In a relational database you normally can't.

What you do instead is use the values in the columns of the row you currently have and apply them judiciously in a WHERE clause to get the preceding or following row, based on the ORDER BY clause that you specify.

Remember that a relational database is based on set theory, so rows in a table aren't in a specific position - they are part of a set.

That said a lot of RDBMS systems have pseudo rownumber indicators (I know that Oracle has this) that you can use. It's possible that MySQL has something similar.

Michael