PL/SQL function learning-nvl (ARG, value)

Obtain the total value of a field through the query. If this value is null, a default value is provided.
Select nvl (sum (T. dwxhl), 1) from tb_jhde t where zydm =-1Nvl (ARG, value) indicates that if the previous Arg value is null, the returned value is the following value.

Another useful method
Declare I intener
Select nvl (sum (T. dwxhl), 1) into I from tb_jhde t where zydm =-1In this way, the obtained total value is stored in variable I. If the queried value is null, the value is set to the default value of 1.