Taelo ea bonngoe ka tšebeliso ea mantsoe a mantsoe / polelo ho database ea MySQL

MySQL databaseTaelo ea kopano ka tšebeliso ea polelo ea polelo / polelo

MySQL UNION opareitara

Thupelo ena e u tsebisa ka syntax le mehlala ea opareitara ea MySQL UNION.

tlhaloso

MySQL UNION opareitara e sebelisoa ho kopanya liphetho tsa lipolelo tse peli kapa ho feta tsa KHETHA hore e be sephetho se le seng.Lipolelo tse ngata tsa KHETHA li tlosa lintlha tse kopitsoang.

sebōpeho-puo

Sebopeho sa syntax sa MySQL UNION:

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

Paramente

• polelo1, polelo2, ... polelo_n: Kholomo e tla khutlisoa.
• litafole: Tafole ea data e tla khutlisoa.
• MANE maemo: Boikhethelo, mekhoa ea ho batla.
• DISTINCT: Ka boikhethelo, tlosa data e kopitsoang ho tsoa sehlopheng sa sephetho.Opereishene ea UNION e kopile lintlha ka mokhoa o ikhethileng, kahoo DISTINCT modifier ha e na phello ho sephetho.
• TSOHLE: Ha u khetha, e khutlisa liphetho tsohle, ho kenyeletsoa le tse kopitsoang.

database ea demo

Thutong ena, re tla sebelisa database ea sampole ea chenweiliang.

Lintlha tse tsoang tafoleng ea "Liwebsaete" ke tsena:

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     |
+----+---------------+---------------------------+-------+---------+

Lintlha tsa "apps" APP ke tsena:

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)

Mohlala oa SQL UNION

Polelo e latelang ea SQL e khetha tsohle ho tsoa litafoleng tsa "Website" le "apps".fapanenaha (litekanyetso tse ikhethileng feela):

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

Mohlala oa SQL UNION TSOHLE

Polelo e latelang ea SQL e sebelisa UNION ALL ho khetha ho tsoa ho "Websites" le "apps" litafolekaofelanaha (e boetse e na le boleng bo habeli):

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

SQL UNION TSOHLE le MOKAE

Polelo e latelang ea SQL e sebelisa UNION ALL ho khetha ho tsoa ho "Websites" le "apps" litafolekaofelaLintlha tsa China (CN) (hape li na le boleng bo habeli):

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