Inyon lòd pa itilizasyon sentaks/deklarasyon rechèch nan baz done MySQL

baz done MySQLLòd Inyon pa itilizasyon sentaks/deklarasyon rechèch

Miskl UNION operatè

Tutorial sa a prezante w sentaks ak egzanp operatè UNION MySQL.

描述

Yo itilize operatè MySQL UNION pou konbine rezilta de oswa plis SELECT deklarasyon nan yon seri rezilta sèl.Deklarasyon SELECT miltip retire done kopi.

gramè

Fòma sentaks operatè 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

• ekspresyon1, ekspresyon2, ... ekspresyon_n: Kolòn pou rekipere.
• tab: Tablo done pou rekipere.
• KOTE kondisyon: Si ou vle, kritè rechèch.
• DISTINTE: Opsyonèlman, retire done kopi nan seri rezilta a.Operatè UNION an gen done deduplike pa default, kidonk modifikatè DISTINCT la pa gen okenn efè sou rezilta a.
• TOUT: Si ou vle, retounen tout seri rezilta yo, ki gen ladan kopi.

baz done Demo

Nan leson patikilye sa a, nou pral sèvi ak baz done echantiyon chenweiliang la.

Men done ki soti nan tablo "Sit Web" yo:

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

Men done pou APP "apps" la:

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 egzanp

Deklarasyon SQL sa a chwazi tout nan tab "Sit wèb" ak "aplikasyon".diferanpeyi (valè diferan sèlman):

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

SQL UNION TOUT egzanp

Deklarasyon SQL sa a itilize UNION ALL pou chwazi nan tab "Sit Web" ak "aplikasyon".toutpeyi (tou gen valè kopi):

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

SQL UNION TOUT ak KOTE

Deklarasyon SQL sa a itilize UNION ALL pou chwazi nan tab "Sit Web" ak "aplikasyon".toutDone pou Lachin (CN) (tou ak valè kopi):

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