SUBSTRING (SSIS Expression)
Applies to: 
SQL Server
SSIS Integration Runtime in Azure Data Factory
Returns the part of a character expression that starts at the specified position and has the specified length. The position parameter and the length parameter must evaluate to integers.
Syntax
SUBSTRING(character_expression, position, length)
Arguments
character_expression
Is a character expression from which to extract characters.
position
Is an integer that specifies where the substring begins.
length
Is an integer that specifies the length of the substring as number of characters.
Result Types
DT_WSTR
Remarks
SUBSTRING uses a one-based index. If position is 1, the substring begins with the first character in character_expression.
SUBSTRING works only with the DT_WSTR data type. A character_expression argument that is a string literal or a data column with the DT_STR data type is implicitly cast to the DT_WSTR data type before SUBSTRING performs its operation. Other data types must be explicitly cast to the DT_WSTR data type. For more information, see Integration Services Data Types and Cast (SSIS Expression).
SUBSTRING returns a null result if the argument is null.
All arguments in the expression can use variables and columns.
The length argument can exceed the length of the string. In that case, the function returns the remainder of the string.
Expression Examples
This example returns two characters, beginning with character 4, from a string literal. The return result is "ph".
SUBSTRING("elephant",4,2)
This example returns the remainder of a string literal, beginning at the fourth character. The return result is "phant". It is not an error for the length argument to exceed the length of the string.
SUBSTRING ("elephant",4,50)
This example returns the first letter from the MiddleName column.
SUBSTRING(MiddleName,1,1)
This example uses variables in the position and length arguments. If Start is 1 and Length is 5, the function returns the first five characters in the Name column.
SUBSTRING(Name,@Start,@Length)
This example returns the last four characters from the PostalCode variable beginning at the sixth character.
SUBSTRING (@PostalCode,6,4)
This example returns a zero-length string from a string literal.
SUBSTRING ("Redmond",4,0)