ʻO ka hui ʻana ma ka hoʻohana ʻana i ka syntax / ʻōlelo hoʻohana i ka waihona MySQL

MySQL waihonaHoʻonohonoho hui ʻia ma ka hoʻohana ʻana i ka syntax / ʻōlelo

MySQL mea hoʻohana UNION

Hōʻike kēia kumu aʻo iā ʻoe i ka syntax a me nā hiʻohiʻona o ka mea hoʻohana MySQL UNION.

ho'ākāka

Hoʻohana ʻia ka mea hoʻohana MySQL UNION e hoʻohui i nā hopena o ʻelua mau huaʻōlelo SELECT i loko o kahi hoʻonohonoho hopena.Hoʻopau nā ʻōlelo SELECT he nui i ka ʻikepili pālua.

ʻōlelo ʻōlelo

ʻO ke ʻano syntax mea hoʻohana MySQL UNION:

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

hāmeʻa

• ʻōlelo1, ʻōlelo2, ... ʻōlelo_n: Kolu e kii.
• nā papa: ʻO ka papa ʻikepili e kiʻi.
• WHERE nā kūlana: ʻO ke koho, nā koho hulina.
• ʻOkoʻa: ʻO ke koho, wehe i ka ʻikepili pālua mai ka hoʻonohonoho hopena.Ua hoʻokaʻawale ka mea hoʻohana UNION i ka ʻikepili ma ka paʻamau, no laila ʻaʻohe hopena o ka mea hoʻololi DISTINCT i ka hopena.
• A pau: ʻO ke koho, hoʻihoʻi i nā pūʻulu hopena a pau, me nā kope.

hōkeo hōkeo

Ma kēia kumu aʻoaʻo, e hoʻohana mākou i ka waihona kikoʻī chenweiliang.

Eia ka ʻikepili mai ka papa "Websites":

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

Eia ka ʻikepili no ka "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 laʻana

Ke koho nei ka ʻōlelo SQL i nā mea a pau mai nā papa "Websites" a me "apps".ʻokoʻaʻāina (nā waiwai ʻokoʻa wale nō):

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

SQL UNION ALL laʻana

Hoʻohana ka ʻōlelo SQL ma lalo nei i ka UNION ALL e koho mai nā papa "Websites" a me "apps".nā mea āpauʻāina (ua loaʻa pū kekahi mau waiwai pālua):

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

SQL UNION ALL me WHERE

Hoʻohana ka ʻōlelo SQL ma lalo nei i ka UNION ALL e koho mai nā papa "Websites" a me "apps".nā mea āpauʻIkepili no Kina (CN) (me nā koina ʻelua):

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