Magento2

use this query to see  all products that do not have images in magento2

SELECT sku FROM `catalog_product_entity` WHERE `entity_id` not in (SELECT `entity_id` FROM `catalog_product_entity_media_gallery_value` )

ignoring the "Not Visible Individually" products

you have to add this code to the block or to the page

 {{block class="Magento\Framework\View\Element\Template"  template="{Vendor}_{Module}::pages/example.phtml"}}

Example 

{{block class="Magento\Catalog\Block\Product\ListProduct" category_id="50" name="home.products.list.custom" template="Magento_Catalog::product/list.phtml"}} 

{{widget type="Magento\Catalog\Block\Category\Widget\Link" anchor_text="MY Custom category" title="Custom Category" template="category/widget/link/link_block.phtml" id_path="category/12"}}

there are three templates

Magento profiler can help you with the store performance tuning before the store release or during the exploitation.
The old UI for enabling/disabling the profiler is not available in Magento 2 and the profiler is disabled by default.
To enable one of the profiler formats mentioned above, you can edit .htaccess (a configuration file for Apache Web Server software):

    Choose one of the next expressions:

Most of us wanted or liked to change the Maintenance Page content, but it had difficulties doing that, now we will show you how easy is that can be

From the Magento root directory, switch to production mode:

 bin/magento deploy:mode:set production

Enable JavaScript bundling:

 bin/magento config:set dev/js/enable_js_bundling 1

Optimize bundling by minifying JavaScript files:

 bin/magento config:set dev/js/minify_files 1

Enable cache busting on static file URLs. This ensures users get the latest version of the assets anytime they update:

in case we want to change this configuration

«Stores» → «Configuration» 3 → «Advanced» → «Developer» → «Static Files Settings» → «Sign Static Files»

we can execute this query

disable

The easiest way to make the tax/vat id mandatory in the checkout page is to change the is_required in the eav_attribute table

you can use this Query to change the value from 0 => 1

UPDATE `eav_attribute` SET `is_required` = '1' WHERE `eav_attribute`.`attribute_code` = 'vat_id';

or you can use this code when you want to use a custom extesnion

$installer->updateAttribute('customer_address', 'vat_id', 'is_required', true);

in this wiki we will provide a simple form with Validation that we can use in Magento2, hope this will be helpful for all readers

you can use the below code in phtml file

To add a new comment to existing order and change the order status you can use this endpoint

/rest/V1/orders/{order_id}/comments

and the json data is

{
    "statusHistory": {
        "comment": "Your Comment Here",
        "created_at": "2018-06-05  15:22:04",
        "parent_id": {order_id},
        "is_customer_notified": 0,
        "is_visible_on_front": 1,
        "status": "pending"
    }
}