Record common functions in MySQL at work

find_in_set() function
Determine whether a value is included
and in The difference between , see https://blog.csdn.net/wangqing84411433/article/details/116518197
Merge the above values into one cell , use CONCAT(str1,str2,…)
The return result is the string generated by the connection parameter . If any parameter is NULL , The return value is NULL.

For merging multiple statement result sets
union and union all function

difference
Use UNION when ,MySQL Records with duplicate query results will be deleted

Use UNION ALL ,MySQL All records of the query results will be returned
Reference resources

https://www.zhihu.com/tardis/sogou/art/368409836