Table schema:
CREATE TABLE table_name_30 (games INTEGER, win_percentage VARCHAR, Pwin_percentage VARCHAR, — VARCHAR, term_ VARCHAR, c_ VARCHAR)

Question: What is the sum of the game with a PWin% of —, Term [c] of 1987–1988, and Win% less than 0.506?
SQL: SELECT SUM(games) FROM table_name_30 WHERE Pwin_percentage = — AND term_[c_] = "1987–1988" AND win_percentage < 0.506