Get Auto Increment Field from a table using Magento 2.

You can get the Auto Increment Field from a database table using Magento 2 as Best coding practice way.

You need to use getAutoIncrementField() for getting the auto-increment field from the table.

Output: Returns field name if an auto-increment field is available otherwise return as false.

<?php
namespace Path\To\Class;

use Magento\Framework\App\ResourceConnection;

class AutoIncrementField {

    const ORDER_TABLE = 'sales_order';

    /**
     * @var ResourceConnection
     */
    private $resourceConnection;

    public function __construct(
       ResourceConnection $resourceConnection
    ) {
       $this->resourceConnection = $resourceConnection;
    }

    /**
    * get AutoIncremntFieldName using Query
    *
    * @return string|bool
    */
    public function getAutoIncremntFieldName()
    {
      $connection  = $this->resourceConnection->getConnection();
      $tableName = $connection->getTableName(self::ORDER_TABLE);
      $getFieldName = $connection->getAutoIncrementField($tableName);

      return $getFieldName;
    }
}

You can call $this->getAutoIncremntFieldName() function to check sales_order table with auto_increment field name.

Output:
entity_id