使用COUNT的SELECT语句

Question

CREATE TABLE hardware 
(
name  varchar(10), 
ID  serial    PRIMARY KEY NOT NULL 
); 

CREATE TABLE games 
(
name  varchar(100), 
ID  serial     PRIMARY KEY 
); 

CREATE TABLE gameVersion 
(
gameID  integer   REFERENCES games(ID), 
version  integer, 
ID  char(10)  PRIMARY KEY  NOT NULL 
); 

CREATE TABLE versionHardware 
(
hardwareID  integer   REFERENCES hardware(ID), 
versionID  char(10)  REFERENCES gameVersion(ID), 
ID  serial   PRIMARY KEY 
); 

CREATE TABLE cheatCodes 
(
ID  serial   PRIMARY KEY  NOT NULL, 
code  varchar(60), 
gameID  integer   REFERENCES games(ID) 
); 

我如何找到任何可以使用ID为（5）的硬件进行游戏的记录上的cheatCodes数量。

我试图

SELECT COUNT(*) 
    FROM cheatCodes, games, gameVersion,hardware, versionHardware 
    WHERE cheatCodes.GameId = games.ID 
    AND gameVersion.gameID = games.ID 
    AND versionHardware.versionID = gameVersion.ID 
    AND hardware.ID = 5; 

但它不给我正确的答案。

Answer 1

尝试：

SELECT COUNT(DISTINCT cheatCodes.GameId) as CheatCodeCount 
FROM cheatCodes, games, gameVersion,hardware, versionHardware 
WHERE cheatCodes.GameId = games.ID 
AND gameVersion.gameID = games.ID 
AND versionHardware.versionID = gameVersion.ID 
AND versionHardware.hardwareID = hardware.id 
AND hardware.ID = 5; 

Answer 2

请尝试下面的查询。硬件表的链接丢失， 链接。

SELECT COUNT(*) 
    FROM cheatCodes, games, gameVersion,hardware, versionHardware 
    WHERE cheatCodes.GameId = games.ID 
    AND gameVersion.gameID = games.ID 
    AND versionHardware.versionID = gameVersion.ID 
    AND hardware.id = versionHardware.hardwareID  
    AND hardware.ID = 5;