[MySQL] index creation, viewing and deletion

One 、 Create index

1、 Create indexes while creating tables

Use create table Create table time , In addition to defining the data type of the column , You can also define primary key constraints Foreign key constraints Or uniqueness constraint , No matter what kind of constraint you create , While defining the constraint, it is equivalent to creating an index on the specified column .

① Create a normal index

CREATE TABLE book(
book_id INT ,
book_name VARCHAR(100),
AUTHORS VARCHAR(100),
info VARCHAR(100) ,
COMMENT VARCHAR(100),
year_publication YEAR,
# Declaration index 
INDEX idx_bname(book_name)
);

② Create a unique index

Declare a field with a unique index , When adding data , Make sure it's unique , But you can add null
Keywords of unique index ：unique

CREATE TABLE book1(
book_id INT ,
book_name VARCHAR(100),
AUTHORS VARCHAR(100),
info VARCHAR(100) ,
COMMENT VARCHAR(100),
year_publication YEAR,
# Declaration index 
UNIQUE INDEX uk_idx_cmt(COMMENT)
);

③ Create primary key index

After setting it as the primary key, the database will automatically create an index ,innodb Index for clustering , grammar ：
keyword :PRIMARY KEY

# Define the primary key index by defining the primary key constraint 
CREATE TABLE book2(
book_id INT PRIMARY KEY ,
book_name VARCHAR(100),
AUTHORS VARCHAR(100),
info VARCHAR(100) ,
COMMENT VARCHAR(100),
year_publication YEAR
);

Be careful ： Delete primary key index ： Delete the primary key index by deleting the primary key constraint

ALTER TABLE book2
DROP PRIMARY KEY;

Modify the primary key index ： You must delete (drop) The original index , New again (add) Indexes

④ Create a single column index

CREATE TABLE book3(
book_id INT ,
book_name VARCHAR(100),
AUTHORS VARCHAR(100),
info VARCHAR(100) ,
COMMENT VARCHAR(100),
year_publication YEAR,
# Declaration index 
UNIQUE INDEX idx_bname(book_name)
);

⑤ Create a federated index

CREATE TABLE book4(
book_id INT ,
book_name VARCHAR(100),
AUTHORS VARCHAR(100),
info VARCHAR(100) ,
COMMENT VARCHAR(100),
year_publication YEAR,
# Declaration index 
INDEX mul_bid_bname_info(book_id,book_name,info)
);

⑥ Create full text index

fulltext Full text index can be used for full-text search , And only for char varchar and text Column creation index .
The index is always on the entire column , Local is not supported （ Prefix ） Indexes .

CREATE TABLE test4(
id INT NOT NULL,
NAME CHAR(30) NOT NULL,
age INT NOT NULL,
info VARCHAR(255),
FULLTEXT INDEX futxt_idx_info(info(50))
# info(50) Belong to local （ Prefix ） Indexes , Currently does not support , Only the current column will be searched 
)

Full text indexes can create multiple columns

CREATE TABLE articles (
  id INT UNSIGNED AUTO_INCREMENT PRIMARY KEY, 
  title VARCHAR (200),
  body TEXT, 
  FULLTEXT index (title, body) 
) ENGINE = INNODB ;

tips： For fuzzy query

like How to query ：

SELECT * FROM papers WHERE content LIKE ‘% Query string %’;

Full text citation match+against Mode query ：

SELECT * FROM papers WHERE MATCH(title,content) AGAINST (‘ Query string ’);

Be careful
1. Before using full-text indexing , Find out the version support ;
2. Full text index ratio like + % fast N times , But there may be precision problems ;
3. If you need a large amount of data for full-text indexing , It is recommended to add data first , Then create the index .

⑦ Create spatial index

The spatial index is being created , The required field of space type must be Non empty .
give an example ： Create table test5, The space type is GEOMETRY Create a spatial index on the field of ,SQL The statement is as follows :

CREATE TABLE test5( 
  geo GEOMETRY NOT NULL, 
  SPATIAL INDEX spa_idx_geo(geo) 
) ENGINE=MyISAM;

2、 Create an index on the created table

To create an index in an existing table, you can use ALTER TABLE Statements or CREATE INDEX sentence .

① Use alter table Statement to create an index

Basic grammar ：alter table …add…

# Create data table 
CREATE TABLE book5(
book_id INT ,
book_name VARCHAR(100),
AUTHORS VARCHAR(100),
info VARCHAR(100) ,
COMMENT VARCHAR(100),
year_publication YEAR
);

#  Create index  alter table ...add...
#  General index 
ALTER TABLE book5 ADD INDEX idx_cmt(COMMENT);
#  Uniqueness index 
ALTER TABLE book5 ADD UNIQUE uk_idx_bname(book_name);
#  Joint index 
ALTER TABLE book5 ADD INDEX mul_bid_bname_info(book_id,book_name,info);

② Use create index Create index

Basic grammar ：create index…on…

CREATE INDEX Statement can add an index to an existing table , stay MySQL in , CREATE INDEX Mapped to a ALTER TABLE On statement , The basic grammatical structure is ：

#  Create data table 
CREATE TABLE book6(
book_id INT ,
book_name VARCHAR(100),
AUTHORS VARCHAR(100),
info VARCHAR(100) ,
COMMENT VARCHAR(100),
year_publication YEAR
);

#  Create index  create index...on....
#  General index 
CREATE INDEX idx_cmt ON book6(COMMENT);
#  Uniqueness index 
CREATE UNIQUE INDEX  uk_idx_bname ON book6(book_name);
#  Joint index 
CREATE INDEX mul_bid_bname_info ON book6(book_id,book_name,info);

Two 、 Look at the index

View the index through the command
Mode one ：

SHOW CREATE TABLE book;

Mode two ：

SHOW INDEX FROM book;

3、 ... and 、 Delete index

1、 Use ALTER TABLE Delete index

ALTER TABLE The basic syntax for deleting an index is as follows ： ALTER TABLE … DROP INDEX …

ALTER TABLE book5 
DROP INDEX idx_cmt;

Tips ： add to Auto_increment（ Self growth ） The unique index of the constraint field cannot be deleted

2、 Use DROP INDEX Statement to delete the index

DROP INDEX The basic syntax for deleting an index is as follows ： DROP INDEX … ON …

DROP INDEX uk_idx_bname ON book5;

tips： Delete related fields in the federated index （ Delete the fields in the table ）

Delete related fields in the federated index

ALTER TABLE book5
DROP COLUMN book_name;

Tips ： When deleting columns in a table , If the column to be deleted is part of the index , The column is also removed from the index . If all the columns that make up the index are deleted , Then the entire index will be deleted .