MySQL index and view

Mysql Index and view of

author：onceday date：2022 year 6 month 5 Japan

1. Index Overview

It is a structure that sorts the values of a single column or multiple columns in a database . Application index , Can greatly improve the speed of query .

The advantage of indexing is that you don't have to traverse the entire database , But the disadvantage is that maintaining the index requires physical space , And elapsed time .

The index will affect the insert operation of the database , When inserting data into an indexed table , The database system sorts by index .

The index generally includes B Trees (Btree) Index and hash (Hash) Indexes .

Indexes fall into the following categories :

• General index ： Indexes that do not apply any restrictions , The index can be created in any data type , The constraints of the field itself can determine whether its value is empty or unique . Users can query by index .
• Uniqueness index ： Use UNIQUE Parameter can set a unique index . When you create an index , Its value is unique , Users can quickly locate a record , A primary key is a special unique index .
• Full-text index ： Use FULLTEXT Parameter can be set to full text index . Full text index can only be created in CHAR、VARCHAR perhaps TEXT Type field on . When querying string type fields with large amount of data , Using full-text index can improve query speed . By default , Apply full-text search case insensitive . If the column of the index uses binary sorting , Execute case sensitive full-text indexing .
• Single index ： A single column index only corresponds to the index of one field , Can include common indexes , Uniqueness index , Full text index, etc . You need to ensure that the index value corresponds to a field .
• Multi column index ： Create an index on multiple fields of the table , The index points to the corresponding fields at the time of creation , Users can query through these fields . The user must use the first of these fields to apply the index .
• Spatial index ： Use SPATIAL Parameter can be set as spatial index , Spatial indexes can only be built on spatial data types , This can improve the efficiency of the system to obtain spatial data .

2. Create indexes when creating data tables

The basic syntax for creating an index when creating a data table is as follows ：

create table table_name(
 Property name   data type [ constraint condition ],
 Property name   data type [ constraint condition ]
    ......
 Property name   data type 
[UNIQUE | FULLTEXT | SPATIAL] INDEX|KEY
[ Alias ](  Property name  1 [( length )][ASC|DESC])
);

among , The attribute value after the attribute name , The meaning is as follows ：

• unique: optional , Indicates that the index is unique .
• fulltext: optional , Indicates that the index is full-text search .
• spatial: optional , Indicates that the index is a space .

index and key Parameter is used to specify the field index , Just choose one of them .

Alias as an option , Its function is to give the created index a new name .

• Property name 1： Refers to the field name corresponding to the index , The field must be pre-defined .
• length ： optional , Refers to the length of the index , Must be a string type to use .
• ASC/DESC: optional ,ASC Indicates ascending order ,DESC The parameter indicates the descending order .

2.1 General index

No need to add unique,fulltext And so on .

create table score(
id int(11) auto_increment primary key not null,
name varchar(50) not null,
math int(5) not null,
english int(5) not null,
chinese int(5) not null,
index(id));

mysql> desc score;
+---------+-------------+------+-----+---------+----------------+
| Field   | Type        | Null | Key | Default | Extra          |
+---------+-------------+------+-----+---------+----------------+
| id      | int         | NO   | PRI | NULL    | auto_increment |
| name    | varchar(50) | NO   |     | NULL    |                |
| math    | int         | NO   |     | NULL    |                |
| english | int         | NO   |     | NULL    |                |
| chinese | int         | NO   |     | NULL    |                |
+---------+-------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)

2.2 Create a unique index

Need to use unique Parameters to constrain .

create table address(
id int(11) auto_increment primary key not null,
name varchar(50),
address varchar(200),
unique index address(id asc));

mysql> show create table address;
| address | CREATE TABLE `address` (
  `id` int NOT NULL AUTO_INCREMENT,
  `name` varchar(50) DEFAULT NULL,
  `address` varchar(200) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `address` (`id`)
) ENGINE=InnoDB DEFAULT CHARSET=utf8mb3 |
1 row in set (0.01 sec)

A unique index can constrain the uniqueness of a field , But it can not improve the search speed of users .

2.3 Create full text index

The creation of full-text index can only be used in char、varchar、text Type field on . Creating a full-text index requires fulltext Parameters to constrain .

create table cards(
id int(11) auto_increment primary key not null,
name varchar(50),
number bigint(11),
info varchar(50),
fulltext key cards_info(info)) engine=MyISAM;

Be careful ： Only MyISAM Type of data table supports fulltext Full-text index ,InnoDB Or other types of data tables do not support full-text indexing .

2.4 Create a single column index

Create a single column index , That is to create an index on a single field in the data table . Creating this type of index does not require the introduction of constraint parameters , Users only need to specify a single column field name when creating .

create table telephone(
	id int(11) primary key auto_increment not null,
    name varchar(50) not null,
    tel varchar(50) not null,
    index tel_num(tel(20)));

2.5 Create multi column indexes

Specify multiple fields of the table to achieve .

create table information(
	id int(11) auto_increment primary key not null,
    name varchar(50) not null,
    sex varchar(5) not null,
    birthday varchar(50) not null,
    index info(name,sex));

In a multi column index , Only the first of these fields is used in the query criteria , Indexes are used . If you don't use the first field , Then the index doesn't work , Users want to optimize query speed , This kind of index form can be applied .

2.6 Create spatial index

Need to set up SPATIAL Parameters , Only MyISAM The type table supports this type index . Index fields must have non null constraints .

create table list(
	id int(11) primary key auto_increment not null,
    goods geometry not null,
    spatial index listinfo(goods))engine=MyISAM;

The data type corresponding to the spatial index must be the spatial data type .

3. Create an index in an established data table

It can be in the table that has been created , Create an index on one or more fields that already exist .

create [unique | fulltext | spatial] index_name
on table_name( attribute  [(length)][asc | desc]);

Parameter description ：

• index_name For index name , Give the user created index a new name .
• table_name Is the name of the watch , Specify the name of the table to create the index .
• Optional parameters , Specify the index type , Include unique（ unique index ）、fulltext( Full-text index )、spatial( Spatial index ).
• Property parameters , Specify the field name corresponding to the index . This field must already be pre stored in the data table that the user wants to operate , If the field specified by the user does not exist in the data table , The system will prompt an exception .
• length Is an optional parameter , Used to specify the index length .
• asc and desc Parameters , Specify the sort order of the data table .

3.1 Create a normal index

create index stu_info on studentinfo(sid);

3.2 Create unique index

create unique index  Index name  on  Data table name ( Field name );
create unique index index1_id on index1(cid);

3.3 Create full text index

create fulltext index  Index name  on  Data table name ( Field name )
create fulltext index index2_info on index2(info);

3.4 Create a single column index

create index  Index name  on  Data table name ( Field name ( length ));
create index index3_addr on index3(address(4));

3.5 Create multi column indexes

create index  Index name  on  Data table name ( Field name  1, Field name  2,......);
create index index4_na on index4(name,address);

It is the same as creating a multi column index when creating a data table , When creating a multi column index , The user must use the first field as the query criteria , Otherwise, the index cannot take effect .

3.6 Create spatial index

create spatial index  Index name  on  Data table name ( Field );

among ,spatial Used to set the index as a spatial index , The data table type to be operated by the user must be MyISAM type , And the field name must have a non empty constraint , Otherwise, the spatial index cannot be created normally .

4. Modify data table structure to add index

Modify the index that already exists on the table , Can pass ALTER TABLE Statement add index to data table , Its basic structure is as follows ：

alter table table_name add [unique | fulltext | spatial] index index_name( Property name  [(length)] [asc|desc]);

4.1 Add a normal index

alter table studentinfo add index timer (time(20));

4.2 Add unique index

alter table  Table name  add unique index  The index name *( Field name );

4.3 Add full text index

Full text index creation can only work on char,varchar,text Type field on .

alter table  Table name  add fulltext index  The index name ( Field name );
alter table workinfo add fulltext index index_ext(address);

4.4 Add a single column index

Creating a single column index is the same when creating a data table , You can set a single column index .

alter table  Table name  add index  The index name ( Field name ( length ));

4.5 Add multi column index

Use ALTER Modifying the data table structure can also add multi column indexes .

alter table  Table name  add index  The index name ( Field name  1, Field name 2,......);

4.6 Add spatial index

alter table  Table name  add spatial index  The index name ( Field name );

The data table type is required myIASAM type , Its field name must also have a non empty constraint .

5. Delete index

After index creation , If the user no longer needs the index , You can delete the index of the specified table .

drop index index_name on table_name;

Parameters index_name Is the index name that the user needs to delete , Parameters table_name Specify the name of the data table .

drop index index_id on workinfo;

6. Create view

6.1 Concept

The view is a virtual table , Is a table exported from one or more tables in a database , Its content is defined by query . Like a real watch , The view contains a series of named columns and rows of data .

Only the definition of view is stored in the database , There is no data in the view .

When using views to query data , The database system will take the corresponding data from the original table .

6.2 The function of view

A view works like a filter .

• simplicity ： What you see is what you need , Simplified operation , There is no need to specify all the conditions for each operation .
• Security ： View security prevents unauthorized users from viewing specific rows and columns , The method to enable authorized users to see only specific rows in the table is as follows ：
  • Add a column to the table to mark the user name
  • Create view , So that users can only see the line marked with their user name .
  • Authorize the view to other users .
• Logical data independence ： Views can make the application and database tables independent to a certain extent . Programs can be built on top of views , So the program and database tables are separated by views .

6.3 View the permission to create a view

need create view Authority , At the same time, it should have the name of the column involved in the query SELECT jurisdiction .

select Selete_priv,Create_view_priv from mysql.user where user=" user name ";

• Select_priv: Property indicates whether the user has select jurisdiction ,Y To have select jurisdiction ,N It means that there is no .
• Create_view_priv: Property indicates whether the user has create view jurisdiction ,mysql.user Express mysql Database user surface .
• “ user name ” Parameter indicates whether you want to query whether you have drop Privileged user , This parameter needs to be enclosed in single quotation marks .

select Select_priv,Create_view_priv from mysql.user where user="root";

6.4 Steps to create a view

create [algorithm = {undefined|merge|temptable}]
	view  View name [( Attribute list )]
	as select  sentence 
	[with [cascaded]local] check option];

• algorithm, Algorithm for view selection
• “ View name ” Parameters , Represents the name of the view to be created .
• “ Attribute list “, Specifies the noun for each attribute in the view , By default, it is the same as select The properties of the query in the statement are the same .
• select The statement parameter is a complete query statement , Indicates to find the records that meet the conditions from a table , Import these records into the view .
• with check option Is an optional parameter , It means that when updating a view, it must be within the permission range of the view .

Create a view in a data table ：

create view
book_view1(a_sort,a_talk,a_books)
as select sort,talk,books
from tb_book

Create views in multiple data tables ：

create algorithm=merge view
book_view1(a_sort,a_talk,a_books,a_name)
as select sort,talk,books,tb_user.name from tb_book,tb_name where tb_book.id=tb_name.id with local check option;

matters needing attention ：

1. Running the statement to create a view requires the user to have the ability to create a view (create view) Authority , If you add [or replace] when , You also need to have the ability to delete the view （drop view） Authority .
2. select Statement cannot contain from Subquery in Clause .
3. select Statements cannot reference system or user variables .
4. select Statement cannot reference preprocessing statement parameters .
5. In a stored subroutine , Definitions cannot refer to subroutine parameters or local variables .
6. The table or view referenced in the definition must exist , But after creating the view , Tables or views that define references can be discarded , It can be done by check table Check the view definition for such problems 、
7. Cannot reference... In the definition temporary surface , Can't create temporary View .
8. The table named in the view definition must already exist .
9. You cannot associate a trigger with a view .
10. Allowed in view definition order by, If the selected view has its own order by sentence , The... In the view definition will be ignored order by.

6.5 View view

The first way ：

describe  View name ;

The second way ：

desc  View name ;

The third way ：

show table status like ' View name ';

• "like" Indicates that the string is matched later ;
• “ View name ” Parameter refers to the name of the view to be viewed , Need to define with single quotation marks .

show table status like 'book_view1';

The fourth way ：

show create view  View name 
show create view book_view1;

6.6 Modify the view

The first way , You can modify a view when it exists , Create views when they don't exist .

create or replace [algorithm = {undefined|merge|temptable}]
	view  View [( Attribute list )]
	as select  sentence 
[with [cascaded|local]check option];

The second way ：

alter view [algorithm={merge | temptable|undefined}]
view view_name [(column_list)] 
as select_statement[with [cascaded | local] check option] 

• view_name： View name
• select——statement：SQL Statement is used to qualify the view .

When creating a view , In the use of the with check option,with encryption,with schemabing ,view_metadata After these functions , If you want to preserve the functionality provided by these options , Must be in alter view Include them in the statement .

6.7 Update the view

Updating a view is actually updating a table , Update view is to insert... Through view (insert)、 to update (update) And delete (delete) Table data .

When updating through a view , Must be converted to the basic table to update , And you can only update the data within your permission , Out of range , You can't update .

update book_view2 set a_book="php Typical table " where id=27;

It is best not to update data through views , Easy to fail , Many restrictions ：

1. The view contains count()、sum()、max()、min() Such as function .
2. The view contains union、union all、distinct、group by、havig Other key words .
3. Constant view
4. In the view select Contains subqueries .
5. Views exported from non updatable views .
6. When creating a view ,algorithm by temptable type .
7. There are columns without default values in the table corresponding to the view , And the column is not included in the view .

6.8 Delete view

To delete a view is to delete a view that already exists in the database . When deleting a view , You can only delete the definition of a view , Capture delete data .

have access to drop view To delete the view , The user must have drop jurisdiction .

drop view if exists < View name > [restrict | cascade]

• IF EXISTS Parameters are used to determine whether a view exists , If it exists, execute , If it does not exist, it will not execute .
• “ View name ” The list parameter indicates the name and list of the view to be deleted , The view names are separated by commas .

notes ： This content is collected on the Internet , For the purpose of study and communication only ！