Removing duplicates based on matching column values with boolean indexing

After merging two DF’s I have the following dataset:

The y table contains multiple values for the left join variable (not included in table), resulting in multiple rows per unique DB_ID (string variable, not in df index).

The issue is that only one row is correct, where x_val and y_val match. I tried removing the duplicates with the following code:
df= df[~df['DB_ID'].duplicated() | combined['x_val'] != combined['y_val']]

This however doesn’t work. I am looking for a solution to achieve the following result:

>Solution :

Idea is compare both column for not equal, then sorting and reove duplicates by DB_ID:

df = (df.assign(new = df['x_val'].ne(df['y_val']))
        .sort_values(['DB_ID','new'])
        .drop_duplicates('DB_ID')
        .drop('new', axis=1))
print (df)
  DB_ID x_val y_val
1   x01   405   405
3   x02   308   308
4   x03   658   658
6   x04  None   658
8   x05   658   660
9   x06   660   660

If need equal NaNs or Nones use:

df = (df.assign(new = df['x_val'].fillna('same').ne(df['y_val'].fillna('same')))
        .sort_values(['DB_ID','new'])
        .drop_duplicates('DB_ID')
        .drop('new', axis=1))