Oracle null value handling function
/ * usage of NUL, NVL2 and NULLIF in Oracle * /
NULL refers to a null value or an illegal value.
1. NVL (expr1, expr2) function
Expr1 is NULL, expr2; is not NULL, expr1 is returned. Note that the two types should be the same.
Eg:SELECT NVL (column,0) FROM DUAL-- if the value of column is null, it is displayed as 0
2. NVL2 (expr1, expr2, expr3)
Expr1 is not NULL, expr2; is NULL, expr3 is returned. If the expr2 and expr3 types are different, expr3 will be converted to the expr2 type
Eg:SELECT NVL2 (column,1,0) FROM DUAL-if the value of column is not null, it is displayed as 1, and if the value of the column name is null, it is displayed as 0
3. NULLIF (expr1, expr2)-> expr1 and expr2 are equal to return NULL, and if not equal, return expr1
