Feature: Add support for inserting multiple rows using a subquery

[kjohnson]

Related stellarwp/db#2

Description

This PR adds support for inserting the results on a query into another table using INSERT INTO.

Note: This does not support inserting multiple rows of known data (ie an array of data), rather this specifically supports using a subquery and a fluent syntax of chained methods. While support for insertMany() (or a similar feature) would also use INSERT INTO under the hood, the application logic is not covered by this implementation. Further, such a feature would more likely belong to the DB class rather than the QueryBuilder.

Affects

Adds a new insertInto() method to the CRUD trait of the QueryBuilder.

Visuals

DB::table('posts')

    // Subquery
    ->select(['ID', 'post_id'])
    ->selectRaw('(SELECT "postTitle") as meta_key')
    ->select(['post_title', 'meta_value'])

    // Insert Into
    ->insertInto('postmeta', ['post_id', 'meta_key', 'meta_value']);

INSERT INTO wp_postmeta (post_id, meta_key, meta_value)
    SELECT
        ID AS post_id,
        (SELECT "postTitle") as meta_key,
        post_title AS meta_value
    FROM wp_posts;

Testing Instructions

Pre-review Checklist

• Acceptance criteria satisfied and marked in related issue
• Relevant @unreleased tags included in DocBlocks
• Includes unit tests
• Self Review of code and UX completed

[JasonTheAdams]

Throwing in my 0.02, I was imagining a syntax such as:

DB::table('table1'
  ->select('a', 'b', 'c')
  ->where('a', '=', 'Kyle')
  ->insertColumns('col1', 'col2', 'col3')
  ->insertInto('talble2')

[kjohnson]

@JasonTheAdams I see what you were going for. When I did this first pass I was transcribing the INSERT INTO syntax to the Query Builder, but I'm reminded that a big benefit of the Query Builder is creating a syntax that better fits the application logic.

Ironic given my recent Slack post about this very benefit!

Goes to show how perspective can be a blind spot. As a writer I connected the path of least resistance.

[JasonTheAdams]

I'm going to close this as we'll re-open this in the https://github.com/stellarwp/db library after some syntax brainstorming. Let's link back to this, though, for reference!