MySQL winter vacation self-study 2022 12 (3)

--  String function 

-- 1, Get the number of string characters 
select char_length('hello '); #6 The space is also called 
select char_length(' how are you '); #3  Chinese characters count as 
-- charactr_length  and char_length  The same function 
-- length  Take the length , The units returned are bytes 
select length('hello '); #6
select length(' how are you '); #9 UTF-8 In the encoding , Chinese characters take up three bytes 

-- 2, String merge 
select concat('hello','world','scx');
--  Specify delimiters for string merging 
select concat_ws('-','hello','world');

-- 3, Returns the position where the string first appears in the list 
select field('aaa','aaa','bbb','ccc'); #1
select field('bbb','aaa','bbb','ccc'); #2
select field('ddd','aaa','bbb','ccc'); #0, Not found 
 
--  4, Remove the space to the left of the string 
select ltrim('  abcd         ');
--  Remove the space on the right 
select rtrim('  abcd         ');
--  Remove the blanks at both ends , The middle string cannot be removed 
select trim('  abcd         ');

-- 5, String interception 
select mid('helloworld',2,3);# Intercept three characters from the second position , The length is 3

-- 6, Get string a In string b Where in , Which one you see first returns which 
select position('abc' in 'helloabcworld');#6
select position('abc' in 'habcelloabcworld');#2

-- 7, String substitution , If I have two aaa Replace them all 
select replace('helloaaaworld','aaa','bbb');#hellobbbworld
select replace('aaahelloaaaworld','aaa','bbb');#bbbhellobbbworld
-- 8, String inversion 
select reverse('hello');#olleh