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Should we break One to Many Relation which is unidirectional into a JoinTable
First-time database design: am I overengineering?Database normization 2nd form: does field should depend on FK also?query left join or data insert?SQL Inner Join Two Tables supplying both sets of dataDatabase 1…n relation with several owner tablesreplacing Duplicate rows in a table and in tables having foreign key reference to the 1st tableProvide name of an attribute rather than the IDHibernate One-To-Many Mapping issue using @JoinTable
I am currently working on an application where I have 2 Tables. User and Team. User has UserId as PK and UserPassword.
Team table has TeamId as PK and TeamName.
Originally I had one single table where I had UserId, UserPassword and TeamId but it was pointed out to me that the current design is not normalized. Hence I had to break the table into User, Team and also a Join Table named User_Team which contains UserId as PK from User table and TeamId as PK from Team table.
Constraints
One User can be in only 1 team and 1 team can have many users.
So as per my understanding, it is a OneToMany from Team to User side.
I have made UserId and TeamId together as a composite key and also made it unique in the JoinTable(User_Team) so that 1 user cannot be in multiple teams.
My query is that is it necessary to break the table into Team table seperately. Cant I just have all 3 fields in one single table. Can someone explain me how it is not normalized. Also let me know if there is a need of JoinTable in this case.
sql database hibernate database-design database-diagram
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
add a comment |
I am currently working on an application where I have 2 Tables. User and Team. User has UserId as PK and UserPassword.
Team table has TeamId as PK and TeamName.
Originally I had one single table where I had UserId, UserPassword and TeamId but it was pointed out to me that the current design is not normalized. Hence I had to break the table into User, Team and also a Join Table named User_Team which contains UserId as PK from User table and TeamId as PK from Team table.
Constraints
One User can be in only 1 team and 1 team can have many users.
So as per my understanding, it is a OneToMany from Team to User side.
I have made UserId and TeamId together as a composite key and also made it unique in the JoinTable(User_Team) so that 1 user cannot be in multiple teams.
My query is that is it necessary to break the table into Team table seperately. Cant I just have all 3 fields in one single table. Can someone explain me how it is not normalized. Also let me know if there is a need of JoinTable in this case.
sql database hibernate database-design database-diagram
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
1
If UserId is required to be unique then it is a key and (UserId,TeamId) cannot also be a key because it is not minimal (irreducible). TeamId→TeamName would be a non-key dependency resulting in an update anomaly. That's why having all three attributes in the same table would be a bad idea.
– nvogel
Mar 8 at 11:52
Could you be more informative by what you meant by minimal(irreducible) and also give me a scenario where update anomaly will arise.
– Kshitiz Bathwal
Mar 8 at 12:23
candidate key If you have the team name in a table where TeamId and TeamName are not keys then that is redundant information that has to be maintained on multiple rows. This is a data quality issue because the dependency between TeamId and TeamName is not enforced. There is the potential that the same TeamId could have multiple different names.
– nvogel
Mar 8 at 12:37
add a comment |
I am currently working on an application where I have 2 Tables. User and Team. User has UserId as PK and UserPassword.
Team table has TeamId as PK and TeamName.
Originally I had one single table where I had UserId, UserPassword and TeamId but it was pointed out to me that the current design is not normalized. Hence I had to break the table into User, Team and also a Join Table named User_Team which contains UserId as PK from User table and TeamId as PK from Team table.
Constraints
One User can be in only 1 team and 1 team can have many users.
So as per my understanding, it is a OneToMany from Team to User side.
I have made UserId and TeamId together as a composite key and also made it unique in the JoinTable(User_Team) so that 1 user cannot be in multiple teams.
My query is that is it necessary to break the table into Team table seperately. Cant I just have all 3 fields in one single table. Can someone explain me how it is not normalized. Also let me know if there is a need of JoinTable in this case.
sql database hibernate database-design database-diagram
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
I am currently working on an application where I have 2 Tables. User and Team. User has UserId as PK and UserPassword.
Team table has TeamId as PK and TeamName.
Originally I had one single table where I had UserId, UserPassword and TeamId but it was pointed out to me that the current design is not normalized. Hence I had to break the table into User, Team and also a Join Table named User_Team which contains UserId as PK from User table and TeamId as PK from Team table.
Constraints
One User can be in only 1 team and 1 team can have many users.
So as per my understanding, it is a OneToMany from Team to User side.
I have made UserId and TeamId together as a composite key and also made it unique in the JoinTable(User_Team) so that 1 user cannot be in multiple teams.
My query is that is it necessary to break the table into Team table seperately. Cant I just have all 3 fields in one single table. Can someone explain me how it is not normalized. Also let me know if there is a need of JoinTable in this case.
sql database hibernate database-design database-diagram
sql database hibernate database-design database-diagram
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
asked Mar 8 at 11:30
Kshitiz BathwalKshitiz Bathwal
338
338
1
If UserId is required to be unique then it is a key and (UserId,TeamId) cannot also be a key because it is not minimal (irreducible). TeamId→TeamName would be a non-key dependency resulting in an update anomaly. That's why having all three attributes in the same table would be a bad idea.
– nvogel
Mar 8 at 11:52
Could you be more informative by what you meant by minimal(irreducible) and also give me a scenario where update anomaly will arise.
– Kshitiz Bathwal
Mar 8 at 12:23
candidate key If you have the team name in a table where TeamId and TeamName are not keys then that is redundant information that has to be maintained on multiple rows. This is a data quality issue because the dependency between TeamId and TeamName is not enforced. There is the potential that the same TeamId could have multiple different names.
– nvogel
Mar 8 at 12:37
add a comment |
1
If UserId is required to be unique then it is a key and (UserId,TeamId) cannot also be a key because it is not minimal (irreducible). TeamId→TeamName would be a non-key dependency resulting in an update anomaly. That's why having all three attributes in the same table would be a bad idea.
– nvogel
Mar 8 at 11:52
Could you be more informative by what you meant by minimal(irreducible) and also give me a scenario where update anomaly will arise.
– Kshitiz Bathwal
Mar 8 at 12:23
candidate key If you have the team name in a table where TeamId and TeamName are not keys then that is redundant information that has to be maintained on multiple rows. This is a data quality issue because the dependency between TeamId and TeamName is not enforced. There is the potential that the same TeamId could have multiple different names.
– nvogel
Mar 8 at 12:37
1
1
If UserId is required to be unique then it is a key and (UserId,TeamId) cannot also be a key because it is not minimal (irreducible). TeamId→TeamName would be a non-key dependency resulting in an update anomaly. That's why having all three attributes in the same table would be a bad idea.
– nvogel
Mar 8 at 11:52
If UserId is required to be unique then it is a key and (UserId,TeamId) cannot also be a key because it is not minimal (irreducible). TeamId→TeamName would be a non-key dependency resulting in an update anomaly. That's why having all three attributes in the same table would be a bad idea.
– nvogel
Mar 8 at 11:52
Could you be more informative by what you meant by minimal(irreducible) and also give me a scenario where update anomaly will arise.
– Kshitiz Bathwal
Mar 8 at 12:23
Could you be more informative by what you meant by minimal(irreducible) and also give me a scenario where update anomaly will arise.
– Kshitiz Bathwal
Mar 8 at 12:23
candidate key If you have the team name in a table where TeamId and TeamName are not keys then that is redundant information that has to be maintained on multiple rows. This is a data quality issue because the dependency between TeamId and TeamName is not enforced. There is the potential that the same TeamId could have multiple different names.
– nvogel
Mar 8 at 12:37
candidate key If you have the team name in a table where TeamId and TeamName are not keys then that is redundant information that has to be maintained on multiple rows. This is a data quality issue because the dependency between TeamId and TeamName is not enforced. There is the potential that the same TeamId could have multiple different names.
– nvogel
Mar 8 at 12:37
add a comment |
1 Answer
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active
oldest
votes
No, you do not need a JoinTable for a OneToMany relation. Just have a teamId field on your User table and you're good to go.
As a rule of thumb:
OneToOne: Have a single table
OneToMany: Two tables, the "many" side (Userfor your case) has a foreign key
ManyToMany: Have a JoinTable
answered Mar 8 at 11:35
GBrandtGBrandt
54710
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No, you do not need a JoinTable for a OneToMany relation. Just have a teamId field on your User table and you're good to go.
As a rule of thumb:
OneToOne: Have a single table
OneToMany: Two tables, the "many" side (Userfor your case) has a foreign key
ManyToMany: Have a JoinTable
answered Mar 8 at 11:35
GBrandtGBrandt
54710
add a comment |
No, you do not need a JoinTable for a OneToMany relation. Just have a teamId field on your User table and you're good to go.
As a rule of thumb:
OneToOne: Have a single table
OneToMany: Two tables, the "many" side (Userfor your case) has a foreign key
ManyToMany: Have a JoinTable
answered Mar 8 at 11:35
GBrandtGBrandt
54710
add a comment |
No, you do not need a JoinTable for a OneToMany relation. Just have a teamId field on your User table and you're good to go.
As a rule of thumb:
OneToOne: Have a single table
OneToMany: Two tables, the "many" side (Userfor your case) has a foreign key
ManyToMany: Have a JoinTable
answered Mar 8 at 11:35
GBrandtGBrandt
54710
No, you do not need a JoinTable for a OneToMany relation. Just have a teamId field on your User table and you're good to go.
As a rule of thumb:
OneToOne: Have a single table
OneToMany: Two tables, the "many" side (Userfor your case) has a foreign key
ManyToMany: Have a JoinTable
answered Mar 8 at 11:35
GBrandtGBrandt
54710
answered Mar 8 at 11:35
GBrandtGBrandt
54710
answered Mar 8 at 11:35
GBrandtGBrandt
54710
answered Mar 8 at 11:35
GBrandtGBrandt
54710
54710
add a comment |
add a comment |
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If UserId is required to be unique then it is a key and (UserId,TeamId) cannot also be a key because it is not minimal (irreducible). TeamId→TeamName would be a non-key dependency resulting in an update anomaly. That's why having all three attributes in the same table would be a bad idea.
– nvogel
Mar 8 at 11:52
Could you be more informative by what you meant by minimal(irreducible) and also give me a scenario where update anomaly will arise.
– Kshitiz Bathwal
Mar 8 at 12:23
candidate key If you have the team name in a table where TeamId and TeamName are not keys then that is redundant information that has to be maintained on multiple rows. This is a data quality issue because the dependency between TeamId and TeamName is not enforced. There is the potential that the same TeamId could have multiple different names.
– nvogel
Mar 8 at 12:37