Constructing a string out of several records with 2 columns

问题

I have prepared a simple SQL Fiddle for my question -

In a word game written in Pl/pgSQL for PostgreSQL 10.2 player moves are stored in the table:

CREATE TABLE words_scores (
        mid     bigint  NOT NULL REFERENCES words_moves ON DELETE CASCADE,
        gid     integer NOT NULL REFERENCES words_games ON DELETE CASCADE,
        uid     integer NOT NULL REFERENCES words_users ON DELETE CASCADE,
        word    text    NOT NULL CHECK(word ~ '^[A-Z]{2,}$'),
        score   integer NOT NULL CHECK(score >= 0)
);

Here it is filled with some test data:

INSERT INTO words_scores (mid, gid, uid, word, score) VALUES
   (230, 209, 7, 'XY',  5),
   (230, 209, 7, 'XYZ', 15),
   (230, 209, 7, 'XAB', 13);

In a stored function I need to generate a string, which would contain all words played by a player in a certain move.

This is close to what I need and returns XY, XYZ, XAB:

SELECT STRING_AGG(word, ', ') FROM words_scores WHERE mid=230;

However I also need to have the score of each word in brackets, following each words as in:

XY (5), XYZ (15), XAB (13)

Is there maybe some clever use of Aggregate Functions possible to achieve that?

回答1:

Use FORMAT (as described in the manual) to format your string before aggregation:

SELECT STRING_AGG(FORMAT('%s (%s)', word, score), ', ') FROM words_scores WHERE mid=230;

Here's the updated SQL Fiddle.

来源：https://stackoverflow.com/questions/49009775/constructing-a-string-out-of-several-records-with-2-columns