query T
select substring('pineapple' from 5 for 10 )
----
app

query T
select substring('pineapple' for 4 )
----
pine

query T
select substring('pineapple' from 5 )
----
apple

query T
select substring('pineapple' from 1 for null )
----

query T
select substring('pineapple' from null for 4 )
----

query T
select substring(null from 1 for 4 )
----