Difference in mysql dump file size and database size

The dump file is a text file. When you turn the internal data of a DB into text, there are many expansions:

• Numbers that might be 4 bytes internally are written out as digits like 123456
• Strings have quotes around them, and special characters in the strings may be escaped
• There are commas between each column, and parentheses around the rows

When you run mysqldump, only data is dumped in SQL statements. Indexed are not copied. Indexes get rebuilt when the SQL is loaded into another server.

For a good normalized db, db size is significantly smaller than dump file.

Because the db uses a lot of numbers, I have a db with 200 mb dump, but only 80 kb in db.

As said by Barmar, during dump, numbers are converted into characters, 1234567891 uses 1 integer for storage, or 3 bytes, but 10 bytes for the characters.