How to execute a Table valued function

Understanding TVFs - The fundamentals

Table-valued Functions (TVFs) in SQL Server return a table that we can use in the FROM clause of a SELECT statement as easy as pie. Here are the basics:

• Naming the Function: Be sure to include the function's schema, typically dbo, but not for inline TVFs with a default schema.
• Parameters Passing: Serve the required parameters straight within the parentheses after the function.
• Selecting the Data: The good old SELECT * FROM ... syntax will get you the data, just consider the TVF as a regular table.

This is just like picking a cable channel - you opt for the right function and give parameters to get the data you want.

Parameters and Result sets

Consider a TVF, dbo.SplitString, which expects a VARCHAR parameter. It takes this string, splits it around commas, and dishes out a table with each item as a separate row. To call this function, you'd do:

SELECT * FROM dbo.SplitString('apple,banana,carrot'); -- Who knew SQL was (fruit) salad bar?
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Here, you'd get a table with a lone column, typically named as per the function's expected return, with each fruit item as a separate row.

For TVFs wanting more parameters, feed them in as follows:

SELECT * FROM dbo.YourFunction(param1, param2, param3);
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Hurdles along the way

While working with table-valued functions, ensure to:

• Pass all the necessary parameters - anything less will only warrant errors.
• Not mix 'em up with scalar-valued functions, which return a single result and are used differently.
• Understand the cross apply and outer apply operators. They allow you to connect a TVF with another table, adding more flexibility than usual JOIN operations.

Advanced use cases

Beyond simple SELECT queries, here are advanced situations:

• Merging with Tables: Join TVFs with other tables to get complicated queries:

SELECT t.*, f.columnName
FROM someTable AS t
JOIN dbo.YourFunction(@Param) AS f
ON t.someColumn = f.matchingColumn; -- SQL Server Marriages: When tables mate...
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• Considering Performance: For enormous datasets, TVFs could be slowpokes. Check indexes on tables or rewrite the TVF logic for efficiency.
• Application of 'Apply' Operators: CROSS APPLY or OUTER APPLY can integrate TVFs "row by row", like a meticulous artist. This is golden when the function needs to iterate over each row returned by another query.

SELECT t.*, f.*
FROM someTable AS t
CROSS APPLY dbo.YourFunction(t.columnName) AS f; -- The secret handshake between tables and functions.
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