How to find the base table of view? A view is just an SQL query on a table - in the UI how can I find what table an existing view is based on?
Not exactly. But, you may find it helpful to goto Views -&gt; Settings -&gt; Advanced Settings from admin/structure/views and check the Show SQL Query in your View Preview.

Then goto a view and generate a preview and you will see the SQL statement Drupal is using to generate a query. Some parts of the Views lifecycle to render a views display though are fulfilled by PHP and not SQL. For example drupal Fields are inserted into each row of the the resultset if your display mode is either Fields or Rendered Entity. By this I mean the raw SQL does not perform a JOIN upon every field_data_* table used by your content type -- this is handled in PHP, and not SQL. All of this is also dependent on the Storage mechanism being used by Drupal (the default is SQL, but other backends exist such as NoSQL backends).

I'm just saying the SQL preview will show you ~70% of what Drupal is doing to generate your view. But there is some behind the scenes processing with sql metadata and hook processing going on too.