加入 oracle sql 更新

Question

I want to update a column of a table1 but I should update only records where conditions are true in another table something like this, but I don't know how to implement this purpose in Oracle SQL

update table1
join table2 on table1.msg_id = table2.id
set table1.index = table1.index-1
where table1.index > 10 and table2.type = 'myType'

Answer 1

I would write this as an exists subquery in any database:

update table1 t1
    set index = t1.index - 1
where table1.index > 10 and
      exists (select 1
              from table2
              where t2.id = t1.msg_id and
                    t2.type = 'myType'
             );

The join sort of implies that you are going to use data from table2 in the update of table1 . Instead, you simply want to change a value in a row when a particular condition is met.

Answer 2

Oracle does not support this syntax (sigh).

For your use case, you could use a not exists condition with a correlated subquery instead:

update table1
set table1.index = table1.index - 1
where 
    table1.index > 10
    and exists (
        select 1 from table2 where table1.msg_id = table2.id and table2.type = 'mytype'
    )

Note: make your live easier, do not use index for a column name. This is a reserved work in pretty much all RDBMS.