COALESCE takes any number of arguments and returns the first value that
is not null.
COALESCE(x,y,z) = x if x is not NULL
COALESCE(x,y,z) = y if x is NULL and y is not NULL
COALESCE(a,y,z) = z if x and y are NULL but z is not NULL
COALESCE(x,y,z) = NULL if x and y and z are all NULL
COALESCE can be useful when you want to replace a NULL value with
some other value. In this example you show the name of the party
for each MSP that has a party. For the MSP with no party (such as
Canavan, Dennis) you show the string None.
