MySQL視圖介紹

{"type":"doc","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"前言："},{"type":"text","text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"在MySQL中，視圖可能是我們最常用的數據庫對象之一了。那麼你知道視圖和表的區別嗎？你知道創建及使用視圖要注意哪些點嗎？可能很多人對視圖只是一知半解，想詳細瞭解視圖的同學看過來喲，本篇文章會詳細介紹視圖的概念、創建及使用方法。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"1.視圖定義及簡單介紹"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖是基於 SQL 語句的結果集的可視化的表，即視圖是一個虛擬存在的表，可以包含表的全部或者部分記錄，也可以由一個表或者多個表來創建。使用視圖就可以不用看到數據表中的所有數據，而是隻想得到所需的數據。當我們創建一個視圖的時候，實際上是在數據庫裏執行了SELECT語句，SELECT語句包含了字段名稱、函數、運算符，來給用戶顯示數據。 "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖的數據是依賴原來表中的數據的，所以原來的表的數據發生了改變，那麼顯示的視圖的數據也會跟着改變，例如向數據表中插入數據，那麼在查看視圖的時候，會發現視圖中也被插入了同樣的數據。視圖實際上是由預定義的查詢形式的表所組成的。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"2.視圖創建及使用方法"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"創建視圖標準語法："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"sql"},"content":[{"type":"text","text":"CREATE\n [OR REPLACE]\n [ALGORITHM = {UNDEFINED | MERGE | TEMPTABLE}]\n [DEFINER = user]\n [SQL SECURITY { DEFINER | INVOKER }]\n VIEW view_name [(column_list)]\n AS select_statement\n [WITH [CASCADED | LOCAL] CHECK OPTION]"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"語法解讀："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1）OR REPLACE：表示替換已有視圖，如果該視圖不存在，則CREATE OR REPLACE VIEW與CREATE VIEW相同。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2）ALGORITHM：表示視圖選擇算法，默認算法是UNDEFINED(未定義的)：MySQL自動選擇要使用的算法 ；merge合併；temptable臨時表，一般該參數不顯式指定。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3）DEFINER：指出誰是視圖的創建者或定義者，如果不指定該選項，則創建視圖的用戶就是定義者。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"4）SQL SECURITY：SQL安全性，默認爲DEFINER。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"5）select_statement：表示select語句，可以從基表或其他視圖中進行選擇。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"6）WITH CHECK OPTION：表示視圖在更新時保證約束，默認是CASCADED。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"其實我們日常創建視圖時，無需指定每個參數，一般情況下，建議這樣創建視圖："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"sql"},"content":[{"type":"text","text":"create view [(column_list)]\nas select語句\nwith check option;"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面給出幾個具體創建示例："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"codeblock","attrs":{"lang":"sql"},"content":[{"type":"text","text":"# 單表視圖\nmysql> create view v_F_players(編號,名字,性別,電話)\n -> as\n -> select PLAYERNO,NAME,SEX,PHONENO from PLAYERS\n -> where SEX='F'\n -> with check option;\nQuery OK, 0 rows affected (0.00 sec)\n\nmysql> desc v_F_players;\n+--------+----------+------+-----+---------+-------+\n| Field | Type | Null | Key | Default | Extra |\n+--------+----------+------+-----+---------+-------+\n| 編號 | int(11) | NO | | NULL | |\n| 名字 | char(15) | NO | | NULL | |\n| 性別 | char(1) | NO | | NULL | |\n| 電話 | char(13) | YES | | NULL | |\n+--------+----------+------+-----+---------+-------+\n4 rows in set (0.00 sec)\n\nmysql> select * from v_F_players;\n+--------+-----------+--------+------------+\n| 編號 | 名字 | 性別 | 電話 |\n+--------+-----------+--------+------------+\n| 8 | Newcastle | F | 070-458458 |\n| 27 | Collins | F | 079-234857 |\n| 28 | Collins | F | 010-659599 |\n| 104 | Moorman | F | 079-987571 |\n| 112 | Bailey | F | 010-548745 |\n+--------+-----------+--------+------------+\n5 rows in set (0.02 sec)\n\n# 多表視圖\nmysql> create view v_match\n -> as \n -> select a.PLAYERNO,a.NAME,MATCHNO,WON,LOST,c.TEAMNO,c.DIVISION\n -> from \n -> PLAYERS a,MATCHES b,TEAMS c\n -> where a.PLAYERNO=b.PLAYERNO and b.TEAMNO=c.TEAMNO;\nQuery OK, 0 rows affected (0.03 sec)\n\nmysql> select * from v_match;\n+----------+-----------+---------+-----+------+--------+----------+\n| PLAYERNO | NAME | MATCHNO | WON | LOST | TEAMNO | DIVISION |\n+----------+-----------+---------+-----+------+--------+----------+\n| 6 | Parmenter | 1 | 3 | 1 | 1 | first |\n| 44 | Baker | 4 | 3 | 2 | 1 | first |\n| 83 | Hope | 5 | 0 | 3 | 1 | first |\n| 112 | Bailey | 12 | 1 | 3 | 2 | second |\n| 8 | Newcastle | 13 | 0 | 3 | 2 | second |\n+----------+-----------+---------+-----+------+--------+----------+\n5 rows in set (0.04 sec)"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖在使用時和基礎表一樣，比如我們可以使用 select "},{"type":"text","marks":[{"type":"italic"}],"text":" from view_name 或 select "},{"type":"text","text":" from view_name where ... ，視圖可以將我們不需要的數據過濾掉，將相關的列名用我們自定義的列名替換。視圖作爲一個訪問接口，不管基表的表結構和表名有多複雜。一般情況下視圖只用於查詢，視圖本身沒有數據，因此對視圖進行的dml操作最終都體現在基表中，對視圖進行delete、update、insert操作，原表同樣會更新，drop視圖原表不會變，視圖不可以truncate。但是一般情況下我們要避免更新視圖，dml操作可以直接對原表進行更新。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"heading","attrs":{"align":null,"level":4},"content":[{"type":"text","text":"3.視圖相關最佳實踐"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"下面簡單介紹下視圖的優點，通過這些優點我們很容易總結出視圖的適用場景。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"1）簡單：使用視圖的用戶完全不需要關心後面對應的表的結構、關聯條件和篩選條件，對用戶來說已經是過濾好的複合條件的結果集。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"2）安全：使用視圖的用戶只能訪問他們被允許查詢的結果集，對錶的權限管理並不能限制到某個行某個列，但是通過視圖就可以簡單的實現。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"3）數據獨立：一旦視圖的結構確定了，可以屏蔽表結構變化對用戶的影響，源表增加列對視圖沒有影響；源表修改列名，則可以通過修改視圖來解決，不會造成對訪問者的影響。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"總而言之，使用視圖的大部分情況是爲了保障數據安全性，提高查詢效率。比如說我們經常用到幾個表的關聯結果，那麼我們就可以使用視圖來處理，或者說第三方程序需要調用我們的業務庫，可以按需創建視圖給第三方程序查詢。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"對於日常使用及維護視圖的過程中，個人總結出以下幾點實踐，可供參考："}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"bulletedlist","content":[{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖命名建議統一前綴，比如以v"},{"type":"text","marks":[{"type":"italic"}],"text":"或view"},{"type":"text","text":"開頭，便於識別。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"SQL SECURITY使用默認的DEFINER，表示已視圖定義者的權限去查詢視圖。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖定義者建議使用相關程序用戶。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖不要關聯太多的表，造成數據冗餘。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"查詢視圖時要附帶條件，不建議每次都查詢出所有數據。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖遷移要注意在新環境有該視圖的定義者用戶。"}]}]},{"type":"listitem","content":[{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"不要直接更新視圖中的數據，視圖只作查詢。"}]}]}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","marks":[{"type":"strong"}],"text":"總結："},{"type":"text","text":" "}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null},"content":[{"type":"text","text":"視圖在MySQL中經常會用到，本篇文章介紹了視圖的概念以及創建方法，延伸而來，後續又講述了視圖的使用場景及優點。可能在使用時感覺不出視圖和表的區別，其實這裏面的門道還有很多，在這裏建議視圖只作查詢使用，按照規範來，視圖會帶來很大的便捷。希望這篇文章對你有幫助。"}]},{"type":"paragraph","attrs":{"indent":0,"number":0,"align":null,"origin":null}}]}