MySQL Knowledge point collation

1.CONCAT (STR1,STR2,...) returns the string that results from the connection parameter. If any one of the arguments is NULL, the return value is null.
2.group_concat (column name) indicates that the value of a field is incremented by a specified character, and the default delimiter is a comma
3.find_in_set (a,alist) queries the value of field A in Alist, such as: Find_in_set (ID, (#)) equivalent to ID in (A/b) This is an object with a query ID of zero
Second usage: find_in_set ("1", ID) Query ID contains "1" Object

MySQL Knowledge point collation