Sql (Oracle)-- cannot insert value(could be the constraint factor) - sql

Question

As you can see in the code. three table have its own primary key. "protectmedalno" and "mastermedalno" are the foreign key of the player table.
protectmedalno could not be null. masterdealno could be null. I drop table protector first, then drop master , the last drop player.
There is weak relationship between table player and table master.
There is no problem with inserting the value of protector and master.
But inserting the value into table player, it will occur:
*Cause: A foreign key value has no matching primary key value.
*Action: Delete the foreign key or add a matching primary key.
I think that it is a problem with constraint.
insert into player values('01','Joe','101','');
insert into player values('02','Elsa','102','201');
insert into protector values('101','Dragon');
insert into protector values('102','Lion');
insert into master values('201','Fairy')
commits;
It could display the protector table and the master table.
But it could not show the player table.
drop table protector;
drop table master;
drop table player;
CREATE TABLE player (
playno NUMBER(2) NOT NULL,
playname VARCHAR2(30) NOT NULL,
protectmedalno CHAR(10) NOT NULL,
mastermedalno CHAR(10)
);
ALTER TABLE player ADD CONSTRAINT play_pk PRIMARY KEY ( playno );
CREATE TABLE protector (
protectmedalno CHAR(3) NOT NULL,
protectname VARCHAR2(30) NOT NULL
);
ALTER TABLE protector ADD CONSTRAINT protector_pk PRIMARY KEY ( protectmedalno );
CREATE TABLE master (
mastermedalno CHAR(3) NOT NULL,
mastername VARCHAR2(30) NOT NULL
);
ALTER TABLE master ADD CONSTRAINT master_pk PRIMARY KEY ( mastermedalno );
ALTER TABLE player
ADD CONSTRAINT player_protector_fk FOREIGN KEY ( protectmedalno )
REFERENCES protector ( protectmedalno );
ALTER TABLE player
ADD CONSTRAINT player_master_fk FOREIGN KEY ( mastermedalno )
REFERENCES master ( mastermedalno );

Answer 1

Since protector and master are the primary tables, you should populate the records there first. Then, insert into player and refer to those records:
insert into protector values('101','Dragon');
insert into protector values('102','Lion');
insert into master values('201','Fairy');
insert into player values('01','Joe','101','201'); -- refer to master
insert into player values('02','Elsa','102','201'); -- refer to master
Note that I edited the inserts into the player table such that both records refer to a record in the master table which actually exists.

Answer 2

You first have to insert protector and master, afterwards insert player since player refers to master and protector and values have to be inside there.
Do otherwise round on delete...
insert into protector values('101','Dragon');
insert into protector values('102','Lion');
insert into master values('201','Fairy');
insert into player values('01','Joe','101','');
insert into player values('02','Elsa','102','201');
If you delete first delete from player, then from protector and master.

Answer 3

To insert data in the player table, you need a record in the protector table. This is because of the foreign key restriction.
When inserting data in a table that has a foreign key(Which in this case of protector vs player, cannot be null), you have to create the foreign record first.
1. insert into protector values('101','Dragon');
2. insert into player values('01','Joe','101','');
3. insert into protector values('102','Lion');
4. insert into master values('201','Fairy');
5. insert into player values('02','Elsa','102','201');
commits;
I hope this helps, happy debugging :)

Answer 4

You are inserting in the wrong order: you must insert the master and protector first so that when you insert the player it can reference them:
insert into protector values('101','Dragon');
insert into protector values('102','Lion');
insert into master values('201','Fairy');
insert into player values('01','Joe','101',NULL);
insert into player values('02','Elsa','102','201');
Edit: '' is not NULL it's an empty String. To insert null use the explicit NULL jeyword.

Answer 5

Always include the columns when doing an insert. You should also use single quotes for only string and date constants.
insert into player(playno, playname, protectmedalno, mastermedalno)
values(1, 'Joe', '101', '');
I don't think the problem is specifically on player, but you should do this for all your inserts and you'll find the problem.

Answer 6

Populating the "parent" tables first (as our colleagues have suggested) is a step towards solving the problem. In order to get the foreign key constraint to work properly, I suggest modifying the DDL code, too.
With your tables in place (using Oracle 12c), we can do the following:
begin
insert into master ( mastermedalno, mastername ) values ('201','Fairy') ;
insert into protector ( protectmedalno, protectname )
values( '101', 'Dragon');
insert into protector ( protectmedalno, protectname )
values( '102', 'Lion');
end ;
/
SQL> select * from master;
MAS MASTERNAME
--- ------------------------------
201 Fairy
SQL> select * from protector ;
PRO PROTECTNAME
--- ------------------------------
101 Dragon
102 Lion
So far so good. When INSERTing into PLAYER, we get:
insert into player ( playno, playname, protectmedalno, mastermedalno )
values('02', 'Elsa', '102', '201');
-- ORA-02291: integrity constraint (...PLAYER_MASTER_FK) violated - parent key not found
Suggestion: use the same datatype for the foreign key and the referenced key. Just drop the PLAYER table (including its constraints), and create it afresh:
drop table player cascade constraints ;
CREATE TABLE player (
playno NUMBER(2) NOT NULL,
playname VARCHAR2(30) NOT NULL,
protectmedalno CHAR(3) NOT NULL, -- changed (was: CHAR(10))
mastermedalno CHAR(3) -- changed (was: CHAR(10))
);
ALTER TABLE player
ADD CONSTRAINT player_protector_fk FOREIGN KEY ( protectmedalno )
REFERENCES protector ( protectmedalno );
ALTER TABLE player
ADD CONSTRAINT player_master_fk FOREIGN KEY ( mastermedalno )
REFERENCES master ( mastermedalno );
Now execute the INSERTs.
begin
insert into player values('01','Joe','101',''); -- original INSERT
insert into player values('02','Elsa','102','201'); -- original INSERT
commit;
end;
/
-- PL/SQL procedure successfully completed.
The tables contain the following data now:
SQL> select * from player ;
PLAYNO PLAYNAME PROTECTMEDALNO MASTERMEDALNO
1 Joe 101 NULL
2 Elsa 102 201
SQL> select * from master ;
MASTERMEDALNO MASTERNAME
201 Fairy
SQL> select * from protector;
PROTECTMEDALNO PROTECTNAME
101 Dragon
102 Lion
Are both foreign key constraints working now? Yes.
SQL> insert into player values('03','Fifi','101','202');
Error starting at line : 1 in command -
insert into player values('03','Fifi','101','202')
Error report -
ORA-02291: integrity constraint (...PLAYER_MASTER_FK) violated - parent key not found
SQL> insert into player values('03','Fifi','103','201');
Error starting at line : 1 in command -
insert into player values('03','Fifi','103','201')
Error report -
ORA-02291: integrity constraint (...PLAYER_PROTECTOR_FK) violated - parent key not found