Below is an context that describes a sql query, paired with an question that provides further information. Write an answer that appropriately completes the request.  # noqa: E501
### Context:
CREATE TABLE CMI_cross_references (source_system_code VARCHAR)
### Question:
How many different source system code for the cmi cross references are there?
### Answer:
SELECT COUNT(DISTINCT source_system_code) FROM CMI_cross_references