Oracle updates another table with data from one of the tables

Set val = (exists (where tab1.id = tab2.id) 

In this way, the TAB2 part will not be updated to TAB1, but if the TAB2 is not the value of the part, TAB1 should be empty, then the last sentence removed, changed to

Set val = (where tab1.id = tab2.id)

Whether or not to remove the last sentence, once there is repetition, will be an error

A big guy's solution is to use the merge syntax

I still have a way to do this.

Set val = (exists (where tab1.id = tab2.id) 

If there are more than one also to replace, the values of the multiple should be the same (not surprisingly different to replace the case ...). , then it doesn't matter which one you use.

(By the way, what data types can be Max's)

If you don't need to be replaced, just remove the conditions.

Oracle updates another table with data from one of the tables