。
我该怎么办？
答案 0 :(得分：2)
你可以用这个：
WITH intermediate_table AS
(
SELECT
SUM(CASE WHEN disease IN ('Diphtheria', 'Tetanus', 'Pertussis') AND number <> 'NaN' THEN number END) AS DTP_NUMBER,
SUM(CASE WHEN disease IN ('Diphtheria', 'Tetanus', 'Pertussis') AND rate <> 'NaN' THEN rate END) AS DTP_RATE,
SUM(CASE WHEN disease IN ('Measles', 'Mumps', 'Rubella') AND number <> 'NaN' THEN number END) AS MMR_NUMBER,
SUM(CASE WHEN disease IN ('Measles', 'Mumps', 'Rubella') AND rate <> 'NaN' THEN rate END) AS MMR_RATE,
SUM(CASE WHEN disease IN ('Polio') AND number <> 'NaN' THEN number END) AS Polio_NUMBER,
SUM(CASE WHEN disease IN ('Polio') AND rate <> 'NaN' THEN rate END) AS Polio_RATE,
country,
year
FROM cases
GROUP BY country, year
)
SELECT MAX(DTP_NUMBER) AS MAX_DTP_NUMBER,
MAX(DTP_RATE) AS MAX_DTP_RATE,
MAX(MMR_NUMBER) AS MAX_MMR_NUMBER,
MAX(MMR_RATE) AS MAX_MMR_RATE,
MAX(Polio_NUMBER) AS MAX_Polio_NUMBER,
MAX(Polio_RATE) AS MAX_Polio_RATE
FROM intermediate_table;
如果您的查询需要，请使用ROUND。