在 Oracle SQL 中使用复杂 IF 语句

您好，我正在尝试在 Band 属性中编写 If 语句，但没有成功 T_T。我想做的是根据所有者类别、棚屋和供水属性设置单个角色 A、B、C、D。任何帮助都会很棒^^。

CREATE TABLE Rent_Band
(
    Plot_ID NUMBER(3),
    Band VARCHAR(1)
    IF SELECT * FROM Rent_Band WHERE Owner_Category = 'Council' AND WHERE Sheds ='No' THEN Band ='A'
    ELSE IF SELECT * FROM Rent_Band WHERE Owner_Category = 'Private' AND WHERE  Water_Supply ='Yes' THEN Band ='D'
    ELSE IF SELECT * FROM Rent_Band WHERE Owner_Category = 'Council' AND WHERE  Water_Supply ='No' AND WHERE Sheds ='Yes' THEN Band ='B'
    ELSE IF SELECT * FROM Rent_Band WHERE Owner_Category = 'Private' AND WHERE Water_Supply ='No' AND WHERE Sheds ='No' THEN Band ='B'
    ELSE THEN Band = 'C',
    Rent_Charge NUMBER(4), 
    Owner_Category VARCHAR(10) CONSTRAINT Checking_Owner_Category CHECK((Owner_Category='Private') OR (Owner_Category='Council')), 
    Sheds VARCHAR(3) CHECK((Sheds='Yes') OR (Sheds='No')), 
    Water_Supply VARCHAR(3) CHECK((Water_Supply='Yes') OR (Water_Supply='No'))
)

Read 文档在虚拟列上：

CREATE TABLE Rent_Band
(
    Plot_ID NUMBER(3),
    Band VARCHAR(1) AS
       (CASE WHEN Owner_Category = 'Council' AND Sheds ='No' THEN 'A'
            WHEN Owner_Category = 'Private' AND Water_Supply ='Yes' THEN 'D'
            WHEN Owner_Category = 'Council' AND Water_Supply ='No' AND Sheds ='Yes' THEN 'B'
            WHEN Owner_Category = 'Private' AND Water_Supply ='No' AND Sheds ='No' THEN 'B'
       ELSE 'C' END),
    Rent_Charge NUMBER(4), 
    Owner_Category VARCHAR(10) CONSTRAINT Checking_Owner_Category CHECK((Owner_Category='Private') OR (Owner_Category='Council')), 
    Sheds VARCHAR(3) CHECK((Sheds='Yes') OR (Sheds='No')), 
    Water_Supply VARCHAR(3) CHECK((Water_Supply='Yes') OR (Water_Supply='No'))
)

顺便说一句，我强烈推荐：

• using a bit字段而不是Yes/No约束为Sheds and Water_Supply（节省空间和开销检查约束，并在大多数应用程序语言中直接转换为布尔值）
• 使用查找表Owner_Category出于基本相同的原因而不是字符串约束