don't forget about transactions. Performance is good, but simple (IF EXISTS..) approach is very dangerous.
When multiple threads will try to perform Insert-or-update you can easily
get primary key violation.
Solutions provided by @Beau Crawford & @Esteban show general idea but error-prone.
To avoid deadlocks and PK violations you can use something like this:
begin tran
if exists (select * from table with (updlock,serializable) where key = @key)
begin
update table set ...
where key = @key
end
else
begin
insert into table (key, ...)
values (@key, ...)
end
commit tran
or
begin tran
update table with (serializable) set ...
where key = @key
if @@rowcount = 0
begin
insert into table (key, ...) values (@key,..)
end
commit tran
Assuming three columns in the table: ID, NAME, ROLE
BAD: This will insert or replace all columns with new values for ID=1:
INSERT OR REPLACE INTO Employee (id, name, role)
VALUES (1, 'John Foo', 'CEO');
BAD: This will insert or replace 2 of the columns... the NAME column will be set to NULL or the default value:
INSERT OR REPLACE INTO Employee (id, role)
VALUES (1, 'code monkey');
GOOD: Use SQLite On conflict clause
UPSERT support in SQLite! UPSERT syntax was added to SQLite with version 3.24.0!
UPSERT is a special syntax addition to INSERT that causes the INSERT to behave as an UPDATE or a no-op if the INSERT would violate a uniqueness constraint. UPSERT is not standard SQL. UPSERT in SQLite follows the syntax established by PostgreSQL.
GOOD but tedious: This will update 2 of the columns.
When ID=1 exists, the NAME will be unaffected.
When ID=1 does not exist, the name will be the default (NULL).
INSERT OR REPLACE INTO Employee (id, role, name)
VALUES ( 1,
'code monkey',
(SELECT name FROM Employee WHERE id = 1)
);
This will update 2 of the columns.
When ID=1 exists, the ROLE will be unaffected.
When ID=1 does not exist, the role will be set to 'Benchwarmer' instead of the default value.
INSERT OR REPLACE INTO Employee (id, name, role)
VALUES ( 1,
'Susan Bar',
COALESCE((SELECT role FROM Employee WHERE id = 1), 'Benchwarmer')
);
Best Answer
Have a look at http://sqlite.org/lang_conflict.html.
You want something like:
Note that any field not in the insert list will be set to NULL if the row already exists in the table. This is why there's a subselect for the
ID
column: In the replacement case the statement would set it to NULL and then a fresh ID would be allocated.This approach can also be used if you want to leave particular field values alone if the row in the replacement case but set the field to NULL in the insert case.
For example, assuming you want to leave
Seen
alone: