So the question came up earlier today about the RIGHT() and LEFT() functions in the SSIS expression language.  Like the Transact-SQL functions, one might assume that these functions would exist in SSIS expression language to snatch a specified subset of a string.  That assumption would be only half right.

Don’t go digging for a LEFT() function in the expression language, because it ain’t there.  The RIGHT() function does indeed retrieve a specified number of characters, but strangely enough, there’s no corresponding LEFT() function:

Even though this is a pain for those just learning the expression language syntax, there are a couple of easy workarounds: One could simply use the SUBSTRING() function, with the second parameter – the starting point in the string – set to 1, which yields the same result.  If you want to get really crafty, you could use the RIGHT() combined with the REVERSE() function to simulate the behavior expected.

There’s already a Microsoft Connect item for this issue, and it’s planned to be fixed in a future version.