A question on MySQL SELECT Algorithm/Function Let's say I have 100,000 rows in a table, and each of the rows has a boolean value. Only ten of these rows have a value of 1, the rest are 0.

How would MySQL perform a SELECT on only the rows with a boolean value of 1? Would it have to do a binary search through all the values? Or would it be smart enough to pull out only the ones with a boolean value of 1 without having to search through the entire list?
To see how MySQL is doing something you want to look at the execution plan. More information on MySQL Execution plans at http://dev.mysql.com/doc/refman/5.5/en/execution-plan-information.html . You should think of SQL as a declarative language, you tell it to do something , and it writes a program to do that. The execution plan shows you the program it wrote.

SQL will be able to look up specific entries when there is an index on the column ( like an index from a book). However, a binary field with a split distribution is a classic example of a column that doesn't have good selectivity, in other words, it isn't going to narrow down the search very much.