CODEWITHSUNDEEP
sqlmysqldatabasesqlitenull
huy
huy

Reputation: 1914

Why can I add null value to primary key in SQLite?

I have this code, you can try on db-fiddle:

CREATE TABLE EMPLOYEE
( ID        INT,
  Name      VARCHAR(15) NOT NULL,
  Age       INT,
  Dnumber   INT,
  Level     INT,
  PRIMARY KEY (ID)
);

INSERT INTO EMPLOYEE (ID, Name, Age, Dnumber, Level) VALUES(1,'Tom', 21, 2, 5);
INSERT INTO EMPLOYEE (ID, Name, Age, Dnumber, Level) VALUES(2,'Lucky', 22, 2, 3);
INSERT INTO EMPLOYEE (ID, Name, Age, Dnumber, Level) VALUES(NULL,'Blue', 22, 2, 3);

If I use SQLite, I can add the NULL value but it cannot if I use MySQL. I will get this error:

Schema Error: Error: ER_BAD_NULL_ERROR: Column 'ID' cannot be null

What is the reason why I can add it to SQLite?

Upvotes: 12

Views: 5533

Answers (4)

Super Kai - Kazuya Ito
Super Kai - Kazuya Ito

Reputation: 1

In SQLite basically, you can add NULL to PRIMARY KEY columns but you cannot add NULL to INTEGER PRIMARY KEY and INTEGER PRIMARY KEY AUTOINCREMENT columns even if they don't have NOT NULL constraint. My answer explains it more.

Upvotes: 2

huy
huy

Reputation: 1914

Thanks to @astentx for the advice. I checked the documentation and it said that:

According to the SQL standard, PRIMARY KEY should always imply NOT NULL. Unfortunately, due to a bug in some early versions, this is not the case in SQLite. Unless the column is an INTEGER PRIMARY KEY or the table is a WITHOUT ROWID table or the column is declared NOT NULL, SQLite allows NULL values in a PRIMARY KEY column. SQLite could be fixed to conform to the standard, but doing so might break legacy applications. Hence, it has been decided to merely document the fact that SQLite allowing NULLs in most PRIMARY KEY columns.

Upvotes: 19

Rahul Patel
Rahul Patel

Reputation: 639

ID field is the primary key(a primary index exists on the field), that is why the field cannot accept the null values. It should have not null unique values.

Official Doc:

https://dev.mysql.com/doc/refman/8.0/en/constraint-primary-key.html

Upvotes: -3

thommyberglund
thommyberglund

Reputation: 104

PRIMARY KEY (ID) isn't allowed to store NULL for MySQL, if i remember correctly. So your ID column can't store NULL values.

Upvotes: -2

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