The sp_executesql stored procedure is a powerful tool in SQL Server that allows you to execute dynamic SQL queries. Dynamic SQL queries are queries that are constructed at runtime, usually based on user input or other dynamic factors. This flexibility can be very useful in scenarios where the structure or conditions of a query need to change dynamically.

Let’s start by understanding what dynamic SQL is. In many cases, you may have a query in the form of a string. For example, if you have a search functionality on a website where users can search for products by name, the product name entered by the user will be concatenated with a SELECT query to form another string. This string needs to be executed dynamically because different users will search for different product names, resulting in different queries.

The sp_executesql stored procedure comes in handy in such scenarios. It allows you to execute dynamic SQL queries by simply passing the query string to the procedure. Let’s take a look at an example:

DECLARE @SQL_QUERY NVARCHAR(128)
SET @SQL_QUERY = N'SELECT id, name, price FROM Books WHERE price > 4000'
EXECUTE sp_executesql @SQL_QUERY

In the above example, we declare a variable @SQL_QUERY and initialize it with a string query. We then execute the sp_executesql stored procedure by passing the query string to it. The result is a dynamic execution of the query, returning the id, name, and price of books where the price is greater than 4,000.

Another useful feature of the sp_executesql stored procedure is the ability to pass parameters. This is particularly handy when you don’t know the values used to filter records before runtime. Here’s an example:

DECLARE @CONDITION NVARCHAR(128)
DECLARE @SQL_QUERY NVARCHAR(MAX)
DECLARE @PARAMS NVARCHAR(1000)

SET @CONDITION = 'WHERE price > @LowerPrice AND price < @HigherPrice'
SET @SQL_QUERY = N'SELECT id, name, price FROM Books ' + @CONDITION
SET @PARAMS = '@LowerPrice INT, @HigherPrice INT'

EXECUTE sp_executesql @SQL_QUERY, @PARAMS, @LowerPrice = 3000, @HigherPrice = 6000

In this example, we declare three variables: @CONDITION, @SQL_QUERY, and @PARAMS. The @CONDITION variable contains a WHERE clause with two parameters: @LowerPrice and @HigherPrice. We then concatenate the @CONDITION variable with the @SQL_QUERY variable to form the final query string. The @PARAMS variable stores the list of parameters used in the query.

When executing the sp_executesql stored procedure, we pass the query string, the parameter list, and the actual parameter values. In the output, we will see the records where the price is between 3,000 and 6,000.

In conclusion, the sp_executesql stored procedure is a powerful tool in SQL Server that allows you to execute dynamic SQL queries. It provides flexibility and convenience when dealing with queries that need to be constructed at runtime. Whether you need to execute a simple dynamic query or pass parameters to filter records, the sp_executesql stored procedure has got you covered.