Reprinted from https://www.cnblogs.com/lijiageng/p/6511334.html
Function:
1. Intercept the string
left (str, length) from
the left Description: left (intercepted field, intercepted length)
Example: select left (content, 200) as abstract from my_content_t
2. Intercept the string
right (str, length) from
the right Description: right (intercepted field, intercepted length)
Example: select right (content, 200) as abstract from my_content_t
3. Intercept string
substring (str, pos)
substring (str, pos, length)
description: substring (intercepted field, intercepted from the first position)
substring (intercepted field, intercepted from the first position, intercepted length)
Example: select substring(content,5) as abstract from my_content_t
select substring(content,5,200) as abstract from my_content_t
(Note: if the number of digits is negative, such as -5, it is from the last number to the end of the string or intercepted length)
4. Intercept string
substring_index (str, delim, count) by keyword
Description: substring_index (intercepted field, keyword, number of occurrences of keyword)
Example: select substring_index ("blog.jb51.net", ".", 2) as abstract from my_content_t
result: blog.jb51
(Note: If the number of times the keyword appears is negative, such as -2, it will count down from the back to the end of the string)
Function introduction:
SUBSTRING(str,pos) , SUBSTRING(str FROM pos) SUBSTRING(str,pos,len) , SUBSTRING(str FROM pos FOR len)
The format without the len parameter returns a substring from the string str , starting at position pos . The format with the len parameter returns a substring of the same length as len characters from the string str , starting at position pos . The format using FROM is standard SQL syntax. It is also possible to use a negative value for pos . If so, the position of the substring starts at the pos character at the end of the string, not at the beginning of the string. A negative value for pos can be used in functions of the following format .