SSIS expressions: introduction and examples

Introduction to SSIS Expressions:

Expressions play a crucial role in SSIS (SQL Server Integration Services) by providing a dynamic and flexible way to configure and control various aspects of your data integration workflows. Here are several key points highlighting the importance of expressions in SSIS:

Use Cases and Importance:

  • Expressions allow you to dynamically configure properties of SSIS tasks, connections, variables, and other components
  • Since expressions are evaluated at runtime, you can adapt your SSIS packages to handle different scenarios based on the conditions and data available during execution
  • Support conditional logic, allowing you to build complex workflows with branching and decision-making based on runtime conditions.
  • Can be used to implement dynamic error handling. For example, you can set the value of a variable based on the success or failure of a particular task and then use that variable in subsequent control flow decisions
  • You can design SSIS packages that are more reusable and easier to maintain
  • Expressions are commonly used to parameterize connection strings. This allows you to change connection details, such as server names or database names, dynamically, making your packages more versatile and adaptable to different environments.

Expression Syntax

You can use a variety of operators, functions, and constants to build dynamic and flexible expressions. Here are some common operators, functions, and constants available for use:

Operators:

Arithmetic Operators:

  • + (Addition)
  • - (Subtraction)
  • * (Multiplication)
  • / (Division)
  • % (Modulus)

Comparison Operators:

  • == or = (Equal to)
  • != or <> (Not equal to)
  • < (Less than)
  • > (Greater than)
  • <= (Less than or equal to)
  • >= (Greater than or equal to)

Logical Operators:

  • && or AND (Logical AND)
  • || or OR (Logical OR)
  • ! or NOT (Logical NOT)

Concatenation Operator:

  • + (Concatenates two strings)

Functions:

String Functions:

  • LEN(string) - Returns the length of the string.
  • SUBSTRING(string, start, length) - Returns a portion of the string.
  • LEFT(string, length) - Returns the leftmost characters of a string.
  • RIGHT(string, length) - Returns the rightmost characters of a string.
  • LTRIM(string) and RTRIM(string) - Removes leading or trailing spaces.

Mathematical Functions:

  • ABS(number) - Returns the absolute value of a number.
  • ROUND(number, decimals) - Rounds a number to a specified number of decimal places.
  • CEILING(number) - Returns the smallest integer greater than or equal to a number.
  • FLOOR(number) - Returns the largest integer less than or equal to a number.

Date and Time Functions:

  • GETDATE() - Returns the current date and time.
  • DATEPART(part, date) - Returns a specific date part (e.g., year, month, day).
  • DATEDIFF(interval, startdate, enddate) - Returns the difference between two dates.

Conversion Functions:

  • CONVERT(data_type, expression, style) - Converts an expression from one data type to another.

NULL Functions:

  • ISNULL(expression, replacement_value) - Returns replacement_value if the expression is NULL; otherwise, returns the expression.

Constants:

Numeric Constants:

  • 1, 2.5, -10, etc.

String Constants:

  • 'Hello', '123', etc.

Boolean Constants:

  • TRUE or FALSE

Null Constant:

  • NULL

Compatibility Considerations

SSIS may implicitly convert data types into expressions. For example, when performing operations between different numeric data types, SSIS may automatically convert them to the most compatible type.

You can use explicit type conversion functions (e.g., (DT_STR) , (DT_WSTR) , (DT_DATE) ) to convert data types explicitly. This is useful when you want to ensure a specific data type for an expression result.

Ensure that the data types of operands in expressions are compatible to avoid data type mismatch errors. For example, adding a string and a numeric value without proper conversion may result in an error.

How to use the Expression Builder in SSIS.

Open the SSIS project containing the package you want to work on or create a new SSIS project and package.

In the SSIS package, identify the property you want to set an expression. This could be a property of a task, connection manager, variable, or another SSIS object.

For Connection manager or task from the control flow, you need to right-click in It and select ‘properties’

For a component inside a data flow, you need to right-click inside the data flow:

Properties from Data flow

In the Properties window, find the property for which you want to set an expression. Then select the ellipsis (…) button next to the Expressions value. This action will open the Expression Builder dialog. Here is an example of a REST API task:

Expression from REST API task

In the Expression editor, you’ll find a list of functions, operators, and variables on the left side, select the function you need and add it to the expression. Select the ellipsis (…) located on the right side of the property value and use the variable(s) you want to use like the following example:

Expression example with variable

Once you’ve built your expression, click “OK” to close the Expression Builder. Save your SSIS package to apply the changes.

Here is an example where you can use it in a variable: convert Date type to string in the format “dd-mm-yyyy”. Select the ellipsis (…) and use the following example in the expression:

RIGHT("0" + (DT_STR, 2, 1252) DATEPART("dd" , GETDATE()), 2) + "-" + RIGHT("0" + (DT_STR, 2, 1252) DATEPART("mm" , GETDATE()), 2) + "-" +  (DT_STR, 4, 1252) DATEPART("yy" , GETDATE())