Te raupapa uniana ma te uiui wetereo/whakamahi korero i roto i te paataka raraunga MySQL

pātengi raraunga MySQLRaupapa uniana ma te wetereo uiui/whakamahi korero

MySQL Kaiwhakahaere UNION

Ma tenei akoranga e whakaatu ki a koe te wetereo me nga tauira o te kaiwhakahaere MySQL UNION.

whakaahuatanga

Ka whakamahia te kaiwhakahaere MySQL UNION ki te whakakotahi i nga hua o nga korero SELECT e rua, neke atu ranei ki te huinga hua kotahi.He maha nga korero SELECT ka tango i nga raraunga taarua.

wetereo

Hōputu wetereo kaiwhakahaere MySQL UNION:

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

Parapeta

• whakapuaki1, whakapuaki2, ... whakapuaki_n: Tīwae hei tiki.
• tepu: Ko te ripanga raraunga hei tiki.
• Ko nga tikanga: Kōwhiringa, paearu rapu.
• WHAKAMAHI: Ka taea, tangohia nga raraunga taarua mai i te huinga hua.Kua whakakorehia e te kaiwhakahaere UNION nga raraunga ma te taunoa, no reira karekau he paanga o te whakakē DISTINCT ki te hua.
• KATOA: Ka taea, ka whakahoki i nga huinga hua katoa, tae atu ki nga taarua.

pātengi raraunga demo

I roto i tenei akoranga, ka whakamahia e matou te tauira raraunga chenweiliang.

Anei nga raraunga mai i te ripanga "Paetukutuku":

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

Anei nga raraunga mo te "taupānga" 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 tauira

Ko te tauākī SQL e whai ake nei ka tohua katoa mai i nga ripanga "Paetukutuku" me "taupānga".rerekēwhenua (nga uara motuhake anake):

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

SQL UNION KATOA tauira

Ko te tauākī SQL e whai ake nei e whakamahi ana i te UNION KATOA hei kowhiri mai i nga ripanga "Paetukutuku" me nga "taupānga".katoawhenua (he uara taarua ano hoki):

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

SQL UNION KATOA me WHERE

Ko te tauākī SQL e whai ake nei e whakamahi ana i te UNION KATOA hei kowhiri mai i nga ripanga "Paetukutuku" me nga "taupānga".katoaRaraunga mo Haina (CN) (me nga uara taarua):

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