how to change priority in ILIKE

Question

I have this simple table and user records.

I just want to get users with ilike or something else to get better order in PostgreSQL 10.12.

CREATE TABLE users(
   ID INT PRIMARY KEY      NOT NULL,
   username           CHAR(50) NOT NULL
);

INSERT INTO users (id, username) VALUES(1,'mandela');
INSERT INTO users (id, username) VALUES(2,'delpiero');
INSERT INTO users (id, username) VALUES(3, 'gondela');
INSERT INTO users (id, username) VALUES(4, 'del');
INSERT INTO users (id, username) VALUES(5, 'dell');
INSERT INTO users (id, username) VALUES(6, 'andel');

When I query "del" I want to get "del" user whose id is 4 in first place. it's ok with ordering by length. But still it is not what I want. The order should be like this. Second order must be "dell", third order must be "delpiero", fourth "andel", fifth "gondela" and sixth "mandela".

select * from users where username ilike '%del%' order by length(users.username) asc;

Here is SQL Fiddle

Answer 1

I would seem to me, that you want leading matches first, then shortest strings first, and finally alphabetic sort order:

SELECT *
FROM   users
WHERE  username ILIKE '%del%'
ORDER  BY username NOT ILIKE 'del%'  -- leading match first
        , length(username)           -- shorter words first
        , username;                  -- finally alphabetical

db<>fiddle here

NOT ILIKE 'del%' because false sorts before true. See:

• Sorting null values after all others, except special

Aside: Never use char(n). See:

• Any downsides of using data type “text” for storing strings?

Answer 2

Maybe something like this:

select * from users where username ilike '%del%' 
   order by strpos(lower(users.username),'del') asc, length(users.username);

But on what basis is tie between "gondela" and "mandela" broken?