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Home php教程 php手冊 MYSQL到ORACLE程序遷移的注意事項(轉(zhuǎn)載)

MYSQL到ORACLE程序遷移的注意事項(轉(zhuǎn)載)

Jun 21, 2016 am 09:12 AM
mysql nbsp oracle select

mysql|oracle|程序

MYSQL到ORACLE程序遷移的注意事項?????????????

????????????????????????????????????2001-09


????有很多應(yīng)用項目, 剛起步的時候用MYSQL數(shù)據(jù)庫基本上能實現(xiàn)各種功能需求,隨著應(yīng)用用戶的增多,
數(shù)據(jù)量的增加,MYSQL漸漸地出現(xiàn)不堪重負的情況:連接很慢甚至宕機,于是就有把數(shù)據(jù)從MYSQL遷到
ORACLE的需求,應(yīng)用程序也要相應(yīng)做一些修改。本人總結(jié)出以下幾點注意事項,希望對大家有所幫助。

1. 自動增長的數(shù)據(jù)類型處理
????MYSQL有自動增長的數(shù)據(jù)類型,插入記錄時不用操作此字段,會自動獲得數(shù)據(jù)值。
ORACLE沒有自動增長的數(shù)據(jù)類型,需要建立一個自動增長的序列號,插入記錄時要把序列號的下一個
值賦于此字段。

????CREATE SEQUENCE 序列號的名稱 (最好是表名+序列號標記) INCREMENT BY 1??START??WITH??1
MAXVALUE??99999??CYCLE??NOCACHE;
????其中最大的值按字段的長度來定, 如果定義的自動增長的序列號 NUMBER(6) , 最大值為999999
????INSERT 語句插入這個字段值為: 序列號的名稱.NEXTVAL

2. 單引號的處理
????MYSQL里可以用雙引號包起字符串,ORACLE里只可以用單引號包起字符串。在插入和修改字符串
前必須做單引號的替換:把所有出現(xiàn)的一個單引號替換成兩個單引號。

3.??翻頁的SQL語句的處理
????MYSQL處理翻頁的SQL語句比較簡單,用LIMIT 開始位置, 記錄個數(shù);PHP里還可以用SEEK定位到結(jié)果
集的位置。
????ORACLE處理翻頁的SQL語句就比較繁瑣了。每個結(jié)果集只有一個ROWNUM字段標明它的位置, 并且只能
用ROWNUM80。
????以下是經(jīng)過分析后較好的兩種ORACLE翻頁SQL語句( ID是唯一關(guān)鍵字的字段名 ):
????語句一:
????SELECT ID, [FIELD_NAME,...] FROM TABLE_NAME WHERE ID IN ( SELECT ID FROM (SELECT
ROWNUM AS NUMROW, ID FROM TABLE_NAME WHERE 條件1 ORDER BY 條件2) WHERE NUMROW > 80 AND
NUMROW ??
????語句二:
????SELECT * FROM (( SELECT ROWNUM AS NUMROW, c.* from (select [FIELD_NAME,...] FROM
TABLE_NAME WHERE 條件1 ORDER BY 條件2) c) WHERE NUMROW > 80 AND NUMROW
4. 長字符串的處理
????長字符串的處理ORACLE也有它特殊的地方。INSERT和UPDATE時最大可操作的字符串長度小于等于
4000個單字節(jié), 如果要插入更長的字符串, 請考慮字段用CLOB類型,方法借用ORACLE里自帶的DBMS_LOB程序
包。插入修改記錄前一定要做進行非空和長度判斷,不能為空的字段值和超出長度字段值都應(yīng)該提出警告,
返回上次操作。

5.??日期字段的處理
????MYSQL日期字段分DATE和TIME兩種,ORACLE日期字段只有DATE,包含年月日時分秒信息,用當前數(shù)據(jù)庫
的系統(tǒng)時間為SYSDATE, 精確到秒,或者用字符串轉(zhuǎn)換成日期型函數(shù)TO_DATE(‘2001-08-01’,’YYYY-MM-DD’)
年-月-日 24小時:分鐘:秒 的格式Y(jié)YYY-MM-DD HH24:MI:SS TO_DATE()還有很多種日期格式, 可以參看
ORACLE DOC.
????日期型字段轉(zhuǎn)換成字符串函數(shù)TO_CHAR(‘2001-08-01’,’YYYY-MM-DD HH24:MI:SS’)

????日期字段的數(shù)學(xué)運算公式有很大的不同。
???????MYSQL找到離當前時間7天用
????DATE_FIELD_NAME > SUBDATE((NOW(),INTERVAL 7 DAY)
?????ORACLE找到離當前時間7天用
????DATE_FIELD_NAME >SYSDATE - 7;

6.??空字符的處理
????MYSQL的非空字段也有空的內(nèi)容,ORACLE里定義了非空字段就不容許有空的內(nèi)容。
????按MYSQL的NOT NULL來定義ORACLE表結(jié)構(gòu), 導(dǎo)數(shù)據(jù)的時候會產(chǎn)生錯誤。因此導(dǎo)數(shù)據(jù)時要對空字符進行判
斷,如果為NULL或空字符,需要把它改成一個空格的字符串。

7. 字符串的模糊比較
???MYSQL里用????????字段名 like '%字符串%'
???ORACLE里也可以用????字段名 like '%字符串%'????????但這種方法不能使用索引, 速度不快
???用字符串比較函數(shù)????????instr(字段名,'字符串')>0????????會得到更精確的查找結(jié)果????

8. 程序和函數(shù)里,操作數(shù)據(jù)庫的工作完成后請注意結(jié)果集和指針的釋放。


有興趣可以看MYSQL管理員指南????????????



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