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Mysql---- import and export & View & Index & execution plan
2022-07-07 06:49:00 【An Li Jiu Ge】
Catalog
Preface
Last time I shared MySQL Function of , The content of this sharing is , Import and export 、 View 、 Index and execution plan
One 、 Import and export
1. Using tools , similar Sqlyog、Navicat Wait to import and export data .
1.1 export (Navicat)
Select the file save path
1.2 Import
Select the table , Select run SQL file
Choose SQL file
2. Use mysqldump Import and export
2.1 export
2.1.1 Export table data and table structure
mysqldump -u user name -p password Database name > Database name .sql( This name is casually called )#/usr/local/mysql/bin mysqldump -uroot -pabc >abc.sql
After typing enter, you will be prompted to output the password
notes : The exported data is in mysql Of bin Under the table of contents2.2 Import
Be careful : First, create an empty database
mysql>create database abc;
2.2.1 Method 1
mysql>use abc; # Select database
mysql>set names utf8; # Set database encoding
mysql>source /home/abc/abc.sql; # Import data2.2.2 Method 2
mysql -u user name -p password Database name < Database name .sql
#mysql -uabc_f -p abc < abc.sql
3.LOAD DATA INFILEYou can go through first SELECT INTO OUTFILE The way , Export data to Mysql Of C:\ProgramData\MySQL\MySQL Server 5.5\data Under the table of contents , Re pass LOAD DATA INFILE Mode import .
1) select * from Table name into outfile '/ file name .sql';
2) load data infile '/ file name .sql' into table Table name ( Name 1,...);Be careful : Authorization is required, otherwise it cannot be exported successfully
In our MySQL Under the installation directory of my.ini Authorization in document
Two 、 View
1. What is a view
1) A view is a virtual table , A table derived from one or more tables in a database .
2) The definition of view is stored in the database , There is no data stored in view , The data is stored in the original table .
3) When using views to query data , The database system will take the corresponding data from the original table .
2. The function of view1) Make the operation simple .
2) Increase data security .
3) Improve the logical independence of tables .3. Basic grammar
CREATE VIEW View name AS SELECT sentence ;Be careful : On the premise of successful view creation, duplicate columns cannot appear
3、 ... and 、 Indexes
1. What is index
An index is a combination of one or more columns in a database table , Its function is to improve the query speed of data in the table .
A catalogue similar to a book , Easy and fast positioning , Find the specified content .2. Advantages and disadvantages of index
advantage : Speed up data query .
shortcoming : The time to create and maintain indexes has increased , At the same time, it takes up hard disk space .3. Index classification
1) General index : Is the most basic index , It has no restrictions ;
Be careful : The corresponding column values of unique key indexes are not allowed to be the same
2) unique index : Similar to the previous normal index , The difference is that : The value of the index column must be unique , But you can have an empty value . If it's a composite index , The combination of column values must be unique ;
3) primary key : Is a special unique index , A table can only have one primary key , No null values are allowed ;
4) Composite index : An index created on multiple fields , Only the first field that created the index is used in the query criteria , Indexes are used . When using a composite index, follow the leftmost prefix set ;
Follow the leftmost segment matching principle
5) Full-text index : Use FULLTEXT Parameters can be set , Full text index can only be created in CHAR,VARCHAR,TEXT Type field on . The main function is to improve the speed of querying larger string types ; Only MyISAM The engine supports the index ,MySQL The default engine does not support ;mysql5.7+
Word segmentation is The Chinese / the people / republic
4. Create index
CREATE [UNIQUE|FULLTEXT] INDEX Index name ON Table name ( Field name [( length )][ASC|DESC])
5. Modify the index
ALTER TABLE Table name ADD [UNIQUE|FULLTEXT] INDEX Index name ( Field name [( length )][ASC|DESC])
6. Delete index
DROP INDEX Index name ON Table name
Four 、 Implementation plan
We import case data
explain select * from t_user u left join t_role r on u.roleid = r.roleid
explain select * from t_user u where u.roleid = (select roleid from t_role where rolename = ' Administrators ')
explain select * from t_user u left join t_role r on u.roleid = r.roleid
explain select * from t_user u right join t_role r on u.roleid = r.roleid
id The higher the priority, the higher
1、 like Key left cannot be added %
2、or The conditional column segment of a link cannot be a column segment without an index
3、 The data type of query criteria must be a value
4、 Avoid using !=
5、 Sorting will invalidate the index
6、 The leftmost paragraph implements the principle
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