sql - Insert NULL if value matches the value of another column -

lets have table : "mytable" , have 2 columns in : "val" , "val_new".

now want insert new value "val_new" if values equal('val' , 'val_new') want insert null instead.

---------------------- | id | val | val_new | ---------------------- | 1  |  5  |  null   | ---------------------- | 2  |  6  |  null   | ---------------------- 

lets have table example.

now :

update mytable mt set mt.val_new = '5' mt.id = '1'; 

i want value of val_new remain null or updated null instead of '5'.

edit: want update existing values not inserting new rows.

you need not have insert record rather have update existing one. if run insert command new record created. table have

---------------- |val | val_new | ---------------- | 5  |  null   | ---------------- | 6  |  null   | ---------------- |    |         | <-- if val = val_new ---------------- |    |   6     | <==if val<> val_new. 

i guess dont need output. best option update columns.

you can use case statement,

update <yourtable> set val_new =case                  when  val_new= val                    null                 else val_new              end