STRING_SPLIT skyrockets execution time of sql query - sql

Question

For a SQL query I need to split an input string into its integer components and select values from a table according to the provided integers.
My problem: if there are a lot of integers (>300), the query gets slower and slower, i.e. for around 600 integers it uses more than one minute!
Here a small example of the executed query:
DECLARE #inputStr VARCHAR(MAX) = '234,2344,12,523,5667,9825,345'
SELECT
surname,
firstname
FROM Addresses
WHERE id IN (SELECT CAST(value AS INTEGER) FROM STRING_SPLIT(#inputStr, ',')))
Is there a known problem to this or any improvements I could do?
I'm glad for any help!

Answer 1

The probleme is that any explicit values in a "IN" operator is translate by a multiple OR in the WHERE clause by the algebrizer, before optimizing the query...
A great number of values in the IN operator will allways causes a lack of performances, whatever the manner to do it... !
By creating a temporay table, you will have another query execution plan that will boost your performances.
Si try this way :
SELECT DISTINCT CAST(value AS INTEGER)
INTO #T
FROM STRING_SPLIT(#inputStr, ',');
SELECT surname,
firstname
FROM Addresses
WHERE id IN (SELECT value
FROM #T);
Eventually you can add a UNIQUE index to the temp table to increase performances :
SELECT DISTINCT CAST("value" AS INTEGER)
INTO #T
FROM STRING_SPLIT(#inputStr, ',');
CREATE UNIQUE INDEX X123456789 ON #T ("value");
SELECT surname,
firstname
FROM Addresses
WHERE id IN (SELECT value
FROM #T);

Answer 2

Personally, I would move STRING_SPLIT to a JOIN, as it could well be that SQL Server is running STRING_SPLIT once for every row:
SELECT surname,
firstname
FROM dbo.Addresses A
JOIN STRING_SPLIT(#InputStr,',') SS ON A.id = SS.[value];
If that is still slow, I would suggest you are missing an index on id. Considering it is the id, then you'll likely want it to be clustered, and probably the primary key:
ALTER TABLE dbo.Addresses ADD CONSTRAINT PK_Addresses PRIMARY KEY (id) CLUSTERED;

Answer 3

Could you try this?
DECLARE #inputStr VARCHAR(MAX) = '234,2344,12,523,5667,9825,345'
DROP TABLE IF EXISTS #TEST;
CREATE TABLE #TEST
(
[value] INT
);
INSERT INTO #TEST ([value])
SELECT value
FROM STRING_SPLIT(#inputStr, ',')
SELECT
surname,
firstname
FROM Addresses A
INNER JOIN #TEST B
ON A.id = b.value