ORACLE functions NVL, NVL2, Nullif

NULL refers to a null value, or an illegal value.

1, NVL (expr1, expr2) function

EXPR1 is null, returns EXPR2, is not NULL, returns EXPR1. Note that the two types should be consistent

Eg:select NVL (column,0) from DUAL--column value is null, it is displayed as 0

2, NVL2 (Expr1, EXPR2, EXPR3)

EXPR1 is not NULL, returns EXPR2, or null, returning EXPR3. EXPR3 will be converted to EXPR2 type if the EXPR2 and EXPR3 types are different

Eg:select NVL2 (column,1,0) The value of the from DUAL--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 return null, not equal to return EXPR1

ORACLE functions NVL, NVL2, Nullif