Replacing identified values in SQLServer, Oracle, and MySQL with a NULL_MySQL-mysql tutorial

Replace SQLServer, Oracle, and MySQL to find that the value is NULL. in SQL Server Oracle MySQL, when the database finds that a value is NULL, what should I do?

1. MSSQL: ISNULL ()

Syntax

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

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

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