A jar with a single key inside has its lid closed shut. How can you get the key out? The jar is glued to the table, and the lid is stuck as well. Your solution should be quick (a minute max).
Jars are known to shatter when dropped from a certain height, which is probably why the OP included that the jar is glued to the table. The OP didn't say that the table is glued to the ground, so my guess is to lift the table upside-down, and drop it.
For those who would like a clearer example, here is a tutorial: