SQL - foreach column make slug form different column - sql

Question

I am new with writing complex SQL queries. I am on Postgres 14 and I I am executing migration file which has following concept.
I want to add string field with name slug which will be required like:
$this->addSql('ALTER TABLE tag ADD COLUMN slug VARCHAR NOT NULL');
As the table is already populated and my new column needs to be required
I want to:
Create Null-able column, then update slug table column with valid not null values and finally ALTER column to set NOT NULL constraint!
My table (with potential slug column):
| id | name | type | slug |
|----|------------------|------|------------------|
| 1 | LARPs: The Series| | larps-the-series |
|----|------------------|------|------------------|
| 2 | #MyHaliburton. | | my-haliburton |
Catch:
Added column called “slug” is is a 'slugified' version of the name (all lower case, removed punctuation, spaces replaces with dashes).
I started with:
UPDATE `tag` SET slug = lower(name),
slug = replace(slug, ':', '-'),
slug = replace(slug, '#'', ''),
...
Is this right way to cover all the cases? And yet, how to do it for all fields? Should I use FOR EACH?
Thanks

Answer 1

You can do your slug generation in one command, combining a call to LOWER with two calls to REGEXP_REPLACE, one of which strips leading and trailing non-alphabetic characters, and the other which replaces non-alphabetic characters internal to the string with a - and also inserts a - when a lower-case character is followed by an upper case character:
ALTER TABLE tag ADD COLUMN slug VARCHAR;
UPDATE tag
SET slug = LOWER(
REGEXP_REPLACE(
REGEXP_REPLACE(name, '^[^A-Za-z]+|[^A-Za-z]+$', '', 'g'),
'[^A-Za-z]+|(?<=[a-z])(?=[A-Z])', '-', 'g')
)
;
ALTER TABLE tag ALTER COLUMN slug SET NOT NULL;
Output (for your sample input):
id name type slug
1 LARPs: The Series larps-the-series
2 #MyHaliburton. my-haliburton
Demo on db-fiddle