CREATE TABLE table_59731 ("Name  ( year commissioned ) " CLOB, "Owner/operator" CLOB, "Length" CLOB, "Maximum diameter" CLOB, "From/to" CLOB, "Licence number" CLOB)

What is the license number where the maximum diameter is 400 mm?
SELECT "Licence number" FROM table_59731 WHERE "Maximum diameter" = '400 mm'
SELECT "Licence number" FROM "table_59731" WHERE "Maximum diameter" = '400 mm'