Ukuhleleka kwenyunyana ngokusetshenziswa kwe-syntax/isitatimende kusizindalwazi se-MySQL

Ukusetshenziswa kwe-syntax/isitatimende sedatha ye-MySQL i -UNION ORDER BY query

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 se-SQL esilandelayo sikhetha wonke amazwe ahlukene (amanani ahlukile kuphela) kumathebula "Amawebhusayithi" kanye "nezinhlelo zokusebenza" :

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

I-SQL UNION SONKE isibonelo

Isitatimende se-SQL esilandelayo sisebenzisa i-UNION ALL ukukhetha wonke amazwe (kufaka phakathi amanani aphindaphindwayo) kusukela kuthebula elithi "Amawebhusayithi" kanye "nezinhlelo zokusebenza" :

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

I-SQL UNION KONKE nge-WHERE

Isitatimende se-SQL esilandelayo sisebenzisa i-UNION ALL ukukhetha yonke idatha ye-China (CN) kusukela ku-"Amawebhusayithi" kanye "nama-apps" amathebula (kufaka phakathi amanani aphindaphindwayo):

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