UNCOMPRESSED_LENGTH(compressed_string) returns the length that the compressed string had before being compressed. : UNCOMPRESSED_LENGTH « Encryption Compression Functions « MySQL Tutorial

1. MySQL Tutorial
2. Encryption Compression Functions
3. UNCOMPRESSED_LENGTH

mysql>
mysql>
mysql> SELECT UNCOMPRESSED_LENGTH(COMPRESS(REPEAT('a',30)));
+-----------------------------------------------+
| UNCOMPRESSED_LENGTH(COMPRESS(REPEAT('a',30))) |
+-----------------------------------------------+
|                                            30 |
+-----------------------------------------------+
1 row in set (0.00 sec)

mysql>
mysql>