randomblob、zeroblob

実際のところ

select hex(randomblob(12));
3FEDA148FCEC829C6E9CF510

 select hex(zeroblob(16));
00000000000000000000000000000000

printf構文と組み合わせての使用も可能なので

 select printf('__%s', hex(randomblob(16)));
__11A865F3CC063DF5140C2A34EF569E16

参考もと

Built-In Scalar SQL Functions