我需要什么加入？为什么我的查询不起作用？

Question

我想不通为什么我不能在格式的结果，我需要：

我的数据库结构，例如：

CREATE DATABASE IF NOT EXISTS test_b DEFAULT CHARACTER SET utf8mb4 DEFAULT COLLATE utf8mb4_unicode_ci; 
USE test_b; 


CREATE TABLE authors(
    id BIGINT NOT NULL AUTO_INCREMENT, 
    name VARCHAR(100), 
    PRIMARY KEY (id) 
); 
CREATE TABLE galleries(
    id BIGINT NOT NULL AUTO_INCREMENT, 
    title VARCHAR(100), 
    author_id BIGINT NOT NULL, 
    published_at DATETIME, 
    PRIMARY KEY (id) 
); 
CREATE TABLE articles(
    id BIGINT NOT NULL AUTO_INCREMENT, 
    title VARCHAR(100), 
    author_id BIGINT NOT NULL, 
    published_at DATETIME, 
    PRIMARY KEY (id) 
); 

填充一些测试数据到数据库：

INSERT INTO authors (id, name) 
VALUES 
(1, 'Mike'), 
(2, 'John'), 
(3, 'Stan'); 

INSERT INTO galleries (id, title, author_id, published_at) 
VALUES 
(1, 'gallery title 1', 1, now()), 
(2, 'gallery title 2', 1, now()), 
(3, 'gallery title 3', 1, now()), 
(4, 'gallery title 4', 2, now()), 
(5, 'gallery title 5', 2, now()), 
(6, 'gallery title 6', 2, now()), 
(7, 'gallery title 7', 3, now()), 
(8, 'gallery title 8', 3, now()), 
(9, 'gallery title 9', 3, now()); 


INSERT INTO articles (id, title, author_id, published_at) 
VALUES 
(1, 'article title 1', 1, now()), 
(2, 'article title 2', 1, now()), 
(3, 'article title 3', 1, now()), 
(4, 'article title 4', 2, now()), 
(5, 'article title 5', 2, now()), 
(6, 'article title 6', 2, now()), 
(7, 'article title 7', 3, now()), 
(8, 'article title 8', 3, now()), 
(9, 'article title 9', 3, now()), 
(10, 'article title 10', 3, now()), 
(11, 'article title 11', 3, now()), 
(12, 'article title 12', 3, now()); 

我想要显示特定作者的所有已发布内容的表格（作者id = 2），并且我应该可以通过 标题，content_type和已发布的列进行排序：

title,   content_type,  published 
gallery title 4 gallery    DATETIME 
gallery title 5 gallery    DATETIME 
gallery title 6 gallery    DATETIME 
article title 4 article    DATETIME 
article title 5 article    DATETIME 
article title 6 article    DATETIME 

为什么我的查询不起作用？

SELECT 
a.id, 
a.name, 
CONCAT(IF(b.id IS NOT NULL,'gallery',''), IF(c.id IS NOT NULL,'article','')) as content_type, 
CONCAT(COALESCE(b.title, ''), COALESCE(c.title, '')) AS title 
FROM authors as a 
JOIN galleries AS b ON (a.id = b.author_id) 
JOIN articles AS c ON (a.id = c.author_id) 
WHERE a.id = 2; 

Answer 1

我觉得你只是想union all：

select title, 'gallery' as content_type, published_at 
from galleries 
where author_id = 2 
union all 
select title, 'article', published_at 
from articles 
where author_id = 2; 

Answer 2

SELECT Distinct 
a.id, 
a.name, 
CONCAT(IF(b.id IS NOT NULL,'gallery',''), IF(c.id IS NOT NULL,'article','')), 
CONCAT(COALESCE(b.title, ''), COALESCE(c.title, '')) AS title 
FROM authors as a 
JOIN galleries AS b ON a.id = b.author_id 
JOIN articles AS c ON a.id = c.author_id 
where a.id = 2;