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PHP Integrating PHP with Databases Limiting Records in SQL Filtering Data by Category

Posted by Matt Nickolls
Matt Nickolls
9,895 Points

Nested vs unnested Replace Query

Hi all

In relation to the nested replace removing the prepositions Would it make any difference to the output if rather than using:

"SELECT media_id, title, category, img FROM Media WHERE category = ?"); ORDER BY REPLACE( REPLACE( REPLACE(title, 'The ',' ') 'An ', ' '),'A ', ' '))";

We used unnested replaces like this:

REPLACE (title, 'The ', ' '); REPLACE( title, 'An ', ' ' ); REPLACE( title, 'A ', ' ' );

Just can't wrap my head around why we need to nest them.

Thanks for your time.

1 Answer

Peter Vann
Peter Vann
36,425 Points
Peter Vann
Peter Vann
36,425 Points

Hi Matt!

I hope I can make this make sense.

You are ordering by title, which you only reference once, in the innermost REPLACE, which filters out "The" in the ORDER BY sorting.

Then, the same title (void of "The") is passed to the next/parent REPLACE to filter out "An".

Then, the same title (void of both "The" and/or "An") is passed to the next/parent REPLACE to filter out "A".

In the end, you end up sorting by each catalog item's title, ignoring any "The", "An", and/or "A" that could be in it.

Another way to think of it is that the result of the innermost REPLACE becomes the first argument in the parent REPLACE, etc. all the way up the REPLACE nesting chain.

To visualize in JavaScript, it would be similar to this:

  var title = "The An A Catalog Title"; 
  title = title.replace("The ", "");
  title = title.replace("An ", "");
  title = title.replace("A ", "");
  console.log(title);

Which will log:

Catalog Title

title being what each title would look like to the ORDER BY sort

Does that make sense?

More info:

https://bertwagner.com/posts/how-to-eliminate-ugly-nested-replace-functions/

I hope that helps.

Stay safe and happy coding!