How many players are there for mens singles when chen qi ma lin played mens doubles?
CREATE TABLE table_28138035_20 (
    mens_singles VARCHAR,
    mens_doubles VARCHAR
)
SELECT COUNT(mens_singles) FROM table_28138035_20 WHERE mens_doubles = "Chen Qi Ma Lin"
Below are sql tables schemas paired with instruction that describes a task. Using valid SQLite, write a response that appropriately completes the request for the provided tables. ### Instruction: How many players are there for mens singles when chen qi ma lin played mens doubles? ### Input: CREATE TABLE table_28138035_20 (
    mens_singles VARCHAR,
    mens_doubles VARCHAR
) ### Response: SELECT COUNT(mens_singles) FROM table_28138035_20 WHERE mens_doubles = "Chen Qi Ma Lin"