CHAR vs. VARCHAR in SQL: When Should I Choose Fixed-Width Data Types?

Selecting CHAR over VARCHAR: When to Use Fixed-Width Types

While it's generally advisable to use VARCHAR for text fields, there are specific scenarios where CHAR offers advantages. According to the "When to Use CHAR over VARCHAR in SQL?" discussion, the decision hinges on data length characteristics:

Use CHAR when:

• All values have a fixed width (close to the same length)
• Data length variations are minimal (within two characters)

In such cases, CHAR provides the following benefits:

• Space efficiency: CHAR minimizes wasted storage space since all rows are of the same length.
• Potential performance improvement: Databases may process fixed-length data more quickly than variable-length data.

Example:
Assuming a one-byte character set:

• CHAR(6) for "FooBar" requires 6 bytes (no overhead)
• VARCHAR(100) for "FooBar" uses 8 bytes (2 bytes of overhead)

Use VARCHAR when:

• Length variations are significant
• Data lengths are unknown or may vary greatly

VARCHAR accommodates such variations while incurring minimal storage overhead (typically 1-2 bytes per row).

Note:

• Multi-byte character sets: VARCHAR becomes a more favorable choice, as CHAR overhead increases for multi-byte characters.
• Storage considerations: VARCHAR doesn't waste empty space, as it stores the actual content length. However, declaring a larger maximum size in VARCHAR limits storage accordingly.
• SQL Server anomaly: Microsoft Transact-SQL documentation seemingly contradicts the general recommendation, suggesting that CHAR is faster for variable-length data. However, this may be an error or unclear language in the documentation.

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