How to determine NULL in SQL Server, Oracle, and MySQL

This article describes how to replace NULL values in SQL Server, Oracle, and MySQL.
In SQL Server Oracle MySQL What should I do if I find a NULL value in the database?
1. MSSQL: ISNULL ()
Syntax
Java code
Copy codeThe Code is as follows:
ISNULL (check_expression, replacement_value)
ISNULL (check_expression, replacement_value)

Parameters
Check_expression
Whether the expression is NULL is checked. Check_expression can be of any type.
Replacement_value
The expression returned when check_expression is NULL. Replacement_value must be of the same type as check_expresssion.
Return type
Returns the same type as check_expression.
Note
If check_expression is not NULL, the value of this expression is returned; otherwise, the value of replacement_value is returned.
2. Oracle: NVL ()
Syntax
Java code
Copy codeThe Code is as follows:
NVL (eExpression1, eExpression2)
NVL (eExpression1, eExpression2)

Parameters
EExpression1, eExpression2
If the calculation result of eExpression1 is null, NVL () returns eExpression2. If the calculation result of eExpression1 is not null, eExpression1 is returned. EExpression1 and eExpression2 can be any data type. If both eExpression1 and eExpression2 are null values, NVL () returns NULL.
Return Value Type
Numeric, currency, logical, or null
Description
If null or null values are not supported, you can use NVL () to remove null values in the calculation or operation.
3. Mysql: IFNULL ()
Syntax
Java code
Copy codeThe Code is as follows:
IFNULL (expr1, expr2)
IFNULL (expr1, expr2)

Parameters
Expr1, expr2
If expr1 is not NULL, IFNULL () returns expr1; otherwise, expr2 is returned. IFNULL () returns a number or string value, depending on the context in which it is used