Ensuring Data Consistency: How to Insert Default Values in SQL Server

Solutions:

There are three main approaches to handle null parameters and insert default values in SQL Server:

Using Default Constraints:

• Define a default constraint on the table column that specifies the default value to be used when no value is explicitly inserted.
• Example:

CREATE TABLE MyTable (
  ID int PRIMARY KEY,
  Name nvarchar(50) NOT NULL,
  Age int DEFAULT 25
);

• In this example, the Age column has a default constraint set to 25. If you insert a record without specifying a value for Age, the default value of 25 will be used.

Using T-SQL Functions:

• Utilize T-SQL functions like COALESCE or ISNULL within your INSERT statement to conditionally insert the default value if the parameter is null.

DECLARE @Name nvarchar(50), @Age int;
SET @Name = 'foo';
SET @Age = NULL;

INSERT INTO MyTable (Name, Age)
VALUES (@Name, COALESCE(@Age, 25)); -- Use COALESCE

• Here, COALESCE checks if @Age is null. If it is, 25 is inserted instead. You can replace 25 with your desired default value.
• Alternatively, you can use ISNULL:

INSERT INTO MyTable (Name, Age)
VALUES (@Name, ISNULL(@Age, 25));

Using Conditional Logic in Stored Procedures:

• In stored procedures, you can use conditional statements like IF to check if the parameter is null and then assign the default value before inserting.

CREATE PROCEDURE InsertData (@Name nvarchar(50), @Age int)
AS
BEGIN
  DECLARE @DefaultAge int;
  SET @DefaultAge = 25;

  IF @Age IS NULL
    SET @Age = @DefaultAge;

  INSERT INTO MyTable (Name, Age)
  VALUES (@Name, @Age);
END;

Related Issues:

• Data Type Mismatch: Ensure the data type of the default value matches the column data type to avoid errors.
• Logic Errors: Double-check your conditional logic and function usage to prevent unexpected behavior with null values.

Choosing the Right Approach:

• Default Constraints: Ideal for simple scenarios where the default value is constant and applies to all inserts.
• T-SQL Functions: Offer flexibility within your INSERT statement, especially when dealing with different default values based on conditions.
• Stored Procedures: Useful for complex logic involving multiple parameters and conditional assignments.