review
1. What is the index ????
Search guide is a special data structure (B + tree)
2. Why do you need an index:
In order to speed up the search,
Principle: to reduce the number of IO by narrow your search
3. Impact of the index brings
Slower writing speed, if modified each modification will lead to rebuild the index field indexing structure
Disk usage is high
Not be able to accelerate, depends on the correct use of the sql index
4. How to use the correct reference to yesterday's summary
1. Try using a small footprint field as an index, a single table field not too much, not to store large tables of data, video, audio
2.and statement contains at least a field with index
3. Avoid using or statement, in order to speed up queries with words only if all the fields have indexes
4. Do not make the left operand arithmetic operation, to ensure that the righthand side is a fixed value
5. fuzzy query, not in front of the percent sign
6. Create a joint index, the most distinguished high on the left low of the right to put the query statement must contain an index field leftmost
7. It should be based on an index of high distinction field
8. try to ensure that the query is covered in the field, which field do not need a field which he sent another inquiry
Query plan can clearly show mysql operation to be performed, you can check out the sentence unreasonable place,
Slow query optimization, you can set a maximum execution time, if a statement execution time exceeds this maximum, this will automatically record a statement
ORM framework
ORM object-relational mapping, refers to the relationship between objects and databases
Why do Mapping? Sql statement written to avoid duplication
ORM can help us generate sql statements, execution, and get the results, in turn objects
object -> databases -> object
Hand line and ORM framework
We automatically generate those sql statement?
Create table statement
CRUD
Correspondence between the project data in the database
A project corresponds to a database
A class corresponding to a table
An object record
A field corresponding to an attribute
We want to achieve the purpose of:
When creating a class in a project automatically generates the table according to the type of information
Metaclasses to control the process of creating the class,
When we create an object and automatically generates a record based on the information of the object when you save
Object storage method to increase
When we want to modify the properties of a particular object, automatically generate a modified statement
Object provides a method to update
When you want to delete, delete the automatically generated record statement
Object provides a method to delete
When we need to get a certain type of data, automatically generating queries, and query results into objects
It provides a method for obtaining various types of objects