Sql Server substring(expression, start, length)函数.docx

SqlServersubstring函数[sql]view plaincopyprint?Syntax?for?SUBSTRING:????SUBSTRING(expression,?start,?length)??Syntax for SUBSTRING: SUBSTRING(expression, start, length)expression? ? ? ? 字符串、二进制字符串、文本、图像、列或包含列的表达式。请勿使用包含聚合函数的表达式。start? ? ? ? 整数或可以隐式转换为int的表达式，指定子字符串的开始位置。length? ? ? ? 整数或可以隐式转换为int的表达式，指定子字符串的长度。例子：1、起始位置为0，截取长度为3[sql]view plaincopyprint?select?substring(DWMC,0,3)?as?Sub,DWMC?as?DWMC?from?DW?where?DWNM?select substring(DWMC,0,3) as Sub,DWMC as DWMC from DW where DWNM果：2、起始位置为1，截取长度为3[sql]view plaincopyprint?select?substring(DWMC,1,3)?as?Sub,DWMC?as?DWMC?from?DW?where?DWNM?select substring(DWMC,1,3) as Sub,DWMC as DWMC from DW where DWNM果：3、起始位置为-1，截取长度为3[sql]view plaincopyprint?select?substring(DWMC,-1,3)?as?Sub,DWMC?as?DWMC?from?DW?where?DWNM?select substring(DWMC,-1,3) as Sub,DWMC as DWMC from DW where DWNM果：4、起始位置为-2，截取长度为3[sql]view plaincopyprint?select?substring(DWMC,-2,3)?as?Sub,DWMC?as?DWMC?from?DW?where?DWNM?select substring(DWMC,-2,3) as Sub,DWMC as DWMC from DW where DWNM果：5、起始位置为-9，截取长度为3[sql]view plaincopyprint?select?substring(DWMC,-9,3)?as?Sub,DWMC?as?DWMC?from?DW?where?DWNM?select substring(DWMC,-9,3) as Sub,DWMC as DWMC from DW where DWNM果：? ? ? ? 通过上面的例子，可以看出substring的截取，类似于X坐标上截取绝对长度，而对于字符串而言，负数及零的位置都是空，真正有数的位置是从1开始的！