Expression Language Patterns - SQL Server Integration Services Design Patterns - page 285

• Double-equal (==) comparison operators
• Simplified conditional ( if / then / else ) operators
Similarly, anyone experienced in T-SQL will find a great deal of familiar behavior
within the SSIS expression language:
• Case-insensitive function names
• Date arithmetic and string manipulation functions much like those in T-
SQL
The SSIS expression language is quite powerful, with its wide variety of functions
and operators. With native behavior including equality tests, type casts, string manipu-
lation, and date arithmetic, the use of expressions within SSIS packages can help to
overcome ETL challenges both large and small.
Limitations
As useful as the expression language is, there are a few key limitations to its use. Bear
in mind that these are relatively minor hang-ups; the SSIS expression language is not
intended to be a full-featured programming language, but rather a lightweight tool to
supplement the behavior of existing SSIS tasks and components. Among some of the
challenges are the following:
Expressions are limited to single-value statements : This almost
goes without saying since it's an expression language and not a pro-
gramming language. Still, it's worth mentioning that you can't, for
example, use a single expression to iterate through a list or process a
string character-by-character.
No IntelliSense : Unlike other scripting/expression environments,
there is no built-in IntelliSense within the native expression editors.
Although the expression editor in SSIS does have field, variable, and
function lists, the convenience and coding reliability of IntelliSense
has not yet made it into the product.
No error handling: This limitation is most visible when you attempt
to change data type or length. Because there is no try/catch or
TryParse() behavior found in the .NET-based languages, you can-