Agizo la muungano kwa kutumia syntax/taarifa ya hoja katika hifadhidata ya MySQL

Matumizi ya sintaksia/taarifa ya hifadhidata ya MySQL UNION ORDER BY swala

MySQL Opereta wa UNION

Mafunzo haya yanakuletea sintaksia na mifano ya opereta wa MySQL UNION.

描述

Opereta ya MySQL UNION inatumika kuchanganya matokeo ya kauli mbili au zaidi SELECT katika seti moja ya matokeo.Taarifa nyingi za CHAGUA huondoa nakala za data.

sarufi

Umbizo la sintaksia ya waendeshaji MySQL UNION:

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

参数

• usemi1, usemi2, ... usemi_n: Safu wima ya kurejesha.
• meza: Jedwali la data la kurejesha.
• WAPI masharti: Hiari, vigezo vya utafutaji.
• DISTINCT: Kwa hiari, ondoa nakala ya data kutoka kwa seti ya matokeo.Opereta wa UNION ametoa data kwa chaguomsingi, kwa hivyo kirekebishaji cha DISTINCT hakina athari kwa matokeo.
• ZOTE: Hiari, hurejesha seti zote za matokeo, ikiwa ni pamoja na nakala.

hifadhidata ya demo

Katika somo hili, tutatumia hifadhidata ya sampuli ya chenweiliang.

Hapa kuna data kutoka kwa jedwali la "Tovuti":

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

Hii hapa ni data ya "programu" 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)

Mfano wa SQL UNION

Taarifa ifuatayo ya SQL huchagua nchi zote tofauti (thamani tofauti pekee) kutoka kwa jedwali la "Tovuti" na "programu" :

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

SQL UNION mfano WOTE

Taarifa ifuatayo ya SQL inatumia UNION ALL kuchagua nchi zote (ikiwa ni pamoja na thamani zinazorudiwa) kutoka kwa jedwali la "Tovuti" na "programu" :

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

SQL UNION ALL na WHERE

Taarifa ifuatayo ya SQL inatumia UNION ALL kuchagua data yote ya China (CN) kutoka kwa jedwali la "Tovuti" na "programu" (ikiwa ni pamoja na thamani zinazorudiwa):

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