Let's say you have this data:
ID, FName, LName, DOB
1, John, Smith, 1/1/1990
2, Sally, Jones, 2/2/1981
3, Pete, Davis, 3/3/1992
4, Ron, Bush, 4/4/1983
As typed it the "middle" is between ID 2 & 3. But if you open it and its sorted by:
FName, the "middle" is between John (ID=1) & Pete (ID=3)
LName, the "middle" is between Davis (ID=3) & Jones (ID=2)
DOB, the "middle" is between 4/4/1983 (ID=4) & 1/1/1990 (ID=1)
A table never has a middle, because a table is just a big bucket you throw data into. Order exists in it only when you explicitly define that order via query with an ORDER BY clause. So perhaps you can explain your situation better and what you actually hope to accomplish. What will "inserting into the middle of the table" help you actually achieve?