How do I convert a T-SQL query to PostgreSQL that concatenates substrings? - sql

Question

This is my query:
SELECT
*,
CONCAT(
RIGHT( account_no, 4),
RIGHT( customer_id, 5 )
) AS "password for my diplomo"
FROM
account_info;
But I get this error:
Error: function left(bigint, integer) does not exist;
My table is:
CREATE TABLE account_info (
account_no bigint NOT NULL PRIMARY KEY,
customer_id varchar(...)
)

Answer 1

Postgres functions left and right expect their first argument be text.
So first cast account_no to type text and your query (a bit simplified) will work.
SELECT *,
right(account_no::text, 4) || right(customer_id, 5) as pfmd
FROM account_info;
Unrelated but the best practice under Postgres is to use type text instead of char or varchar.

Answer 2

You seem to be using a reference for T-SQL or JET Red SQL (for MS SQL Server and MS Access respectively) when you're actually using PostgreSQL which uses completely different functions (and syntax) for string/text processing.
This is the PostgreSQL v12 manual page for string functions and other syntax. You should read it.
As for making your query run on PostgreSQL, change it to this:
Convert account_no to a varchar type so you can use SUBSTRING with it.
I think it might work without it, but I don't like relying on implicit conversion, especially when localization/locale/culture issues might pop-up.
The LEFT and RIGHT functions for extracting substrings can be reimplemented like so:
LEFT( text, length ) == SUBSTRING( text FROM 0 FOR length )
RIGHT( text, length ) == SUBSTRING( text FROM CHAR_LENGTH( text ) - length )
And use || to concatenate text values together.
Like so:
SELECT
q.*,
(
SUBSTRING( q.account_no_text FROM CHAR_LENGTH( q.account_no_text ) - 4 )
||
SUBSTRING( q.customer_id FROM CHAR_LENGTH( q.customer_id ) - 5 )
) AS "password for my diplomo"
FROM
(
SELECT
ai.*,
ai.account_no::varchar(10) AS account_no_text
FROM
account_info AS ai
)
AS q
Here is a runnable DB-Fiddle.
Screenshot proof: