MySQL converts comma separated attribute field data from column to row

Mysql Convert comma separated attribute fields to row data

Mysql Convert comma separated attribute fields to row data .

• scene ：

At development time , We will design the database table according to the requirements . Sometimes when designing data tables, we can't conform to the three paradigms , Complexity of cause scenario , If we follow the three paradigms all the time , It will increase our development . Sometimes we use commas to store some in an attribute value id It's worth waiting for . When querying, you need to convert attributes into rows .

• data ：

• solve ：

select a.*,SUBSTRING_INDEX(SUBSTRING_INDEX(a.content,',',b.id),',',-1) content
from temp a 
join temp b
where b.id <= LENGTH(a.content)-LENGTH(REPLACE(a.content,',',''))+1 

• result ：
  
• Function analysis
  SUBSTRING_INDEX ： Get separator after separation , Get the string according to the last parameter index , Negative numbers are reciprocal
  LENGTH : character string length
  REPLACE ： Replace string

summary ：
join The table needs to find a table whose attribute is 1 Start incremental . They usually use mysql.help_topic This table , But the data in this table id It is limited. , Even in some cases, you don't have permission to access the table .