Below is the list of tables from the database along with their columns and datatype. Need to generate an accurate SQL query for the question.
Only use the columns present in the respective table. Only use the columns which are required to generate the SQL query. Only use table joins if required and not otherwise.

### Tables ###
TABLE: CREATE TABLE table_name_15 ( high_rebounds VARCHAR, location_attendance VARCHAR, date VARCHAR )

### Question ###
What is High Rebounds, when Location Attendance is 'Madison Square Garden Unknown', and when Date is 'May 18'?

### Accurate SQL ###

SELECT high_rebounds FROM table_name_15 WHERE location_attendance = "madison square garden unknown" AND date = "may 18"