`*string vs. sql.NullString: When Should I Use Each for Handling NULLs in Go?`

Understanding the Difference between *string and sql.NullString

In the realm of programming, dealing with null values can be a complex task, especially when interfacing with databases. One such scenario arises when working with SQL null values in Go. To resolve this issue, developers often encounter the use of either *string or sql.NullString. However, understanding the distinction between these two data types is crucial.

sql.NullString: A Representation of SQL Null Values

sql.NullString is specifically designed to handle SQL null values. It's essentially a struct that encapsulates a string (String) and a boolean flag (Valid) indicating whether the string is valid or null. In the context of SQL, a null value is denoted by the special keyword "NULL."

Example Usage:

var username sql.NullString

// Assuming the database query retrieves a NULL value
err := db.QueryRow("SELECT username from users WHERE id = 1").Scan(&username)
if err == nil {
    if username.Valid {
        fmt.Println("Username:", username.String)
    } else {
        fmt.Println("Username is NULL")
    }
}

Null Checking with *string

In contrast, *string represents a pointer to a string. A nil pointer indicates that the underlying string value is null.

var username *string

// Again, assuming NULL is retrieved from the database
err := db.QueryRow("SELECT username from users WHERE id = 1").Scan(&username)
if err == nil {
    if username != nil {
        fmt.Println("Username:", *username)
    } else {
        fmt.Println("Username is NULL")
    }
}

The Distinction

The primary distinction between sql.NullString and *string lies in their handling of SQL null values. sql.NullString explicitly represents the "NULL" state, allowing for specific handling of null values. On the other hand, *string relies on the presence or absence of a nil pointer to determine nullity, which is commonly used in Go for representing optional values.

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