Go's *string vs. sql.NullString: When to Use Which for Handling NULL Strings?

Distinguishing between *string and sql.NullString in Go

Understanding the distinction between *string and sql.NullString can be crucial when working with SQL NULL values in Go. While both options allow for representing null strings, they differ in their implementation.

sql.NullString: Representing SQL NULL

The sql.NullString type from the database/sql package specifically caters to SQL NULL values. As SQL has a distinct concept of null values, the sql.NullString struct is designed to represent this concept in Go. It consists of two fields: String and Valid. The String field holds the string value, while the Valid field indicates whether the String field is valid.

Example:

var nullValue sql.NullString

nil *string: Pointer to a Nonexistent String

In contrast, a nil *string represents a pointer to a non-existent string. When the pointer is nil, it signifies the absence of a string value.

Example:

var pointerValue *string
*pointerValue = "Hello"
pointerValue = nil // sets the pointer to nil, effectively deleting the string

Differences in Usage

The main difference between the two options lies in their usage. sql.NullString is used to represent SQL NULL values, ensuring compatibility with the database. On the other hand, a nil *string is typically used when handling Go-specific null values.

Additionally, it's important to note that checking for nil values with sql.NullString and string is different. For sql.NullString, one checks the Valid field to determine if the String field is valid. For string, one simply checks if the pointer is nil.

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