When to Use Special SQL Data Types

When should BIT, XML, JSON, ROWVERSION, and SQL_VARIANT be used?

These types serve specialized purposes and should be used only when they match the data requirement.

1. BIT

Stores Boolean-like values:

• 0 — False

• 1 — True

• NULL — Unknown, if the column is nullable

IsActive BIT NOT NULL DEFAULT 1

Use it for yes/no conditions:

IsPublished BIT
IsDeleted   BIT
HasAccess   BIT

SQL Server converts any non-zero numeric value assigned to BIT into 1.

2. XML

Stores valid XML documents or fragments.

CREATE TABLE Orders
(
    OrderId INT,
    OrderDetails XML
);

INSERT INTO Orders
VALUES
(
    1,
    '<order><product>Laptop</product><quantity>2</quantity></order>'
);

Use XML when:

• Data naturally follows an XML structure

• Integrating with XML-based systems

• XML validation and querying are required

• Using SQL Server XML methods such as value(), query() and nodes()

Avoid it for ordinary relational data that can be stored in properly designed columns and tables.

3. JSON

JSON is useful for flexible or semi-structured data, such as:

• API request and response payloads

• Dynamic product attributes

• Application settings

• Data whose properties vary between records

CREATE TABLE Products
(
    ProductId  INT,
    Attributes NVARCHAR(MAX)
        CHECK (ISJSON(Attributes) = 1)
);

INSERT INTO Products
VALUES
(
    1,
    N'{"color":"Black","memory":"16GB"}'
);

Query JSON properties:

SELECT JSON_VALUE(Attributes, '$.color')
FROM Products;

Traditionally, SQL Server stores JSON in NVARCHAR; SQL Server 2025 introduces a native JSON type, with availability depending on the SQL Server platform and version. SQL Server provides functions such as ISJSON, JSON_VALUE, JSON_QUERY, JSON_MODIFY and OPENJSON. Microsoft JSON documentation

Avoid JSON when the properties are stable and need frequent joins, constraints, indexing or relational reporting. Normal columns are usually better in that situation.

4. ROWVERSION

ROWVERSION is an automatically generated 8-byte binary value that changes whenever a row is inserted or updated.

CREATE TABLE Products
(
    ProductId INT PRIMARY KEY,
    Price     DECIMAL(10,2),
    Version   ROWVERSION
);

It is mainly used for optimistic concurrency control:

UPDATE Products
SET Price = 1500
WHERE ProductId = 1
  AND Version = @OriginalVersion;

If zero rows are updated, another user may have modified the record after it was originally read.

Important:

• It does not store a date or time.

• It is generated automatically.

• A table can contain only one ROWVERSION column.

• Do not use it as a primary key.

• The older synonym TIMESTAMP is deprecated; use ROWVERSION.

Microsoft ROWVERSION documentation

5. SQL_VARIANT

SQL_VARIANT allows one column to store values of different supported scalar types.

CREATE TABLE Settings
(
    SettingName  VARCHAR(50),
    SettingValue SQL_VARIANT
);

INSERT INTO Settings VALUES ('MaxAttempts', 5);
INSERT INTO Settings VALUES ('TaxRate', CAST(18.50 AS DECIMAL(5,2)));
INSERT INTO Settings VALUES ('StartDate', CAST('2026-09-17' AS DATE));

Use it only for specialized situations such as:

• Generic configuration tables

• Metadata or property-value systems

• Values whose types genuinely vary

Disadvantages:

• More complex querying and conversion

• Harder validation

• Limited application/driver support

• Not all SQL Server data types can be stored

• Usually weaker database design than strongly typed columns

Inspect its stored base type using:

SELECT SQL_VARIANT_PROPERTY(SettingValue, 'BaseType')
FROM Settings;

Key interview points

• BIT stores Boolean flags.

• XML stores and queries XML structures.

• JSON is used for semi-structured data; historically it is stored in NVARCHAR.

• ROWVERSION detects whether a row has changed; it is not a timestamp.

• SQL_VARIANT stores different scalar types but should be used sparingly.

• Do not use XML or JSON as a replacement for proper relational modelling.

• Choose normal, strongly typed columns whenever the data structure is predictable.