CREATE TABLE table_50893 ("Race Title" CLOB, "Circuit" CLOB, "City / State" CLOB, "Date" CLOB, "Winner" CLOB, "Team" CLOB)

On what date did Dick Johnson with at Calder?
SELECT "Date" FROM table_50893 WHERE "Winner" = 'dick johnson' AND "Race Title" = 'calder'
SELECT "Date" FROM "table_50893" WHERE "Race Title" = 'calder' AND "Winner" = 'dick johnson'