主鍵列不允許空值

Question

我有一個關於主鍵或複合鍵的問題。我創建了一個只有兩個屬性並且都是主鍵的表。

的主鍵的名稱是item_ID̀ and SName`

這兩個外鍵的另一個主鍵（對於其他兩個表），其中： item_ID --> ID和SName --> SkillName

 
ITEM ID  SName 

1  Basic weapons 
2 
3 
4  Heavy weapon 
5  Exotic Weapons 
6  Heavy weapon 
7  Power weapon 

和結果是這樣的：

身份證號碼2和3不需要技能名稱要求。出於這個原因，我已經這樣實現（因爲主鍵不允許爲空）：

INSERT INTO Requierments (item_ID, SName) VALUES ( 
01, 'Basic weapons'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
02, null); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
03, null); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
04, 'Heavy weapon'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
05, 'Exotic Weapons'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
06, 'Heavy weapon'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
07, 'Power weapon'); 

這是否正確完成？還是有另一種方式來編碼該ID不需要特定的SName？

---

這裏是在3代表的代碼：

CREATE TABLE `talents` (
    `SkillName` varchar(30) NOT NULL DEFAULT '', 
    `Bonus` varchar(30) DEFAULT NULL, 
    `Description` varchar(70) DEFAULT NULL, 
    `R_Str` int(11) DEFAULT NULL, 
    `R_WS` int(11) DEFAULT NULL, 
    `R_BS` int(11) DEFAULT NULL, 
    `R_Fel` int(11) DEFAULT NULL, 
    `R_Per` int(11) DEFAULT NULL, 
    `R_Int` int(11) DEFAULT NULL, 
    `R_Agi` int(11) DEFAULT NULL, 
    `R_WP` int(11) DEFAULT NULL, 
    `Talent_requiert` varchar(30) DEFAULT NULL, 
    PRIMARY KEY (`SkillName`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8; 

CREATE TABLE `requierments` (
    `item_ID` int(11) NOT NULL DEFAULT '0', 
    `SName` varchar(30) NOT NULL DEFAULT '', 
    PRIMARY KEY (`item_ID`,`SName`), 
    CONSTRAINT `requierments_ibfk_1` FOREIGN KEY (`item_ID`) REFERENCES `item` (`ID`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8; 


CREATE TABLE `item` (
    `ID` int(11) NOT NULL DEFAULT '0', 
    `Name_` varchar(30) DEFAULT NULL, 
    `Weight` int(11) DEFAULT NULL, 
    `Value_` int(11) DEFAULT NULL, 
    `Availability` varchar(30) DEFAULT NULL, 
    PRIMARY KEY (`ID`) 
) ENGINE=InnoDB DEFAULT CHARSET=utf8; 

的想法是在表中的要求ITEM_ID --->在項目表，並在人才SNAME ---> SkillName ID。出於某種原因，我能夠從item_ID到ID的外鍵，但不能從SName到技巧名稱：

我已經添加到這些表中的值如下（OBS，在表中我需要設置ID 2和3「」，因爲不需要任何天賦可以選擇它。但我不確定我是否允許使用該方法？

INSERT INTO Talents (SkillName, Bonus, Description, R_Str, R_WS, R_BS, R_Fel, R_Per, R_Int, R_Agi, R_WP, Talent_requiert) VALUES (
'ambidextrous', 0, 'use either hand equally well', 0, 0, 0, 0, 0, 0, 30, 0, null); 

INSERT INTO Talents (SkillName, Bonus, Description, R_Str, R_WS, R_BS, R_Fel, R_Per, R_Int, R_Agi, R_WP, Talent_requiert) VALUES (
'Frenzy', 0, 'enter psychotic rage to gain combat bonus', 0, 0, 0, 0, 0, 0, 0, 0, null); 

INSERT INTO Talents (SkillName, Bonus, Description, R_Str, R_WS, R_BS, R_Fel, R_Per, R_Int, R_Agi, R_WP, Talent_requiert) VALUES (
'battle rage', 0, 'parry while frenzied', 0, 0, 0, 0, 0, 0, 0, 0, 'Frenzy'); 

INSERT INTO Talents (SkillName, Bonus, Description, R_Str, R_WS, R_BS, R_Fel, R_Per, R_Int, R_Agi, R_WP, Talent_requiert) VALUES (
'Exotic Weapons', 0, 'Player is able to use exotic weapons', 0, 0, 0, 0, 0, 0, 0, 0, 'Basic weapons'); 

INSERT INTO Talents (SkillName, Bonus, Description, R_Str, R_WS, R_BS, R_Fel, R_Per, R_Int, R_Agi, R_WP, Talent_requiert) VALUES (
'Basic weapons', 0, 'Player is able to use Basic weapons', 0, 0, 0, 0, 0, 0, 0, 0, null); 

INSERT INTO Talents (SkillName, Bonus, Description, R_Str, R_WS, R_BS, R_Fel, R_Per, R_Int, R_Agi, R_WP, Talent_requiert) VALUES (
'Heavy weapon', 0, 'Player is able to use heavy weapons', 30, 0, 0, 0, 0, 0, 0, 0, null); 

INSERT INTO Talents (SkillName, Bonus, Description, R_Str, R_WS, R_BS, R_Fel, R_Per, R_Int, R_Agi, R_WP, Talent_requiert) VALUES (
'Power weapon', 0, 'Player is able to use power weapons ', 40, 30, 0, 0, 0, 0, 0, 0, null); 



INSERT INTO Item (ID, Name_, Weight, Value_, Availability) VALUES (
01, 'Las Carbine', 3, 75, 'Common'); 

INSERT INTO Item (ID, Name_, Weight, Value_, Availability) VALUES (
02, 'Laspistol', 1, 50, 'Common'); 

INSERT INTO Item (ID, Name_, Weight, Value_, Availability) VALUES (
03, 'Shotgun', 5, 60, 'average'); 

INSERT INTO Item (ID, Name_, Weight, Value_, Availability) VALUES (
04, 'Heavy Bolter', 40, 2000, 'Very Rare'); 

INSERT INTO Item (ID, Name_, Weight, Value_, Availability) VALUES (
05, 'Needle pistol', 2, 1250, 'Very Rare'); 

INSERT INTO Item (ID, Name_, Weight, Value_, Availability) VALUES (
06, 'Chainsword', 6, 275, 'Rare'); 

INSERT INTO Item (ID, Name_, Weight, Value_, Availability) VALUES (
07, 'Power Sword', 4, 2500, 'Very Rare'); 


INSERT INTO Requierments (item_ID, SName) VALUES ( 
01, 'Basic weapons'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
02, ''); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
03, ''); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
04, 'Heavy weapon'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
05, 'Exotic Weapons'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
06, 'Heavy weapon'); 

INSERT INTO Requierments (item_ID, SName) VALUES ( 
07, 'Power weapon'); 

Answer 1

您正在嘗試處理情況的Item有沒有Requirement換句話說，這樣一個Item有沒有關係有一個Talent：根本不要在中插入任何東西爲此Item！