Saraka ya Nakala
Hifadhidata ya MySQLAgizo la Muungano kwa kutumia syntax ya hoja/taarifa
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 zote kutoka kwa majedwali ya "Tovuti" na "programu".tofautinchi (thamani tofauti pekee):
Mfano
SELECT country FROM Websites UNION SELECT country FROM apps ORDER BY country;
SQL UNION mfano WOTE
Taarifa ifuatayo ya SQL hutumia UNION ALL kuchagua kutoka kwa majedwali ya "Tovuti" na "programu".yotenchi (pia ina maadili yanayorudiwa):
Mfano
SELECT country FROM Websites UNION ALL SELECT country FROM apps ORDER BY country;
SQL UNION ALL na WHERE
Taarifa ifuatayo ya SQL hutumia UNION ALL kuchagua kutoka kwa majedwali ya "Tovuti" na "programu".yoteData ya Uchina (CN) (pia yenye thamani rudufu):
Mfano
SELECT country, name FROM Websites WHERE country='CN' UNION ALL SELECT country, app_name FROM apps WHERE country='CN' ORDER BY country;
Hope Chen Weiliang Blog ( https://www.chenweiliang.com/ ) ilishirikiwa "agizo la muungano kwa kutumia syntax/taarifa ya hoja katika hifadhidata ya MySQL", ambayo ni muhimu kwako.
Karibu kushiriki kiungo cha makala hii:https://www.chenweiliang.com/cwl-475.html
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