SQL Server：添加增量值（不是身份）

Question

I have a table and I want to insert some rows. There is a column num which is not identity. When the insertion of new rows takes place I want the num value to be incremented by 1 starting from the highest existing value. Here is my code until now:

insert into table1 ( num, val)
select (( select max(num) from table1) + row_number() over (order by num)), val
from table1

Here is the error I get:

Subquery returned more than 1 value. This is not permitted when the subquery follows =, !=, <, <= , >, >= or when the subquery is used as an expression.

UPDATE The error comes from the trigger so I posted a new question regarding the trigger: SQL Server 2012 trigger: Doesnt work with multiple rows inserted

Answer 1

You should be using window functions instead of a subquery:

insert into table1 (num, val)
    select ( max(num) over () + row_number() over (order by num) ), val
    from table1;

However, the query in your question cannot return that error, because an aggregation query with no group by always returns exactly one row.