So fügen Sie in SQL keine Nullbeschränkung hinzu
ALTER TABLE table_name MODIFY column_name datatype NOT NULL;
Enthusiastic Echidna
ALTER TABLE table_name MODIFY column_name datatype NOT NULL;
By default, a column can hold NULL values.
The NOT NULL constraint enforces a column to NOT accept NULL values.
This enforces a field to always contain a value, which means that you cannot insert a new record, or update a record without adding a value to this field.
Sql NOT NULL in creating a table
CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255) NOT NULL,
Age int
);CREATE TABLE Colleges (
college_id INT NOT NULL,
college_code VARCHAR(20),
college_name VARCHAR(50)
);CREATE TABLE Colleges (
college_id INT NOT NULL,
college_code VARCHAR(20) NOT NULL,
college_name VARCHAR(50)
);CREATE TABLE Persons (
ID int NOT NULL,
LastName varchar(255) NOT NULL,
FirstName varchar(255) NOT NULL,
Age int
);