How to pass an array into a SQL Server stored procedure

Question

How to pass an array into a SQL Server stored procedure?

For example, I have a list of employees. I want to use this list as a table and join it with another table.

Answer 1

Context is always important, such as the size and complexity of the array. For small to mid-size lists, several of the answers posted here are just fine, though some clarifications should be made:

• For splitting a delimited list, a SQLCLR-based splitter is the fastest. There are numerous examples around if you want to write your own, or you can just download the free SQL# library of CLR functions (which I wrote, but the String_Split function, and many others, are completely free).
• Splitting XML-based arrays can be fast, but you need to use attribute-based XML, not element-based XML (which is the only type shown in the answers here, though @AaronBertrand's XML example is the best as his code is using the text() XML function. For more info (i.e. performance analysis) on using XML to split lists, check out "Using XML to pass lists as parameters in SQL Server" by Phil Factor.
• Using TVPs is great (assuming you are using at least SQL Server 2008, or newer) as the data is streamed to the proc and shows up pre-parsed and strongly-typed as a table variable. HOWEVER, in most cases, storing all of the data in DataTable means duplicating the data in memory as it is copied from the original collection. Hence using the DataTable method of passing in TVPs does not work well for larger sets of data (i.e. does not scale well).
• XML, unlike simple delimited lists of Ints or Strings, can handle more than one-dimensional arrays, just like TVPs. But also just like the DataTable TVP method, XML does not scale well as it more than doubles the datasize in memory as it needs to additionally account for the overhead of the XML document.

With all of that said, IF the data you are using is large or is not very large yet but consistently growing, then the IEnumerable TVP method is the best choice as it streams the data to SQL Server (like the DataTable method), BUT doesn't require any duplication of the collection in memory (unlike any of the other methods). I posted an example of the SQL and C# code in this answer:

Pass Dictionary to Stored Procedure T-SQL