Uhla lwemibhalo ye-athikili
MySQL databaseI-Union order ngombuzo we-syntax/isitatimende sokusetshenziswa
MySQL UNION opharetha
Lesi sifundo sikwethulela ku-syntax nezibonelo ze-opharetha ye-MySQL UNION.
incazelo
Umsebenzisi we-MySQL UNION usetshenziselwa ukuhlanganisa imiphumela yezitatimende ezimbili noma ngaphezulu KHETHA zibe yisethi yomphumela owodwa.Izitatimende eziningi KHETHA zisusa idatha eyimpinda.
uhlelo lolimi
Ifomethi ye-syntax yomsebenzisi we-MySQL UNION:
SELECT expression1, expression2, ... expression_n FROM tables [WHERE conditions] UNION [ALL | DISTINCT] SELECT expression1, expression2, ... expression_n FROM tables [WHERE conditions];
Ipharamitha
- expression1, expression2, ... expression_n: Ikholomu ezolandwa.
- amatafula: Ithebula ledatha elizotholwa.
- LAPHO izimo: Ongakukhetha, imibandela yokusesha.
- DISTINCT: Ongakukhetha, susa idatha eyimpinda kusethi yemiphumela.Umsebenzisi we-UNION ukhiphe idatha ngokuzenzakalelayo, ngakho-ke isilungisi se-DISTINCT asinawo umthelela kumphumela.
- BONKE: Ongakukhetha, ibuyisela wonke amasethi wemiphumela, okuhlanganisa nezimpinda.
demo database
Kulesi sifundo, sizosebenzisa isampula yedatha ye-chenweiliang.
Nansi idatha evela kuthebula elithi "Amawebhusayithi":
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 | +----+---------------+---------------------------+-------+---------+
Nansi idatha ye-APP "yezinhlelo zokusebenza":
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)
Isibonelo se-SQL UNION
Isitatimende esilandelayo se-SQL sikhetha konke kumathebula "Amawebhusayithi" kanye "nezinhlelo zokusebenza".kwehlukileizwe (amanani ahlukile kuphela):
Isibonelo
SELECT country FROM Websites UNION SELECT country FROM apps ORDER BY country;
I-SQL UNION SONKE isibonelo
Isitatimende esilandelayo se-SQL sisebenzisa i-UNION ALL ukuze ukhethe kumathebula "Amawebhusayithi" kanye "nezinhlelo zokusebenza".konkeizwe (liphinde libe namanani ayimpinda):
Isibonelo
SELECT country FROM Websites UNION ALL SELECT country FROM apps ORDER BY country;
I-SQL UNION KONKE nge-WHERE
Isitatimende esilandelayo se-SQL sisebenzisa i-UNION ALL ukuze ukhethe kumathebula "Amawebhusayithi" kanye "nezinhlelo zokusebenza".konkeIdatha yase-China (CN) (futhi enamanani ayimpinda):
Isibonelo
SELECT country, name FROM Websites WHERE country='CN' UNION ALL SELECT country, app_name FROM apps WHERE country='CN' ORDER BY country;
I-Hope Chen Weiliang Blog ( https://www.chenweiliang.com/ ) kwabiwe "ukuhleleka kwenyunyana ngokusetshenziswa kwe-syntax/isitatimende kusizindalwazi se-MySQL", okuwusizo kuwe.
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