What is the difference between CHAR and VARCHAR?

CHAR and VARCHAR are both data types used to store text in databases, but they handle storage differently. CHAR is a fixed-length type, meaning it always reserves space for the maximum defined length, even if the stored data is shorter. For example, a CHAR(10) column will use 10 characters of storage regardless of whether you store “yes” (3 characters) or “hello” (5 characters). The remaining space is padded with blank characters. In contrast, VARCHAR is variable-length, allocating only the space needed for the actual data plus a small overhead (usually 1-2 bytes) to track the length. A VARCHAR(10) column storing “yes” uses approximately 4 bytes (3 characters + 1 byte for length), making it more space-efficient for shorter or variable-length data.

The choice between CHAR and VARCHAR depends on the nature of the data. CHAR is ideal for fields where values are consistently the same length, such as codes (e.g., country codes like “US” or “CA” stored as CHAR(2)) or fixed-format identifiers (e.g., a 6-character product SKU). Using CHAR in these cases avoids the overhead of storing length information and can improve read/write speed for fixed-length records. VARCHAR is better suited for data with unpredictable lengths, like names, addresses, or descriptions. For example, storing a user’s email address in VARCHAR(255) ensures space isn’t wasted if the address varies from 15 to 50 characters. However, VARCHAR’s variable nature introduces minor overhead when calculating storage positions, which can slightly impact performance in very high-throughput systems.

When deciding between the two, consider storage efficiency and performance trade-offs. CHAR wastes space for shorter values but offers faster access due to predictable offsets in fixed-length records. VARCHAR saves space but may require slightly more processing to manage variable lengths. For instance, a CHAR(200) column holding an average of 10 characters per entry would waste 190 characters per row, whereas VARCHAR(200) would use only the necessary space. Additionally, some databases handle trailing spaces differently: CHAR pads values with spaces, which are typically trimmed on retrieval, while VARCHAR stores the exact input. If your data varies widely in length or you prioritize storage optimization, VARCHAR is usually the better choice. For strictly uniform data, CHAR can simplify storage management and improve performance.