PostgreSQL pattern matching with Unicode graphemes - postgresql

Question

Is there any way to pattern match with Unicode graphemes?
As a quick example, when I run this query:
CREATE TABLE test (
id SERIAL NOT NULL,
name VARCHAR NOT NULL,
PRIMARY KEY (id),
UNIQUE (name)
);
INSERT INTO test (name) VALUES ('👍🏻 One');
INSERT INTO test (name) VALUES ('👍 Two');
SELECT * FROM public.test WHERE test.name LIKE '👍%';
I get both rows returned, rather than just '👍 Two'. Postgres seems to be just comparing code points, but I want it to compare full graphemes, so it should only match '👍 Two', because 👍🏻 is a different grapheme.
Is this possible?

Answer 1

It's a very interesting question!
I am not quite sure if it is possible anyway:
The skinned emojis are, in fact, two joined characters (like ligatures). The first character is the yellow hand 👍 which is followed by an emoji skin modifier 🏻
This is how the light skinned hand is stored internally. So, for me, your result makes sense:
When you query any string, that begins with 👍, it will return:
👍 Two (trivial)
👍_🏻 One (ignore the underscore, I try to suppress the automated ligature with this)
So, you can see, the light skinned emoji internally also starts with 👍. That's why I believe, that your query doesn't work the way you like.
Workarounds/Solutions:
You can add a space to your query. This ensures, that there's no skin modifier after your 👍 character. Naturally, this only works in your case, where all data sets have a space after the hand:
SELECT * FROM test WHERE name LIKE '👍 %';
You can simply extend the WHERE clause like this:
SELECT * FROM test
WHERE name LIKE '👍%'
AND name NOT LIKE '👍🏻%'
AND name NOT LIKE '👍🏼%'
AND name NOT LIKE '👍🏽%'
AND name NOT LIKE '👍🏾%'
AND name NOT LIKE '👍🏿%'
You can use regular expression pattern matching to exclude the skins:
SELECT * FROM test
WHERE name ~ '^👍[^🏻🏼🏽🏾🏿]*$'
see demo:db<>fiddle (note that the fiddle seems not to provide automated ligatures, so both characters are separated displayed there)