ORACLE replace和translate函数详解
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简要比较：
replace：字符串级别的代替
如： SELECT REPLACE( 'acdd ',' cd ef ') FROMdual; →aefd translate：字符级别的代替 如： TRANSLATE( acdd FROMdual; →aeff 分别详解： replace: 语法：REPLACE ( char,search_string [,replacement_string] ) REPLACE returns char with every occurrence of search_string replaced with replacement_string. If replacement_string is omitted or null,then all occurrences of search_string are removed. If search_string is null,then char is returned. 解释：repalce中，每个search_string都被replacement_string所代替。 select replace( fromdual;→aefd 如果replacement_string为空或为NULL,那么所有的search_string都被移除。 '') fromdual;→ad 如果search_string为null,那么就返回原来的char。 '',255);">fromdual;→acddfromdual;→acdd(也是两者都为空的情况) Both search_string and replacement_string,as well as char,can be any of the datatypes CHAR,VARCHAR2,NCHAR,NVARCHAR2,CLOB,or NCLOB. The string returned is of VARCHAR2 datatype and is in the same character set as char. 解释：这段指明了可以用的数据类型. This function provides functionality related to that provided by the TRANSLATE function.TRANSLATE provides single-character,one-to-one substitution. REPLACE lets you substitute one string for another as well as to remove character strings. 解释：红色部分也是replace和translate的区别。 translate: 语法：TRANSLATE ( 'char','from_string','to_string' ) TRANSLATE returns char with all occurrences of each character in from_string replaced by its corresponding character in to_string. Characters in char that are not in from_string are not replaced. The argument from_string can contain more characters than to_string. In this case,the extra characters at the end of from_string have no corresponding characters in to_string. If these extra characters appear in char,then they are removed from the return value.You cannot use an empty string for to_string to remove all characters in from_string from the return value. Oracle interprets the empty string as null,and if this function has a null argument,then it returns null. 解释：Translate中，每个from_string中的字符被to_string中相应的字符所代替。 selecttranslate( fromdual;→aeff如果from_string比to_string长，那么from_string中多余的字符将被移除。 acd fromdual;→ef(a由e代替，c由f代替,d就被移除)cda fromdual;→eff(c由e代替，d由f代替，a就被移除) 如果to_string为空，或者两者都为空，那么返回char也为空。所以to_string不能为空。 fromdual;→(空)fromdual;→(空) 实战： 如何判断一个字符串是否是数字？ 解：先转换：由于to_string不能为空，我们巧用#号代替 abc123 #1234567890. # fromdual;→abc from_string中的#被to_string中的#代替，但char中又没有#字符，所以通过这一步躲开了to_string必须不为空的规则。然后后面的数字以及小数点都转换为空，于是原来的字符串中只留下abc三个字符。 转换好后，用nvl2判断即可： selectnvl2(translate( '),0);">字符串 数字 fromdual;→字符串nvl2的作用就是，NVL2 (expr1,expr2,expr3) ->expr1不为NULL，返回expr2；为NULL，返回expr3。这样我们就可以判断一个字符串是否是数字了!解毕! （编辑：李大同） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |