yii\db\ColumnSchemaBuilder::buildUniqueString PHP Method

Builds the unique constraint for the column.

protected buildUniqueString ( ) : string
return	string	returns string 'UNIQUE' if [[isUnique]] is true, otherwise it returns an empty string.

    protected function buildUniqueString()
    {
        return $this->isUnique ? ' UNIQUE' : '';
    }

ColumnSchemaBuilder