Union kurongeka nemubvunzo syntax / chirevo chekushandiswa muMySQL dhatabhesi

MySQL databaseUnion kurongeka nemubvunzo syntax / chirevo chekushandiswa

MySQL UNION mushandisi

Ichi chidzidzo chinokuzivisa iwe kune syntax uye mienzaniso yeMySQL UNION opareta.

tsananguro

Iyo MySQL UNION opareta inoshandiswa kubatanidza mhedzisiro yezvirevo zviviri kana kupfuura SEZVA zvirevo kuita imwechete mhedzisiro seti.Multiple SELECT zvirevo zvinobvisa duplicate data.

girama

MySQL UNION opareta syntax fomati:

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

paramende

• kutaura1, kutaura2, ... kutaura_n: Column yekutora.
• matafura: Iyo data tafura yekutora.
• WHERE mamiriro: Optional, kutsvaga maitiro.
• DISTINCT: Sarudzo, bvisa duplicate data kubva pane zvabuda.Mushandisi weUNION akabvisa data nekukasira, saka DISTINCT modifier haina mhedzisiro pamhedzisiro.
• ZVESE: Sarudzo, inodzosa ese ese emhedzisiro, kusanganisira dzakapetwa.

demo database

Muchidzidzo ichi, tichashandisa chenweiliang sample database.

Heino data kubva pa "Webhusaiti" tafura:

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

Heino data ye "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 muenzaniso

Chirevo chinotevera cheSQL chinosarudza zvese kubva ku "Webhusaiti" uye "mapurogiramu" matafurazvakasiyananyika (yakasiyana chete tsika):

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

SQL UNION YESE muenzaniso

Chirevo chinotevera cheSQL chinoshandisa UNION ALL kusarudza kubva pa "Webhusaiti" uye "maapplication" matafurazvesenyika (ine zvakare ine duplicate values):

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

SQL UNION YESE ine WHERE

Chirevo chinotevera cheSQL chinoshandisa UNION ALL kusarudza kubva pa "Webhusaiti" uye "maapplication" matafurazveseData yeChina (CN) (zvakare ine duplicate values):

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