varchar in mysql is a variable-length type. In a varchar type data column, each value only occupies just enough bytes, plus one byte to record its length. If the maximum length of the string column is much larger than the average length, then varchar can be used to store it.
varchar type
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varchar is variable length Type: In a varchar(M) type data column, each value only occupies just enough bytes, plus a byte used to record its length (that is, the total length is L 1 byte).
Mysql adopts a fixed width for varchar fields in memory during query instead of variable width during storage, especially the invisible temporary table created during query. Therefore, when selecting field attributes, it is better to stop and choose the most appropriate and smallest length according to your own business, thereby improving the query speed and reducing the overhead of the database server.
When to use varchar column for storage?
1. The maximum length of the string column is much larger than the average length, giving full play to the characteristics of variable length;
2. The string column is rarely updated;
Because the storage page of the innodb engine is 16k, frequent updates of variable-length fields may cause the splitting of the storage page, resulting in storage fragmentation.
3. Multi-byte character set, such as utf-8;
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