set primary key mySQL code example
Example 1: mysql change primary key
ALTER TABLE tableName MODIFY COLUMN id INT;
ALTER TABLE tableName DROP PRIMARY KEY;
ALTER TABLE tableName ADD PRIMARY KEY (new_id);
ALTER TABLE tableName MODIFY COLUMN new_id INT AUTO_INCREMENT;
Example 2: what is primary key
Primary Key :
It is unique column in every table in a database
It can ONLY accept;
- nonduplicate values
- cannot be NULL
Foreign Key:
It is a column that comes from a different table and
using Foreign key tables are related each other
It is the primary key of another table
It can be duplicate or null for another table
Unique Key:
Only unique value and also can contain NULL
Example 3: MySQL Primary Key
Typically, you define the primary key for a table in the CREATE TABLE statement.
If the primary key has one column, you can use the PRIMARY KEY constraint as a column constraint:
CREATE TABLE table_name(
primary_key_column datatype PRIMARY KEY,
...
);