CREATE TABLE table_name_6 (opening_date VARCHAR2, classification VARCHAR2, theatre VARCHAR2)

What is the opening date of the musical at the adelphi theatre?
SELECT opening_date FROM table_name_6 WHERE classification = "musical" AND theatre = "adelphi theatre"
SELECT "opening_date" FROM "table_name_6" WHERE "adelphi theatre" = "theatre" AND "classification" = "musical"