sql表创建中始终需要主键吗？

Question

I don't know if I created these tables in sql correctly. Can someone confirm I am doing this correctly or incorrectly? Can a table just have a foreign key or does it have to have a primary key? Thanks in advance.

CREATE TABLE Job(
JobId integer,
ToolName varchar(40),
status varchar(100),
start_time time,
finish_time time
PRIMARY KEY(JobId));

CREATE TABLE ErrorLog(
JobId integer,
ErrCode integer,
Description varchar(200),
PRIMARY KEY(ErrCode)
FOREIGN KEY(JobId) REFERENCES Job(JobId));

CREATE TABLE BLAST(
input varchar(100),
database varchar(100),
evalue varchar(100),
JobId integer, 
FOREIGN KEY (JobId) REFERENCES Job(JobId));

CREATE TABLE MitoLoc(
input varchar(100),
specificity varchar(100),
JobId integer,
FOREIGN KEY (JobId) REFERENCES Job(JobId));

Answer 1

It is best practice to create a primary key column on a table in a SQL RDBMS. Although SQL does not require tables to have primary keys.

Primary keys allow for a unique identifier to be set for each row in the table. This is the only way you can uniquely identify a specific row in the table, and the only way you'll be able to utilize a foreign key relationship.

Database servers, like SQL Server, also optimize both the storage and querying of tables better when they have primary keys defined.

Answer 2

Primary keys are a very good idea, but not required. Almost every table that I create has an automatically incremented primary key. This is in addition to several other columns that I keep around, such as CreatedAt and CreatedBy .

Foreign key relationships are typically to primary keys but can also be to unique keys.

Why do you want a primary key?

• So you can delete a row that is a duplicate, easily.
• So you can readily update a single row.
• An auto incremented primary key gives you an idea of the order that rows were inserted into the table.
• A single column primary key is much easier to handle with foreign key references.

There are, undoubtedly, other reasons. But those are a few.

As for your tables, I think Mitoch and Blast should have id columns that are primary keys. You can also declare other columns (or combinations) to be unique, if appropriate.

Answer 3

Not needed. But It is not good for table structure. you can create tables without primary key. and it can be have foreign key. But some DBMS don't allow to save table without primary key if you are not using primary key then

1. It is difficult to identify each record
2. Its record can't references to other tables

when creating table structure some time you have to create composite primary key that mean two or more columns together (combination ) can be primary key