[MySQL learning notes 24] index design principles

1. Only when there is a large amount of data can the index be established , Otherwise, the effect is not obvious . A few w The index is not improved much when the index is changed , To dozens w The article will be improved , But it's not too big , A few hundred w Thousands of w There is a big difference between using an index and not using an index .
2. If the query frequency is not high , There's no need to index
3. Index the query criteria
4. Try to select the field with high discrimination as the index , It doesn't make sense to use gender as a field , It is no different from full table query . The unique index discrimination is the highest , Because unique indexes force field values to be unique
5. Try to use a union index , Reduce single column index , Try to overwrite the index when querying , Avoid back table queries
6. Reasonably control the number of indexes , More indexes is not better , Too many will affect the efficiency of addition, deletion and modification .
7. If the index column cannot store null value , Please use... When creating the table not null constraint . When the optimizer knows whether each column contains null When the value of , It can better select indexes .