Aṣẹ ẹgbẹ nipasẹ ibeere sintasi/lilo alaye ni aaye data MySQL

MySQL databaseIlana iṣọkan nipasẹ ibeere sintasi / lilo alaye

MySQL Oṣiṣẹ UNION

Ikẹkọ yii ṣafihan ọ si sintasi ati awọn apẹẹrẹ ti oniṣẹ MySQL UNION.

apejuwe

Oṣiṣẹ MySQL UNION ni a lo lati ṣajọpọ awọn abajade ti awọn alaye YAN meji tabi diẹ sii sinu eto abajade ẹyọkan.Awọn alaye YAN pupọ yọ awọn data ẹda-iwe kuro.

girama

MySQL UNION ọna kika sintasi oniṣẹ:

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

Apaadi

• ikosile1, ikosile2, ... ikosile_n: Ọwọn lati gba pada.
• awọn tabili: Tabili data lati gba pada.
• Nibo awọn ipo: Iyan, àwárí àwárí mu.
• YÀTỌ: Ni iyan, yọ data ẹda-iwe kuro ninu eto abajade.Oniṣẹ UNION ti yọkuro data nipasẹ aiyipada, nitorinaa iyipada DISTINCT ko ni ipa lori abajade.
• GBOGBO: Iyan, da gbogbo awọn eto abajade pada, pẹlu awọn ẹda-ẹda.

demo database

Ninu ikẹkọ yii, a yoo lo aaye data ayẹwo chenweiliang.

Eyi ni data lati tabili "Awọn aaye ayelujara":

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

Eyi ni data fun “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)

SQL UNION apẹẹrẹ

Gbólóhùn SQL atẹle yii yan gbogbo rẹ lati awọn tabili “Awọn oju opo wẹẹbu” ati “awọn ohun elo”.yatọorilẹ-ede (awọn iye pato nikan):

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

SQL UNION GBOGBO apẹẹrẹ

Gbólóhùn SQL atẹle yii nlo UNION ALL lati yan lati awọn tabili “Awọn oju opo wẹẹbu” ati “awọn ohun elo”.gbogboorilẹ-ede (tun ni awọn iye ẹda-ẹda):

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

SQL UNION GBOGBO pẹlu Nibo

Gbólóhùn SQL atẹle yii nlo UNION ALL lati yan lati awọn tabili “Awọn oju opo wẹẹbu” ati “awọn ohun elo”.gbogboData fun China (CN) (tun pẹlu awọn iye ẹda-ẹda):

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