Question

在我的应用中，用户

CREATE TABLE users (
    id bigserial PRIMARY KEY,
    username varchar(50) NOT NULL
);

可以发送消息

CREATE TABLE messages (
    id bigserial PRIMARY KEY,
    from_id bigint NOT NULL REFERENCES users ON DELETE RESTRICT,
    body text NOT NULL CHECK (body <> ''),
    created_at timestamp(0) NOT NULL DEFAULT LOCALTIMESTAMP(0),
    is_read boolean NOT NULL DEFAULT TRUE
);

对许多收件人

CREATE TABLE message_recipients (
    message_id bigint NOT NULL REFERENCES messages ON DELETE CASCADE,
    user_id bigint NOT NULL REFERENCES users ON DELETE RESTRICT,
    is_read boolean NOT NULL DEFAULT FALSE,
    PRIMARY KEY (message_id, user_id)
);

如何选择多个用户之间发送的邮件，以便is_read列指定其中一个用户是否已阅读邮件？我还想包含一个名为to_ids的列，其中包含以逗号分隔的邮件收件人用户ID列表。

，例如，如何获取用户1,2和3之间发送的消息，以便is_read列指定用户1是否已阅读消息？ to_ids列包含来自集{1, 2, 3}的两个以逗号分隔的ID。

结果集应包含以下列：id, from_id, to_ids, body, created_at, is_read。

样本数据

SELECT * FROM users;
#  id |  username  | 
# ----+------------+
#   1 | user1      |
#   2 | user2      |
#   3 | user3      |

SELECT * FROM messages;
#  id | from_id |       body          |     created_at      | is_read
# ----+---------+---------------------+---------------------+---------
#   1 |       1 | This is message 1.  | 2016-12-16 11:41:50 | t
#   2 |       2 | This is message 2.  | 2016-12-16 11:41:50 | t
#   3 |       3 | This is message 3.  | 2016-12-16 11:41:50 | t
#   4 |       1 | This is message 4.  | 2016-12-16 11:41:50 | t
#   5 |       2 | This is message 5.  | 2016-12-16 11:41:50 | t
#   6 |       3 | This is message 6.  | 2016-12-16 11:41:50 | t
#   7 |       1 | This is message 7.  | 2016-12-16 11:41:50 | t

SELECT * FROM message_recipients;
#  message_id | user_id | is_read 
# ------------+---------+---------
#           1 |       2 | f
#           1 |       3 | f
#           2 |       1 | f
#           2 |       3 | f
#           3 |       1 | f
#           3 |       2 | f
#           4 |       2 | f
#           4 |       3 | f
#           5 |       1 | f
#           5 |       3 | f
#           6 |       1 | f
#           6 |       2 | f
#           7 |       2 | f
#           7 |       3 | f

预期产出

#  id | from_id | to_ids |       body          |     created_at      | is_read
# ----+---------+--------+---------------------+---------------------+---------
#   1 |       1 |    2,3 | This is message 1.  | 2016-12-16 11:41:50 | t
#   2 |       2 |    1,3 | This is message 2.  | 2016-12-16 11:41:50 | f
#   3 |       3 |    1,2 | This is message 3.  | 2016-12-16 11:41:50 | f
#   4 |       1 |    2,3 | This is message 4.  | 2016-12-16 11:41:50 | t
#   5 |       2 |    1,3 | This is message 5.  | 2016-12-16 11:41:50 | f
#   6 |       3 |    1,2 | This is message 6.  | 2016-12-16 11:41:50 | f
#   7 |       1 |    2,3 | This is message 7.  | 2016-12-16 11:41:50 | t

当我是众多邮件收件人之一时获取is_read

0 个答案: