Odar ƙungiyar ta hanyar tambaya syntax/amfani da magana a cikin bayanan MySQL

MySQL databaseOdar ƙungiyar ta hanyar tambaya syntax/amfani da magana

MySQL Ma'aikacin UNION

Wannan koyawa tana gabatar muku da ma'auni da misalan ma'aikacin MySQL UNION.

bayanin

Ana amfani da ma'aikacin MySQL UNION don haɗa sakamakon biyu ko fiye da bayanan SELECT cikin saitin sakamako guda ɗaya.Maganganun SELECT da yawa suna cire kwafin bayanai.

nahawu

Tsarin tsarin ma'aikaci na MySQL UNION:

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

Matsayi

• magana1, magana2, ... magana_n: Rukunin da za a ɗauko.
• tebur: Teburin bayanan don dawo da shi.
• INA sharadi: Na zaɓi, ma'aunin bincike.
• RABA: Zabi, cire kwafin bayanai daga saitin sakamako.Ma'aikacin UNION ya cire bayanan ta tsohuwa, don haka mai gyara DISTINCT ba shi da wani tasiri akan sakamakon.
• DUK: Na zaɓi, yana dawo da duk saitin sakamako, gami da kwafi.

demo database

A cikin wannan koyawa, za mu yi amfani da ma'aunin bayanai na chenweiliang.

Ga bayanai daga teburin "Shafukan Yanar Gizo":

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

Ga bayanan don "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)

Misalin SQL UNION

Bayanin SQL mai zuwa yana zaɓar duk daga cikin "Shafukan Yanar Gizo" da "apps" teburdaban-dabanƙasa (ƙimomi daban-daban kawai):

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

SQL UNION DUK misali

Bayanin SQL mai zuwa yana amfani da UNION ALL don zaɓar daga "Shafukan Yanar Gizo" da "apps" teburdukaƙasa (kuma tana da ƙima iri-iri):

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

SQL UNION DUK tare da INA

Bayanin SQL mai zuwa yana amfani da UNION ALL don zaɓar daga "Shafukan Yanar Gizo" da "apps" teburdukaBayanai na China (CN) (kuma tare da ƙima mai ƙima):

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