Update the data of another table using the data of one table in Oracle

Oracle has the following two tables: update the val value of the row with the same id value in Table tab1 and that in Table tab2 to the val value in table 2.
Select * from tab1;

Select * from tab2

The most common mistake is: update tab1 set val = (select val from tab2 where tab1.id = tab2.id );
The updated result is: select * from tab1, which has rows in tab1. If no corresponding row exists in tab2, the value is updated to null.

Corrected to: update tab1 set val = (select val from tab2 where tab1.id = tab2.id)
Where exists (select 1 from tab2 where tab1.id = tab2.id)
However, if multiple entries in tab2 correspond to one entry in tab1, an error occurs.
The best way is to use merge Syntax:

1. MergeIntoTab1
2. Using tab2
3. On(Tab1.id = tab2.id)
4. WhenMatchedThen
5. Update SetTab1.val = tab2.val

Similarly, an error occurs if multiple entries in tab2 correspond to one entry in tab1: ORA-30926: unable to get a stable set of rows in the source tables
For example, insert an insert into tab2 values (2, 'xxxx') in tab2 ')
This error can be avoided by filtering repeated records in the subquery of using. For merge future edition:

1. MergeIntoTab1
2. Using (Select*FROMTab2 XWHEREX. ROWID =
3. (SELECT MAX(Y. ROWID)FROMTab2 YWHEREX. ID = Y. ID) tab2
4. On(Tab1.id = tab2.id)
5. WhenMatchedThen
6. Update SetTab1.val = tab2.val

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