Why are BLOBs with same data treated as different?
When you run a statement with DISTINCT or GROUP BY clause you might notice that each BLOB is treated as a different value, even if the value in BLOB field is the same.
This is because BLOBs are sorted by their IDs and not their content. Idea behind this is that BLOB data is usually huge, so comparing it would be an expensive operation.
If you still need grouping, you can cast initial BLOB characters to VARCHAR type and compare that. You are limited by VARCHAR size for the character set that is used (about 32000 bytes in total).