SQLite UNION ALL 运算符

SQLite 中的 UNION ALL 运算符用于结合两个 SELECT 语句的结果,包括重复行

UNION ALL 类似于 UNION,不同的是它可以有重复的行

语法

UNION ALL 的语法规则如下

SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]

UNION ALL

SELECT column1 [, column2 ]
FROM table1 [, table2 ]
[WHERE condition]

为了使用 UNION ALL ,每个 SELECT 被选择的列数必须是相同的,相同数目的列表达式,相同的数据类型,并确保它们有相同的顺序,但它们不必具有相同的长度

范例

先运行下面的 SQL 语句创建测试数据

DROP TABLE IF EXISTS `tbl_language`;
DROP TABLE IF EXISTS `tbl_rank`;

CREATE TABLE IF NOT EXISTS `tbl_language`(
   `id` INT UNSIGNED AUTO_INCREMENT,
   `name` VARCHAR(64) NOT NULL,
   `url` VARCHAR(128) NOT NULL,
   `founded_at` DATE,
   PRIMARY KEY ( `id` )
);

CREATE TABLE IF NOT EXISTS `tbl_rank`(
   `id` INT UNSIGNED AUTO_INCREMENT,
   `name` VARCHAR(64) NOT NULL,
   `month` VARCHAR(7) NOT NULL,
   `rank` TINYINT NOT NULL,
   `rate` VARCHAR(32) NOT NULL,
   PRIMARY KEY ( `id` )
);

INSERT INTO `tbl_language` VALUES
    (1,'Python','https://www.twle.cn','1991-2-20'),
    (2,'PHP','http://www.php.net','1994-1-1'),
    (3,'Ruby','https://www.ruby-lang.org/','1996-12-25');

INSERT INTO `tbl_rank` VALUES
    (1, 'Python','2018-04',4,'5.083%'),
    (2, 'PHP','2018-04',6,'4.218%'),
    (3, 'Ruby','2018-04',11,'2.018%'),
    (4, 'Java','2018-04',1,'15.777%'),
    (5, 'Python','2018-03',4,'5.869%'),
    (6, 'PHP','2018-03',7,'4.010%'),
    (7, 'Ruby','2018-03',12,'2.744%'),
    (8, 'Java','2018-03',1,'14.941'),
    (9, 'Python','2018-02',4,'5.168%'),
    (10, 'PHP','2018-02',7,'3.420%'),
    (11, 'Ruby','2018-02',10,'2.534%'),
    (12, 'Java','2018-02',1,'14.988%');

tbl_language 表中的数据如下

+----+--------+----------------------------+------------+
| id | name   | url                        | founded_at |
+----+--------+----------------------------+------------+
|  1 | Python | https://www.twle.cn        | 1991-02-20 |
|  2 | PHP    | http://www.php.net         | 1994-01-01 |
|  3 | Ruby   | https://www.ruby-lang.org/ | 1996-12-25 |
+----+--------+----------------------------+------------+

tbl_rank 表中的数据如下

+----+--------+---------+------+---------+
| id | name   | month   | rank | rate    |
+----+--------+---------+------+---------+
|  1 | Python | 2018-04 |    4 | 5.083%  |
|  2 | PHP    | 2018-04 |    6 | 4.218%  |
|  3 | Ruby   | 2018-04 |   11 | 2.018%  |
|  4 | Java   | 2018-04 |    1 | 15.777% |
|  5 | Python | 2018-03 |    4 | 5.869%  |
|  6 | PHP    | 2018-03 |    7 | 4.010%  |
|  7 | Ruby   | 2018-03 |   12 | 2.744%  |
|  8 | Java   | 2018-03 |    1 | 14.941  |
|  9 | Python | 2018-02 |    4 | 5.168%  |
| 10 | PHP    | 2018-02 |    7 | 3.420%  |
| 11 | Ruby   | 2018-02 |   10 | 2.534%  |
| 12 | Java   | 2018-02 |    1 | 14.988% |
+----+--------+---------+------+---------+

下面的 SQL 语句从 tbl_languagetbl_rank 表中选取所有的 name(可能有重复的值)

SELECT name FROM tbl_language UNION ALL SELECT name FROM tbl_rank  ORDER BY name;

执行以上 SQL 输出结果如下

name      
----------
Java      
Java      
Java      
PHP       
PHP       
PHP       
PHP       
Python    
Python    
Python    
Python    
Ruby      
Ruby      
Ruby      
Ruby

SQLite 基础教程

关于   |   FAQ   |   我们的愿景   |   广告投放   |  博客

  简单教程,简单编程 - IT 入门首选站

Copyright © 2013-2022 简单教程 twle.cn All Rights Reserved.