Question

我有两个表：“系列”和“产品”

“系列”包含系列书籍的名称，“产品”包含各个书名的详细信息。

这样的事情：

Series Table:
id      series_name               series_description
1       Lord of the Rings         Trilogy of fantasy books recently made into film
2       A Song of Ice and Fire    Epic series of novels currently showing on HBO
3       Harry Potter              Famous Children's book series also loved by adults

Product Table:
id      product_name              series_id     author             etc...
1       Fellowship of the Ring    1             JRR Tolkien
2       The Two Towers            1             JRR Tolkien
3       Return of the King        1             JRR Tolkien
4       A Game of Thrones         2             George R R Martin
5       A Clash of Kings          2             George R R Martin
6       A Storm of Swords         2             George R R Martin
7       A Feast for Crows         2             George R R Martin
8       A Dance with Dragons      2             George R R Martin
9       Harry Potter and the...   3             JK Rowling
etc.

我想SELECT * FROM系列和COUNT（*）FROM产品，以便查询返回一个包含系列信息的表，数据库中与每个系列对应的产品数作为表的最后一列追加。我也想通过类型来做这个，所以在那里有一个额外的WHERE子句。如果选择“Fantasy and Magic”作为类型，它会看起来像这样：

id      series_name               series_description         number_of_products
1       Lord of the Rings         Trilogy of Fantasy...      3
2       A Song of Ice and Fire    Epic Series of Novels...   5
3       Harry Potter              Famous Children's book...  7

我想我可能需要一个LEFT JOIN，但到目前为止，我的最佳尝试仍然存在。

这是我到目前为止所做的，但我认为这可能是完全错误的。

SELECT  series.id,                                   
series.series_name,                                         
series.publisher_id,                                       
series.description, 
series.image, 
COUNT (product.*) as nRows 
FROM series 
LEFT OUTER JOIN product
ON series.id = product.series_id                    
WHERE series.genre = 'Fantasy and Magic'
GROUP BY ... (do I need a GROUP BY?)

任何帮助都会非常感激。提前谢谢！

Answer 1

几乎就在那里。试试这个。

SELECT  series.id,                                   
series.series_name,                                         
series.publisher_id,                                       
series.description, 
series.image, 
COUNT (product.id) as nRows 
FROM series 
LEFT OUTER JOIN product
ON series.id = product.series_id                    
WHERE series.genre = 'Fantasy and Magic'
GROUP BY series.id,                                   
series.series_name,                                         
series.publisher_id,                                       
series.description, 
series.image

Answer 2

不会this提供帮助;

select s.id, 
   s.series_name, 
   s.series_description, 
   (select count(*) from Products p where p.series_id = s.id) number_of_products 
from Series s

SELECT * FROM表A并计算表B中与特定字段匹配的相应行数

2 个答案: