在 SQL 中，如何在滿足另一個條件時為屬性值設定限制？例如，學生最多可以借用 3 個資源，員工最多可以借用 6 個資源
Create Table USER_T
( UserID int PRIMARY KEY NOT NULL,
UserType varchar (25) NOT NULL,
No_of_Resources_Borrowed int check (No_of_Resources_Borrowed=<6)
CONSTRAINT con_user_typ check (UserType IN ('Student','Staff'))
);
uj5u.com熱心網友回復：
你想要一個 CONSTRAINT 子句
Create Table USER_T
( UserID int PRIMARY KEY NOT NULL,
UserType varchar (25) NOT NULL,
No_of_Resources_Borrowed int NOT NULL,
CONSTRAINT Resources_by_type CHECK (
No_of_Resources_Borrowed
<= case UserType when 'Student' then 3 when 'Staff' then 6 else 2147483647 end ),
CONSTRAINT con_user_typ CHECK (UserType IN ('Student','Staff'))
);
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