CREATE TABLE table_8870 ("Name" CLOB, "Nationality" CLOB, "Position" CLOB, "Crewe Alexandra career" CLOB, "Appearances" FLOAT, "Goals" FLOAT)

What is the position when the Crewe Alexandra career is 1988 1990, with 31 goals?
SELECT "Position" FROM table_8870 WHERE "Crewe Alexandra career" = '1988–1990' AND "Goals" = '31'
SELECT "Position" FROM "table_8870" WHERE "Crewe Alexandra career" = '1988–1990' AND "Goals" = '31'