Ordinary Index: basic index
Composite index: the index built on multiple fields
The only index: Similar to the general index, the only index column value can be null
The only composite index: must be unique
Primary key index: Special unique index can not be null
Full-text index: Query for mass text
Index optimization, sql optimization: The index does not include null columns, use short index, the index column sorting, like statement operation, not to carry out operations in the column
Index creation: create index index name on table
Unique index: create unique index index name on table