Swap unique indexed column values in database

Question

I have a database table and one of the fields (not the primary key) is having a unique index on it. Now I want to swap values under this column for two rows. How could this

Answer 1

There is another approach that works with SQL Server: use a temp table join to it in your UPDATE statement.

The problem is caused by having two rows with the same value at the same time, but if you update both rows at once (to their new, unique values), there is no constraint violation.

Pseudo-code:

-- setup initial data values:
insert into data_table(id, name) values(1, 'A')
insert into data_table(id, name) values(2, 'B')

-- create temp table that matches live table
select top 0 * into #tmp_data_table from data_table

-- insert records to be swapped
insert into #tmp_data_table(id, name) values(1, 'B')
insert into #tmp_data_table(id, name) values(2, 'A')

-- update both rows at once! No index violations!
update data_table set name = #tmp_data_table.name
from data_table join #tmp_data_table on (data_table.id = #tmp_data_table.id)

Thanks to Rich H for this technique. - Mark