T-SQL String Constants (String Literals)

ETL+ target tables (tables and columns shown in the ETL Objects panel) only support string constants with single quotation marks, (not double quotation marks).

String constants, also known as string literals, may be used on the Design page, ETL SQL Statement panel and the option in the Replace Load type.

Examples

• 'X' AS [Type Code] ( ETL SQL Statement panel )

Microsoft Documentation

Character string constants are enclosed in single quotation marks and include alphanumeric characters (a-z, A-Z, and 0-9) and special characters, such as exclamation point (!), at sign (@), and number sign (#).
– https://learn.microsoft.com/en-us/sql/t-sql/data-types/constants-transact-sql?view=sql-server-ver16

• https://learn.microsoft.com/en-us/sql/t-sql/data-types/constants-transact-sql?view=sql-server-ver16

• https://learn.microsoft.com/en-us/sql/odbc/microsoft/string-limitations?view=sql-server-ver16