sql語句中當條件的數量非常大時where...in條件子句用什麼更好的方法代替?
When you need to pass a list of parameters into a MySQL, there are at least two method to do this:
- Issue a dynamical query which would fill an
IN
list with constant values - Fill a temporary table with these values then use it in a
JOIN
The second method is considered better for many reasons (you can easily reuse the values, it's more injection-proof etc.)
Leaving all these issues aside, let's compare these methods performance-wise.
We will create a table of 50,000 records, pass a list of 500 parameters (using both methods) and see which is faster:
We have created two stored procedures.
The first procedure, prc_temporary
, fills the temporary value using a dynamic query then issues the query using a JOIN
The second procedure, prc_range
, just uses the IN
list in a dynamic query, also in a
loop.
Let's run both procedures:
1.
CALL
prc_list(1000)
1.
CALL
prc_temporary(1000)
However, if we change the procedures and leave but 20
, both procedures have almost the same performance:
1.
CALL
prc_list(1000)
1.
CALL
prc_temporary(1000)
We see that for a large list of parameters, passing them in a temporary table is much faster that as a constant list, while for small lists performance is almost the same.
Using a temporary table is the best way to pass large arrays of parameters in MySQL.