Q.Can you think of an attribute for which fixed length string is suitable?

Think of the boxes on a bank form that ask for your PIN code: exactly six boxes, no more, no fewer. Whatever your city, your PIN occupies precisely six characters. Now contrast that with the line for your name, which people fill to wildly different lengths. These are the two philosophies of storing text, and the first — a fixed number of character positions, decided in advance — is the fixed length string.

In a database table, a fixed length string column is declared with the type CHAR(n), where n is the fixed size chosen at design time. For instance:

CREATE TABLE student (
  roll_code CHAR(6),
  name      VARCHAR(30)
);

Every value stored in a CHAR(6) column occupies exactly six character positions. Store a shorter value and the database pads the remainder with spaces on the right; the stored value is always exactly six wide. Try to store a longer value and it will not fit — the column simply cannot hold a seventh character.

Its natural partner and contrast is the variable length string, VARCHAR(n), where n is only a maximum: each value occupies just the space its own characters need, and the length varies row by row.

When is fixed length the right choice? Precisely when the data itself has a fixed format:

• codes and identifiers of standard width — PIN codes, vehicle registration formats, roll-number patterns;
• single-character flags such as a gender or status code;
• any field where every legitimate value has the same known length.

For such data, CHAR is tidy and efficient: every value sits in a slot of identical size, so the storage layout is uniform and lookups are simple. The fixed width even acts as a soft check — a five-character entry in a six-character code column stands out. …