ORACLE PL/SQL 字符串函数、数学函数、日期函数
--【字符串函数】
--字符串截取substr(字段名，起始点,个数)
select Name,substr(Name,2,4),substr(Name,0,3),substr(Name,-2,3),substr(Name,-2,1) from t1;
--字符串从前面取三个(0开始)
select Name,substr(Name,0,3) from t1;
--字符串从后面取三个
select Name,substr(Name,-3,3),length(Name) 串长度 from t1;
SELECT ASCII('A'),ASCII('B') from dual;
select CHR(100),CHR(80) from dual;
select CONCAT(CHR(65),CONCAT(CHR(67),CHR(98))) from dual;
select CHR(65)||CHR(66)||CHR(76) from dual;
--将每个单词的第一个字母大写其它字母小写返回。
select INITCAP('substr,abc,substring') from dual;
--返回i在MISSISSIPPI中第3次出现的位置，
select INSTR('Mississippi','i',5,3) from dual;
select INSTR('Mississippi','i',-2,3) from dual;
--返回的是字节
select INSTRB('Mississippi','i',5,3) from dual;
select INSTRB('Mississippi','i',-2,3) from dual;
--长度
select length('WHO ARE YOU') from dual;
select nvl(null,'空') from dual;
--小写
select lower('WHo are You') from dual;
--LPAD左侧用字符串补足到一定长度
select LPAD('DFSDf................',9,'WHO') from dual;
select LPAD('DFSD',9,'WHO') from dual;
select LPAD('DFSD',9,'') from dual;
select LPAD('DFSD',length('DFSD')+length('WHO......'),'WHO......') from dual;
--把最左边的字符去掉，使其第一个字符不在其中
select ltrim('Mississippi','Mis') from dual;
select ltrim('Mississippi','miD') from dual;
--RPAD右侧用字符串补足到一定长度
select RPAD('DFSDf................',9,'WHO') from dual;
select RPAD('DFSD',9,'WHO') from dual;
select RPAD('DFSD',9,'') from dual;
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