With just SQL you aren't going to be making very meaningful formulas by level, and EQ doesn't really pay much attention to level after 45.
For your purposes you might do something like
UPDATE npc_types SET ac = ac / 2
UPDATE npc_types SET mindmg = mindmg / 2
Use the existing scaling and ignore levels so when you get to a special boss encounter they are still harder than a regular mob of their level elsewhere, just not as hard as they are on live.
For items you might do something like
UPDATE items SET dex = dex * 2 WHERE dex > 0
If you want to add additional related stats you might run something like
UPDATE items SET agi = dex WHERE dex > 0
UPDATE items SET haste = 30 WHERE agi > 15 AND haste < 30
UPDATE items SET mana = 300 WHERE int > 10 AND mana < 300
UPDATE items SET hp = 300 WHERE (sta > 10 OR str > 10) AND hp < 300
For better mysql documentation, go straight to the source.
http://dev.mysql.com/doc/