SQL Server pivot vs. multiple join
The answer will of course be "it depends" but based on testing this end...
Assuming
- 1 million products
product
has a clustered index onproduct_id
- Most (if not all) products have corresponding information in the
product_code
table - Ideal indexes present on
product_code
for both queries.
The PIVOT
version ideally needs an index product_code(product_id, type) INCLUDE (code)
whereas the JOIN
version ideally needs an index product_code(type,product_id) INCLUDE (code)
If these are in place giving the plans below
then the JOIN
version is more efficient.
In the case that type 1
and type 2
are the only types
in the table then the PIVOT
version slightly has the edge in terms of number of reads as it doesn't have to seek into product_code
twice but that is more than outweighed by the additional overhead of the stream aggregate operator
PIVOT
Table 'product_code'. Scan count 1, logical reads 10467Table 'product'. Scan count 1, logical reads 4750 CPU time = 3297 ms, elapsed time = 3260 ms.
JOIN
Table 'product_code'. Scan count 2, logical reads 10471Table 'product'. Scan count 1, logical reads 4750 CPU time = 1906 ms, elapsed time = 1866 ms.
If there are additional type
records other than 1
and 2
the JOIN
version will increase its advantage as it just does merge joins on the relevant sections of the type,product_id
index whereas the PIVOT
plan uses product_id, type
and so would have to scan over the additional type
rows that are intermingled with the 1
and 2
rows.
I don't think anyone can tell you which will be more efficient without knowledge of your indexing and table size.
That said, rather than hypothesizing about which is more efficient you should analyze the execution plan of these two queries.