根据 parentId 和 min 值更新数据库中的记录

Question

I have a table like this.

ID | ParentId | Level | LevelStatus
1       1         5         NULL
2       1         6         NULL
3       2         4         NULL
4       2         2         NULL
5       3         2         NULL

I need to update the column LevelStatus with value 1 for each minimum level of the parentId. For example the lowest level for parentId 1 is Level 5 so it should only update that record, for parentId 2 it should update the record where level is 2.

I know how to select the right records. Something like this:

SELECT DISTINCT ParentId, MIN(Level) AS MinLevel
FROM TableA
GROUP BY ParentId

But don't know how to use it to write the update statement.

Answer 1

You can use a correlated subquery:

update tablea
    set levelstatus = 1
    where level = (select min(a2.level)
                   from tablea a2
                   where a2.parentid = a.parentid
                  );

This is standard SQL syntax and should work in every database . . . other than MySQL and MariaDB.