Table: danish_consorts
Columns: birth
marriage
became_consort
ceased_to_be_consort
death
spouse

Question: Name the became consort for marriage of 4 april 1721
SQL: SELECT "became_consort" FROM danish_consorts WHERE "marriage" = '4 april 1721'

Question: Name the birth of the person that has a spouse of frederick iv and became consort of 4 april 1721
SQL: SELECT "birth" FROM danish_consorts WHERE "spouse" = 'frederick iv' AND "became_consort" = '4 april 1721'

Question: Name the became consort for ceased to be consort of 4 april 1588 husband's death
SQL: SELECT "became_consort" FROM danish_consorts WHERE "ceased_to_be_consort" = '4 april 1588 husband''s death'

Question: Name the marriage of the person who is married for christian viii
SQL: SELECT "marriage" FROM danish_consorts WHERE "spouse" = 'christian viii'