No, it is more like the compiler working out that when you say x=0 whether it should be done by loading a literal, using a zero register or xorring the register

No, it is more like the compiler working out that when you say x=0 whether it should be done by loading a literal, using a zero register or xorring the register with itself. Note that you don't actually need strong AI. Look at what MongoDB does http://docs.mongodb.org/manual/core/read-operations/#query-optimization http://docs.mongodb.org/manual/core/read-operations/#query-o... Essentially it is dumb in that it tries multiple query plans concurrently, figuring out which was most efficient and using that in the future, monitoring its expected performance and trying all candidates again when it deviates. With modern systems having such a surplus or CPU, RAM and storage a dumb system could try multiple indexing strategies, and work out which worked best.