the sqlite database table is created as:

        CREATE TABLE Books (id INTEGER PRIMARY KEY AUTOINCREMENT, path TEXT, hash blob);
        CREATE UNIQUE INDEX path_uni ON Books(path);
        CREATE UNIQUE INDEX hash_uni ON Books(hash);

and after insert some data into the database, I tried querying the “hash” column as below:

final int id = 1;
database?.query('Books', where: 'id= ?', whereArgs: [id]).then(
        (rows) {

      if (rows.isEmpty) {
          // do something...
     
      } else {
        final hash = rows.first['hash'] as Uint8List;
        print('hash: $hash'); // the printed hash is correct, 16 bytes array
        
        // use the "hash" from query result as a known existed value to do the next query:
        database?.query('Books', where: 'hash = ?', whereArgs: [hash]).then(
            (rows) {
              print('query hash: $rows'); // here print a empty list "[]"
        });
      }
    });

I can ensure all the table names and column names are correct without spelling error.
So, why is the hash-query result is empty?

I have tried use hexHash to query the database, and still get nothing back.

final String hashToCheckHex = hash.map((byte) => byte.toRadixString(16).padLeft(2, '0')).join('');
database?.query('Books', where: 'hex(hash) = ?', whereArgs: [hashToCheckHex]).then(
            (rows) {
              print('query hash: $rows'); // still get nothing.
        });