如何在MySQL SELECT结果集中包含自定义计数？

Question

我有以下两个表：

TABLE: area
*City_ID   *Number   Name
--------   -------   ----
SUR        1         Fleetwood
SUR        2         Whalley
SUR        3         Guildford
SUR        4         Newton
SUR        5         Cloverdale
SUR        6         South Surrey
ABB        1         Abbotsford East
ABB        2         Abbotsford West
ABB        3         Aberdeen
ABB        4         Bradner
ABB        5         Central Abbotsford
ABB        6         Matsqui
ABB        7         Poplar
ABB        8         Sumas Mountain
ABB        9         Sumas Prairie

TABLE: city
*ID        Name
---        ----
SUR        Surrey
ABB        Abbotsford
LAN        Langley

使用以下声明：

SELECT DISTINCT area.City_ID, city.Name
FROM area
INNER JOIN city
WHERE area.City_ID = city.ID

我明白了：

SELECT:
City_ID    city.Name
-------    ---------
SUR        Surrey
ABB        Abbotsford

但是如何选择以下内容：

SELECT:
City_ID    city.Name    area_COUNT
-------    ---------    ----------
SUR        Surrey       6
ABB        Abbotsford   9

其中area_COUNT是area中每个对应City_ID的行数？

Answer 1

使用GROUP BY代替DISTINCT：

SELECT city.City_ID, city.Name, COUNT(*)
FROM area
INNER JOIN city
WHERE area.City_ID = city.ID
GROUP BY city.ID

Answer 2

您还应该在分组

中添加名称

SELECT area.City_ID, city.Name, count(*) as area_COUNT 
FROM area 
INNER JOIN city 
WHERE area.City_ID = city.ID 
GROUP BY area.City_ID,City.Name

Answer 3

在最后添加分组

SELECT area.City_ID, city.Name, count(*) as area_COUNT
FROM area
INNER JOIN city
WHERE area.City_ID = city.ID
GROUP BY area.City_ID

Answer 4

使用GROUP BY而不是DISTINCT：

SELECT city.City_ID，city.Name，COUNT（*） 从地区 INNER JOIN city WHERE area.City_ID = city.ID GROUP BY city.ID