Adding a column with a default value in MySQL is a straightforward process that can be achieved using various methods. In this article, we will explore different ways to add a new column and set its default value.

One of the most common methods is to use the `ALTER TABLE` statement. This method allows you to modify an existing table by adding a new column with a default value. For example, the following command adds a new column named `newColumn` with a default value of 'test':

```sql

ALTER TABLE tableName ADD newColumn varchar(20) DEFAULT 'test';

```

However, if you are trying to add a column with a default value that is not a constant, such as `CURRENT_TIMESTAMP`, you will encounter a syntax error. In this case, you can use the `TIMESTAMP` data type instead of `DATETIME`. For example:

```sql

CREATE TABLE test (str varchar(32), ts TIMESTAMP DEFAULT CURRENT_TIMESTAMP);

```

In MySQL 5.6.5 and later versions, you can also add a default value to a `DATETIME` field using the same syntax as above.

Another way to add a column with a default value is by using the `INSERT INTO` statement when inserting data into the table. For example:

```sql

INSERT INTO test (str) VALUES ('demo');

```

However, this method has its limitations. If you are trying to set a default value for all rows in the table, this method may not be suitable.

In addition, Sequelize, a popular ORM library, also provides an easy way to add a column with a default value when defining a model. For example:

```javascript

const sequelize = new Sequelize('database', 'username', 'password');

const User = sequelize.define('User', {

name: {

type: DataTypes.STRING,

allowNull: false,

defaultValue: 'default value'

}

});

```

In this example, the `name` column is defined with a default value of `'default value'`.

In conclusion, adding a column with a default value in MySQL can be achieved using various methods. Whether you are trying to add a constant or dynamic default value, there is always a way to achieve your goal. By understanding the different methods available, you can choose the one that best suits your needs.

Mysql add column with default value