MySQL interview questions

mysql The scenario of index creation and the problem of index invalidation ?

MySQL The scenarios for indexing are

1. Create an index for fields with high query frequency ;
2. Sort 、 grouping 、 Index fields with high query frequency ;
3. If you need to set multiple columns as indexes , You can use a multi column index
4. Select a unique index and try to use an index with less data

The reason for index failure

1. Function parameters or expressions appear in the index column

Solution ： Calculate the value of the expression in advance

2. Use left blur

Solution ： Try to avoid

3. Use OR Some fields of the query have no index

Solution ：or Add an index to the field

4. No single quotation marks

surface 1: Person

+-------------+---------+

| Name | type |

+-------------+---------+

| PersonId | int |

| FirstName | varchar |

| LastName | varchar |

+-------------+---------+

PersonId Is the primary key of the above table

surface 2: Address

+-------------+---------+

| Name | type |

+-------------+---------+

| AddressId | int |

| PersonId | int |

| City | varchar |

| State | varchar |

+-------------+---------+

AddressId Is the primary key of the above table

 

Write a SQL Inquire about , Meet the conditions ： No matter what person Is there address information , Both need to be provided based on the above two tables  person For ：