Sql Server - In clause with a declared variable

sql

sql-injection

dynamic-sql

join-operations

byAlex Kataev·Dec 30, 2024

To use a variable like a list in an IN clause, tap into the power of table-valued parameters. Follow these steps: define a table type, initialize a table variable and stuff it with your values. You then nest this variable inside a subquery in your IN clause.

-- Create a table type
-- It's like you're the architect for this table city
CREATE TYPE TempIdList AS TABLE (Id INT); 

-- Initialize a table variable
DECLARE @IdFilter TempIdList;

-- Populate table variable
-- Think of those values that are going in as fresh fruits 
INSERT INTO @IdFilter VALUES (1), (2), (3); 

-- Use table variable in query
SELECT * FROM YourTable WHERE YourColumn IN (SELECT Id FROM @IdFilter);

Voila! Whatever the size of your list, flexible filtering within SQL Server is ensured.

When static SQL won't do

Dynamic SQL

Do you find your list vary often? Dynamic SQL is a lifesaver in this case. Craft your query with your variable's values included directly in the string. Watch those inputs though! Always sanitize to sidestep SQL injection.

DataTypes and NULLs

Ever seen bad reactions in chemistry labs? That's similar to what happens when there's a data type mismatch in your SQL. Also, keep an eye on NULL or empty values in your variables before executing dynamic SQL. You don't want surprises!

Handling CSVs and DataTypes

Data in SQL is a little fussier than your elementary school English exercises. Use T-SQL or CLR functions to convert comma-separated values into a filterable table. Got a VARCHAR? No problem! Convert it on the fly.

Watch those special characters!

Are special characters playfully messing around your list input? Cage them in! Always escape special characters while inserting them into a table variable to not upset your data.

A string of efficiencies

Joins

When it comes to handling complex filtering, JOIN operations are your go-to ally. Use a LEFT OUTER JOIN or an INNER JOIN to match your list to your table. That's some good team play!

VARCHAR(MAX) for big lists

Feeling heroic handling long lists? A VARCHAR(MAX) variable has your back, ensuring you don't bump into the VARCHAR field limit.

Efficiency in the air

Construct dynamic SQL carefully for stellar performance. A good rule of thumb? Limit your dynamic behaviour to the necessary, keeping your code more secure and manageable.

explain-codes / Sql / Sql Server - In clause with a declared variable

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