Nested vs unnested Replace Query

Question

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.

Peter Vann · Answer

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:
javascript
  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!

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Matt Nickolls

Matt Nickolls

Nested vs unnested Replace Query

1 Answer

Peter Vann

Peter Vann