Ordo unionis per interrogationem syntaxin/enuntiationis usus in MySQL database

Usus syntaxis interrogationis/enuntiati UNION ORDER BY in basi datorum MySQL

MySQL CONIUNCTIO operator

Haec doceo te ad syntaxin et exempla MySQL Unionis operantis introducit.

Description

Operator MySQL CONIUNCTIO adhibetur ad coniungendos eventus duorum vel plurium propositionum selectarum in unum effectum statutorum.Multae sententiae selectae duplicata data removent.

grammatica

MySQL CONIUNCTIO operator format syntaxin:

SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions]
UNION [ALL | DISTINCT]
SELECT expression1, expression2, ... expression_n
FROM tables
[WHERE conditions];

Morbi

• expression1, expression2, ... expression_n: columnam capias.
• Tabulae: Data mensa capias.
• Ubi conditiones: Libitum, criteria quaestionis denota.
• DISTINCTUS: Optionally, data duplicata remove ab eventu statuto.CONGREGATIO operator data per defaltam duplicavit, ergo determinatio distincti effectus nullum effectum habet.
• OMNIS: Ad libitum, omnes proventus effectus recurrit, duplicata possidet.

demo database

In hoc doceo, chenweiliang specimen datorum utemur.

Hic est notitia e mensa "Websitarum":

mysql> SELECT * FROM Websites;
+----+--------------+---------------------------+-------+---------+
| id | name         | url                       | alexa | country |
+----+--------------+---------------------------+-------+---------+
| 1  | Google       | https://www.google.cm/    | 1     | USA     |
| 2  | 淘宝          | https://www.taobao.com/   | 13    | CN      |
| 3  | 陈沩亮博客      | http://www.chenweiliang.com/    | 4689  | CN      |
| 4  | 微博          | http://weibo.com/         | 20    | CN      |
| 5  | Facebook     | https://www.facebook.com/ | 3     | USA     |
| 7  | stackoverflow | http://stackoverflow.com/ |   0 | IND     |
+----+---------------+---------------------------+-------+---------+

Hic est notitia pro "apps" APP:

mysql> SELECT * FROM apps;
+----+------------+-------------------------+---------+
| id | app_name   | url                     | country |
+----+------------+-------------------------+---------+
|  1 | QQ APP     | http://im.qq.com/       | CN      |
|  2 | 微博 APP | http://weibo.com/       | CN      |
|  3 | 淘宝 APP | https://www.taobao.com/ | CN      |
+----+------------+-------------------------+---------+
3 rows in set (0.00 sec)

SQL CONIUNCTIO exempli gratia

Sequens mandatum SQL omnes distinctas terras (solum valores distinctos) ex tabulis "Websites" et "apps" deligit:

SELECT country FROM Websites
UNION
SELECT country FROM apps
ORDER BY country;

SQL CONIUNCTIO OMNES exempli gratia

Sequens enuntiatio SQL UNION ALL adhibet ad omnes terras (valores duplicatos inclusis) ex tabulis "Websites" et "apps" eligendas:

SELECT country FROM Websites
UNION ALL
SELECT country FROM apps
ORDER BY country;

SQL CONIUNCTIO OMNES cum WHERE

Sequens mandatum SQL UNION ALL adhibet ad omnia data pro Sinis (CN) ex tabulis "Websites" et "apps" (valoribus duplicatis inclusis) eligenda:

SELECT country, name FROM Websites
WHERE country='CN'
UNION ALL
SELECT country, app_name FROM apps
WHERE country='CN'
ORDER BY country;