/* 获取字符串长度函数：length（char）
select bookname ,length(bookname) from bookinfo; */
/* 去除字符串首尾指定字符函数：trim([leading|trailing|both] [trim_character From] trim_source)
select b_price2,length(b_price2),length(trim(b_price2)) from books5;
leading 前缀字符
trailing 后缀字符
both 前后
trim_character From 要删除的指定字符串
select trim(trailing 3 from trim(leading '1' from trim(b_price2))) from books5;
select trim(trailing 3 from trim(leading '1' from trim(both ‘ ’ from b_price2))) from books5;*/
/* 字符串截取函数：{[substr]|[substrb]|[substrc]|[substr2]|[substr4]}(char,position[,substring_length])
substr 按字符截取，单位字符
substrb 按字节，单位字节
substrc unicode字符为单位
substr2 ucs2代码点为单位
substr4 ucs4代码点为单位
char 参数，原始字符串
position 开始位置，初始值1，-1表示从右侧开始
substring_length 截取的长度
select substr4(b_name,1,5) from books;
select substr4(b_name,-1,5) from books; */
/* 字符串连接函数：concat()
select concat(b_id,b_name) from books;
select concat(b_id,‘__’) from books;
select concat(‘__’,b_id) from books;
select (B_NAME||'__'||B_NAME) from books; */
/* 小写字母转大写函数：upper(char)
select upper(b_name) from books; */
/* 大写字母转小写函数：lower(char)
select lower(b_name) from books; */
/* 检索字符串函数：{[instr]|[instrb]|[instrc]|[instr2]|[instr4]}(string,substring[,position[,occurrence]])
instr 检索某个字符串在另一个字符串中出现的位置，以字符为单位,范围字符的位置
instrb 返回字节的位置
string 被检索的字符串
substring 检索字符串
position 开始位置，默认1
occurrence substring第几次出现,默认1
select b_name,instr(b_name,'basic') from books;
select b_name,instr(b_name,'basic',1,1) from books;
select b_name,instr('abcabdwe','b') from dual; */