Table Sizes / Num Records vs. Performance?

[superwormy]

MySQL specifically, but it probably applies to other databases as well.

Say you had a large number of records in a single table, like 500,000 records AS OPPOSED TO 5x 100,000 record tables.
Assuming it wasn't much more overhead to determine which table to select from, will the selects from the smaller tables be faster?

I guess the bottom line question is, as teh number of records grows, will performance decrease in the table?

[nnichols]

Performance will decrease - it will always take longer to sift through 1,000,000 records than 10,000 records. But it shouldn't be that significant if the hardware is up to the job and the tables are well indexed.