In SQL Server, CHAR, VARCHAR, and NVARCHAR are data types used to store character strings. However, they have different characteristics, storage requirements, and use cases. Here’s a detailed comparison of these data types:

1. CHAR

• Definition:

  • CHAR is a fixed-length character data type.

• Storage:

  • It always uses the defined length in bytes, regardless of the actual length of the string stored. For example, if you define a CHAR(10) and store a string of 5 characters, it will still use 10 bytes of storage, padding the remaining 5 bytes with spaces.

• Use Case:

  • Best used when the length of the data is consistent. For example, storing fixed-length codes like country codes or status codes.

• Example:

  sql
  1CREATE TABLE ExampleTable (
  2    FixedLengthColumn CHAR(10)
  3);

2. VARCHAR

• Definition:

  • VARCHAR is a variable-length character data type.

• Storage:

  • It uses only the actual length of the string stored, plus 2 bytes for length information. For example, if you define a VARCHAR(10) and store a string of 5 characters, it will use 5 + 2 = 7 bytes of storage.

• Use Case:

  • Best used when the length of the data varies significantly. For example, storing names, addresses, or any text where the length can change.

• Example:

  sql
  1CREATE TABLE ExampleTable (
  2    VariableLengthColumn VARCHAR(10)
  3);

3. NVARCHAR

• Definition:

  • NVARCHAR is a variable-length Unicode character data type.

• Storage:

  • It uses 2 bytes per character, plus 2 bytes for length information. This allows it to store characters from multiple languages and special characters. For example, if you define an NVARCHAR(10) and store a string of 5 characters, it will use 5 * 2 + 2 = 12 bytes of storage.

• Use Case:

  • Best used when you need to store international characters or special symbols. For example, storing names in different languages or any text that requires Unicode support.

• Example:

  sql
  1CREATE TABLE ExampleTable (
  2    UnicodeColumn NVARCHAR(10)
  3);

Key Differences

Conclusion

• Use CHAR when you know the data will always be of a fixed length.
• Use VARCHAR when the length of the data can vary but does not require Unicode support.
• Use NVARCHAR when you need to store text in multiple languages or special characters that require Unicode.

Choosing the appropriate data type is crucial for optimizing storage and ensuring that your database can handle the character data you need.