Update telephone number format to include country identifier - postgresql

Question

Being a beginner in SQL, I am trying to do the telephone fields to be noted in the format: '"+" + country identifier + telephone number'.
UPDATE public.contact
SET phone_number = CASE WHEN (country_code ='FR')
AND phone_number NOT LIKE '+33%'
AND phone_number <> NULL
THEN CONCAT('+33', phone_number)
WHEN (country_code ='GB')and phone_number NOT LIKE '+44%'
AND phone_number <> NULL
THEN CONCAT('+44', phone_number)
I want to update telephone number format to include country identifier like : 0606080905-> [phone] if country_code='FR' . I am looking for a faster and less complex way than what I did.

Answer 1

You can do this with a regular expression using regexp_replace.
Imagine your data being:
+----------+--------------+
Table 'numbers': | country | phone |
+----------+--------------+
| FR | 0606080905 |
| FR | [phone] |
| GB | 0123456789 |
| GB | [phone] |
| GB | NULL |
+----------+--------------+
Then the following update would replace the leading 0 with the country code +33 for all numbers that do not start with a +xx and have FR as country.
UPDATE numbers
SET phone = REGEXP_REPLACE(trim(phone), '^(0)', '+33')
WHERE country = 'FR'
Explained:
the ^ means start of the string
the (0) is the match that gets replaced (leading zero)
the +33 is the string that is used to replace it
the trim() is just added for safety, in case there are leading spaces
NULL phone numbers won't be affected, as they do not match
You could do this now as you did before with a CASE WHEN or something similar for each of the different possibilities. But since the expression always is the same, an easier way would be to have your country codes and their numerical mapping in a separate table:
+----------+--------+
Table 'mapping': | country | prefix |
+----------+--------+
| FR | +33 |
| GB | +44 |
+----------+--------+
You could then do
UPDATE numbers n
SET phone = REGEXP_REPLACE(trim(phone), '^(0)', prefix)
FROM mapping m
WHERE m.country = n.country
and update all your numbers in one go:
+----------+--------------+
| country | phone |
+----------+--------------+
| FR | [phone] |
| FR | [phone] |
| GB | [phone] |
| GB | [phone] |
| GB | NULL |
+----------+--------------+
EDIT: Previously, I had this needlessly complicated answer. You may need something like this if your phone number patterns are more diverse...
The following update would replace the leading 0 with the country code +33 for all numbers that do not start with a +xx and have FR as country.
UPDATE numbers
SET phone = REGEXP_REPLACE(trim(phone), '^(?<![+\d{2}])(0)', '+33')
WHERE country = 'FR'
Explained:
the (?<![+]) is a negative lookbehind assertion that makes sure the regex only matches if there is no + followed by two digits before
the (0) is the match that gets replaced
the +33 is the string that is used to replace it
the trim() is just added for safety, in case there are leading spaces
NULL phone numbers won't be affected, as they do not match

Answer 2

That's about as simple as it gets.
The only way I can imagine to speed up processing is to add a WHERE condition that avoids updating the rows that don't have to be modified.
You could also run several such statements in parallel, where each modifies a different part of the table.
As mentioned in the comment, <> NULL is never true.