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Home Database Mysql Tutorial Oracle數(shù)據(jù)庫中的字符處理技巧總結(jié)

Oracle數(shù)據(jù)庫中的字符處理技巧總結(jié)

Jun 07, 2016 pm 04:54 PM
oracle database

在數(shù)據(jù)庫開發(fā)與維護(hù)中,數(shù)據(jù)庫管理員接觸最多的數(shù)據(jù)類型就是字符類型了,包括字符串、日期類型的字符串等等。在Oracle數(shù)據(jù)庫

  在數(shù)據(jù)庫開發(fā)與維護(hù)中,數(shù)據(jù)庫管理員接觸最多的數(shù)據(jù)類型就是字符類型了,包括字符串、日期類型的字符串等等。在Oracle數(shù)據(jù)庫中為了幫助數(shù)據(jù)庫管理員能夠以最快的方式處理這些字符類型的數(shù)據(jù),提供了許多有用的函數(shù)或者工具。筆者今天就談?wù)勗贠racle數(shù)據(jù)庫中處理字符串的經(jīng)驗與心得。

  一、去掉尾部的空格字符。

  有時候在查詢或者進(jìn)行其他處理的時候,需要把字符串尾部的空格字符去掉。如有時候應(yīng)用軟件設(shè)計的不合理,會把空格字符保存在數(shù)據(jù)庫中。如在輸入產(chǎn)品品號的時候,用戶不小心,把“DT001”輸成了“DT001 ”。如果應(yīng)用程序在設(shè)計的時候,能夠自動把尾部的空格去掉然后在保存到數(shù)據(jù)庫中能夠就萬無一失了。但是不少的應(yīng)用軟件在開發(fā)的時候沒有如此設(shè)計。這就給后續(xù)的處理帶來了很多的麻煩。因為利用Where語句來查找記錄的時候,“DT001”(最后不帶空格)與“DT001 ”(最后帶一個空格)兩個是不同的條件。如果想利用這個條件來進(jìn)行數(shù)據(jù)更新、查詢等等,就會遇到問題。為此在寫相關(guān)的Update或者Select語句的時候,可能需要把后面的空格符號去掉。為此在Oracle數(shù)據(jù)庫中,有很多種解決方式。如數(shù)據(jù)庫管理員可以使用Ltrim函數(shù)來實現(xiàn)。這個函數(shù)的格式為Ltrim[c1,c2]。其作用是去掉C1左邊所包含的C2種的任何字符。當(dāng)遇到不是C2種的字符串時結(jié)束,然后返回剩余的字符串。如果把C2字符串設(shè)置為空格符號(默認(rèn)情況下就是空格),那么就可以把DT001后面的空格符號去掉了。

  二、在頭部自動進(jìn)行填充。

  有時候可能數(shù)據(jù)庫設(shè)計的時候,考慮的不夠周到,導(dǎo)致某些字段不夠大。在對數(shù)據(jù)庫進(jìn)行升級的時候,需要調(diào)整相關(guān)的字段。此時就可能需要對某個字段的頭部進(jìn)行填充,以達(dá)到數(shù)據(jù)一致性的要求。如現(xiàn)在有個ERP系統(tǒng),其需要用到一張產(chǎn)品信息的表,其中有一個產(chǎn)品編號字段。剛開始在設(shè)計產(chǎn)品編碼的時候,設(shè)計的長度不夠,如只設(shè)置了5位。隨著企業(yè)產(chǎn)品記錄的增多,需要對這個編碼的內(nèi)容進(jìn)行擴展。如產(chǎn)品信息屬于包裝材料類的,需要在原來產(chǎn)品編號的頭部加入一個字符B;如產(chǎn)品信息屬于客供品的,則需要在原來產(chǎn)品編號的頭部加入一個字符C;如產(chǎn)品信息屬于輔助材料的,則在原來的產(chǎn)品編號前面加入一個字符F;等等。此時該如何實現(xiàn)這個需求呢?難道要一個個去修改嗎?現(xiàn)在這手工修改的工作量比較大,而且容易出錯,這個方法不可取。其實在Oracle數(shù)據(jù)庫系統(tǒng)中提供了一個單行字符函數(shù),可以幫助數(shù)據(jù)庫管理員與企業(yè)來解決這個問題。這個函數(shù)就是RPAD函數(shù)。這個命令的格式為RPAD(C1,N,C2)。這個函數(shù)的意識是在C1的右邊填充字符C2,直到字符串的總長度滿足N。默認(rèn)情況下C2的值為空格,用戶可以根據(jù)自己的需要設(shè)置這個值。如果C1的長度比N要大,則會截取C1右邊的N個字符?,F(xiàn)在如果要實現(xiàn)上面這個需求,則只需要設(shè)置函數(shù)RPAD(產(chǎn)品編號,6,F(xiàn))即可。由于原來的產(chǎn)品編號為5位,現(xiàn)在需要為輔助信息的產(chǎn)品編號前面加入一個字符F,修改后的總長度變?yōu)?位。不過在使用這個函數(shù)的話,往往需要利用Where條件語句進(jìn)行限制。

  現(xiàn)在這個函數(shù)還可以里用實現(xiàn)字符串的截取。如還是這個產(chǎn)品編號,其前面一位表示產(chǎn)品的種類。此時數(shù)據(jù)庫管理員就可以利用RPAD(產(chǎn)品編號,1)來截取產(chǎn)品編號的第一位字符(這里產(chǎn)品編號的長度比1要大,則會截取產(chǎn)品右邊的1個字符,即產(chǎn)品類別標(biāo)示碼)。這在報表設(shè)計的時候也非常有用,有利于簡化報表的顯示。

  三、字符大小寫的控制。

  在做報表的時候,我們可能需要對字符串的現(xiàn)實格式進(jìn)行控制,如大小寫的顯示格式。另外,在進(jìn)行數(shù)據(jù)庫移植的時候,可能以前的收入大小寫不規(guī)范。數(shù)據(jù)庫管理員需要采用一定的規(guī)則來規(guī)范移植后的數(shù)據(jù)庫字符串書寫規(guī)范。為了簡化這些需求的實現(xiàn)方式,在Oracle數(shù)據(jù)庫中也提供了一些工具來解決這些問題。

  如以前在輸入產(chǎn)品編號的時,可能大小寫不區(qū)分。而在前臺應(yīng)用程序中也沒有進(jìn)行這方面的控制?,F(xiàn)在用戶希望所有的產(chǎn)品編號都為大寫,,需要把原先是小寫的產(chǎn)品編號全部轉(zhuǎn)換成大寫。此時如果產(chǎn)品數(shù)量比較多的話,顯然利用手工修改的方式會增加工作量。如果編寫一個程序來實現(xiàn)的話,又太復(fù)雜,其實我們可以借鑒Oracle數(shù)據(jù)庫提供的字符串處理函數(shù)來實現(xiàn)。在單行字符函數(shù)集中,有一個函數(shù)UPPER,它的作用就是將全部字符串都改寫為大寫并返回。為此我們可以利用一個子查詢或者借助視圖的幫助,把所有產(chǎn)品編號中,如果含有小寫字符的產(chǎn)品編號都更新為大寫。如果原來就是大寫的,就保持原樣(而不是說原來大寫的變小寫,原來小寫的變大寫)。同理,既然小寫可以變大寫,那么大寫也就可以變?yōu)樾?。利用單行字符串函?shù)LOWER,就可以把全部字符串改為小寫輸出(把大寫字母改為小寫,而小寫字符保持不變)。

  另外一個大小寫的控制原則比較復(fù)雜,如對于一些英文地址或者英文名字之類的字符串,需要首個字母大寫,而其他字符小寫。這個實現(xiàn)起來就有一定的難度。還好在Oracle數(shù)據(jù)庫中提供了一個現(xiàn)成的解決方法,即利用Initchar函數(shù)來實現(xiàn)。這個函數(shù)的功能是將某個字段中每個單詞的首字符轉(zhuǎn)換為大小,其他字符都是小寫的字符串。通常情況下,這個字段之間的單詞可以利用空格、控制字符或則標(biāo)點符號來表示??梢娡ㄟ^這個三個大小寫字符串控制函數(shù),可以優(yōu)化字符串的顯示格式,讓其顯示更加的規(guī)范。而結(jié)合Update語句的話,還可以成批的在數(shù)據(jù)庫中進(jìn)行更新,讓其保存的數(shù)據(jù)也符合規(guī)范化的要求。

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