MySQL Query Fetch Time increases when LEFT JOIN with big table

I am fetching the same amount of data with 2 different queries. However, one of them have a fetching time of ~x130 compared to the other. Being the only difference between the two queries a LEFT JOIN with a big table (4M rows).

Especifically, my problem goes like this:
I have table_a with 200K rows. table_b with 100 rows and table_c with 4M rows. The fields involved are indexed. table_a and table_c have a one to many cardinality.

My query looks something like this:

       SELECT         FROM           table_a a           LEFT JOIN table_b b ON = a.b_id           LEFT JOIN table_c c ON = b.c_id        GROUP BY; 

MySQL Workbench tells me that this query takes ~4s of Duration and 130 seconds of Fetch Time. However, when I remove the second LEFT JOIN with the big table, the query takes <1s of Duration and <1s Fetch Time.

I clearly understand why the query duration is increased. I am doing a kinda heavy left join. But, my question is: Why the fetching time is so much higher, if the fetched data is the same?

I have already increased innodb_buffer_pool_size with no success.

I am working in MySQL 8.0.19, with innodb as tables engine.

Is there something I am missing here? Thanks in advance for the help!

Removing the GROUP BY also improves the performance <1s of Duration and ~1s Fetch Time

How to fetch posts with offset in WordPress?

I have more than 100,000 posts and i fetch 20,000 posts in every page refresh, but now if i refresh the page i want to display new 20,000 posts rather than same.

Here is my Query

         $  args = array(             'post_type' => 'ebay_product',             'posts_per_page' => 20000,             'post_status' => array('publish'),             'orderby' => 'ID',             'order' => 'DESC'         ); 

Please help me to solve this issue. Any solution appreciated!

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Below is an example , where Blue is user input either entering/drop-down , Yellow is from the database that the user can pick from drop-down list and Green is automatically calculated by the system . Hopefully I'm getting my point across. If you worked on a similar project , I would really appreciate if you can share your examples / tutorials / experience you had making a web-page that takes in value and stores in a database , either SQL, MySQL, access or any DB and guide me please. Any…

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I am working on a membership system. We have added our own in-app-purchase (IAP) plugin to communicate with Apple, Amazon, Google Play and Roku. So far, everything is working as we expect. The issue I am currently having is when I validate the receipt, I want to fetch the membership plan from the product, not a subscription, although I could get it to use that if I must. I have tested with a subscription too but still no luck. Since this will be an automated verification system the subscription seems to be more of a hassle as a simple product seems more ideal for our use case.

I have tried using:

$  _membershipPlan = \wc_memberships_get_memberships_from_subscription($  _productObj); 

Where $ _productObj has been a simple product and a simple subscription but it never returns the membership.

What I am trying to do is once the reciept is validated, I fetch the WC_Product (product or subscription) then I want to see what membership is attached to it and apply this to the user.

I have searched for this in their Docs and on Google and I haven’t been able to find anything. My last resort would be to write my own WP_Query object to handle this, as it seems I might have to do.

Something to note, the method wc_memberships_get_memberships_from_subscription is looking for _subscription_id but the membership doesn’t even have this as meta for it. It does have _product_ids stored in a serialized array which will be annoying to query. Not sure why this would be the case but this is where I am stuck.

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Thank you for your time.

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