database - 如何从另一个表继承列值

Question

我正在尝试创建一个表，其中包含应该从另一个表继承值的列，但问题是这些值不是唯一的(不是另一个表的主键)。我怎样才能做到这一点？

我试图将其设置为外键，但无法完成，因为该值不是主键。

我想要从另一个表 (tblPartsServices) 继承的表 tblOrderCharges 中的 fldDiscountPercent 和 fldChargeType。我将如何实现这一目标？

CREATE TABLE tblPartsServices(
    fldPartServiceId        VARCHAR2(10) NOT NULL,
    fldPartServiceDescription           VARCHAR2(255),
    fldPartServiceType  CHAR(1)  NOT NULL,          -- P for Part, S for Service, O for Other
    fldPartServiceAmount    NUMBER(8,2) NOT NULL,
    fldDiscountPercent NUMBER(2) ,
    fldStatus CHAR(1) NOT NULL,             -- A for Active, I for Inactive
    CONSTRAINT PartService_pk PRIMARY KEY (fldPartServiceId)
);

CREATE TABLE tblOrderCharges(
    fldChargeId NUMBER(10) NOT NULL,
    fldChargeReference VARCHAR2(10) NOT NULL,    --  Part number or service number (Could be inherited from PartsServices table)
    fldChargeCode VARCHAR2(10) ,            --  Part number or service number (Could be inherited from PartsServices table)
    fldChargeType CHAR(1),                                   --  Type: P for Part, S for Service, O for Other (Could be inherited from PartsServices table)
    fldChargeAmount NUMBER(18, 2) ,                 --  Part or Service Amount (Could be inherited from PartsServices table)
    fldDiscountPercent NUMBER(2),                    --  Part or Service Discount (Could be inherited from PartsServices table)
    fldRemarks VARCHAR2(40),
    fldStatus CHAR(1) NOT NULL,                                 --  A for Active, I for Inactive
    fldOrderId VARCHAR2(10) NOT NULL,
    fldTechnicianId VARCHAR2(10),           -- Null if no technician has been assigned
    CONSTRAINT Charge_pk PRIMARY KEY (fldChargeId),
    CONSTRAINT fk_Order FOREIGN KEY (fldOrderId) REFERENCES tblJobOrders(fldOrderId),
    CONSTRAINT fk_Technician FOREIGN KEY (fldTechnicianId) REFERENCES tblTechnicians(fldTechnicianId),
    CONSTRAINT fk_ChargeReference FOREIGN KEY (fldChargeReference) REFERENCES tblPartsServices(fldPartServiceId),
    CONSTRAINT fk_ChargeCode FOREIGN KEY (fldChargeCode) REFERENCES tblPartsServices(fldPartServiceId),
    CONSTRAINT fk_ChargeType FOREIGN KEY (fldChargeType) REFERENCES tblPartsServices(fldPartServiceType),
    CONSTRAINT fk_DiscountPercent FOREIGN KEY (fldDiscountPercent) REFERENCES tblPartsServices(fldDiscountPercent)
);

Answer 1

如您所见，外键是指向另一个表的主键的链接。 This website可以帮助理解这个概念。

您可能需要考虑向表 tblOrderCharges 添加一个触发器，该触发器从其他表中选择必要的列并将选定的值放入 tblOrderCharges 中。您可以指定用于处理返回的非唯一值的过滤条件。会是这样的:

create or replace trigger myexampletrigger
before insert or update
on tblOrderCharges
for each row
DECLARE
// your variables here
BEGIN
  select fldDiscountPercent,fldPartServiceType into YourVariable1,YourVariable2 from tblPartsServices where /*your criteria here*/;

  :new.fldDiscountPercent := YourVariable1;
  :new.fldChargeType := YourVariable2;
END;
/