SQL advanced syntax

Insert data one

INSERT INTO tab_name (col_name) VALUES ( The data to be inserted , Here is the first line of data ), ( The data to be inserted , Here is the second line of data )…( The data to be inserted , The first n Row data )

Example ： Insert two users' test papers to answer exam_record In the table ,
（1） user 1001 stay 2021 year 9 month 1 On Tuesday night 10 spot 11 branch 12 Begin to answer the test paper in seconds 9001, And in 50 Submit in minutes , got 90 branch ;
（2） user 1002 stay 2021 year 9 month 4 The morning of 7 spot 1 branch 2 Begin to answer the test paper in seconds 9002, And in 10 Minutes later, he exited the platform .（ Be careful , user 1002 Failed to complete the examination paper , therefore submit_time and score The values of the two columns are null）

 Method 1 ： Specify insert column name 
INSERT INTO exam_record (uid, exam_id, start_time, submit_time, score) VALUES
(1001, 9001, '2021-09-01 22:11:12', '2021-09-01 23:01:12', 90),
(1002, 9002, '2021-09-04 07:01:02', NULL, NULL)
 Method 2 ： hold id Is set to null or 0, Give Way mysql Self increasing 
INSERT INTO exam_record VALUES
(NULL, 1001, 9001, '2021-09-01 22:11:12', '2021-09-01 23:01:12', 90),
(NULL, 1002, 9002, '2021-09-04 07:01:02', NULL, NULL)
 Method 3 ： Fill in directly id value 
INSERT INTO exam_record VALUES
(1, 1001, 9001, '2021-09-01 22:11:12', '2021-09-01 23:01:12', 90),
(2, 1002, 9002, '2021-09-04 07:01:02', NULL, NULL)

Insert data 2

Insert method summary ：

1、 Normal insert （ Full field ）：INSERT INTO table_name VALUES (value1, value2, …)
2、 Normal insert （ Restricted field ）：INSERT INTO table_name (column1, column2, …) VALUES (value1, value2, …)
3、 Multiple one-time inserts ：INSERT INTO table_name (column1, column2, …) VALUES (value1_1, value1_2, …), (value2_1, value2_2, …), …
4、 Import from another table ：INSERT INTO table_name(column1, column2, …) SELECT (column1, column2, …) FROM table_name2 [WHERE key=value]

Topic 1 ： Do data backup , take exam_record In the table 2021 Back up the contents of years ago to exam_record_before_2021 In the table .

insert into exam_record_before_2021(uid, exam_id, start_time, submit_time, score)
select uid, exam_id, start_time, submit_time, score from exam_record
where year(submit_time)<'2021'

Topic two ： There is a set ID by 9003 High difficulty SQL The examination paper , For an hour and a half , Need to put 2021-01-01 00:00:00 Insert it into the test question information table as the release time , No matter ID Whether it exists or not must be inserted successfully .

Method 1 ： Use replace into.replace into First try inserting the data list , If you find that this row of data already exists in the table , Delete this row of data first , Then insert the new data , Otherwise, insert new data directly .

replace into examination_info values
(null,9003,'SQL','hard',90,'2021-01-01 00:00:00')

Method 2 ： Use insert into, But need （delete） The priority of deleting user name is 9003 The data of .

delete from examination_info 
where exam_id=9003;
insert into examination_info 
values(null,9003,'SQL','hard',90,'2021-01-01 00:00:00')

Update data one

Modification method summary ：

1、 Set to new value ：

UPDATE table_name 
SET column_name=new_value
WHERE column_name3=value3

 for example , take tag Field PYTHON To Python：
update examination_info
set tag='Python'
where tag='PYTHON'

2、 Replace... With existing values ：( It can be replaced by the whole string Substring substitution ！)

UPDATE table_name 
SET key1=replace(key1, ' Find content ', ' Replace with the content ') 
WHERE column_name3=value3

 for example , take tag Field PYTHON To Python：（ Whole string replacement ）
update examination_info
set tag=replace(tag,"PYTHON","Python")
where tag='PYTHON'

 Substring substitution , take APYTHON Replace with APython：
update examination_info
set tag=replace(tag,"PYTHON","Python")
where tag like "%PYTHON%"

Delete record

Deletion method summary ：

1、 Delete... According to conditions ：

DELETE FROM tb_name 
WHERE options
ORDER BY fields LIMIT n 

2、 Delete all （ The watch is empty , Including self incrementing counter reset ）：

TRUNCATE tb_name

Cattle guest . SQL8 Delete record 3

Be careful , Use delete from Deleting a table requires manual auto increment ID, In terms of efficiency , Or delete all （TRUNCATE tb_name） More efficient . Last time I used delete from The solution of deletion is ：

delete from exam_record;
alter table exam_record auto_increment=1;

Create a new table

The operation of the table ： establish 、 modify 、 Delete .

1、 Create tables directly
Cattle guest . SQL9 Create a new table
2、 Copy the table structure from another table to create a table
3、 Create a table from the query results of another table
4、 Modify table

{ ADD COLUMN < Name > < type >  --  Add column 
 | CHANGE COLUMN < Old column names > < New column names > < New column type > --  Modify the column name or type 
 | ALTER COLUMN < Name > { SET DEFAULT < The default value is > | DROP DEFAULT } --  modify / Delete   Default value of column 
 | MODIFY COLUMN < Name > < type > --  Modify column type 
 | DROP COLUMN < Name > --  Delete column 
 | RENAME TO < The new name of the table > --  Modify the name of the table 
 | CHARACTER SET < Character set name > --  Modify character set 
 | COLLATE < Proofreading rule name > } --  Modify proofreading rules （ When comparing and sorting ）

Cattle guest . SQL10 Modify table
5、 Delete table

drop table if exists  Table name 1, Table name 2....

Cattle guest . SQL11 Delete table

Index creation and deletion

Index creation 、 Delete 、 Use ：

1、create How to create an index

CREATE INDEX  Index name  ON  Table name ( Name );  -- If you do not specify a unique or full-text index, it defaults to normal index 
CREATE UNIQUE INDEX  Index name  ON  Table name ( Name );  -- unique index 
CREATE FULLTEXT INDEX  Index name  ON  Table name ( Name );  -- Full-text index 

Cattle guest . SQL12 Create index

2、alter How to create an index

alter Basic format of index creation ：

alter table  Table name  add unique index  Index name ( Name );  -- unique index 
alter table  Table name  add fulltext  Index name ( Name );    -- Full-text index 
alter table  Table name  add index  Index name ( Name );   -- If you do not specify a unique or full-text index, it defaults to normal index 

3、drop To delete the index

DROP INDEX < Index name > ON < Table name >

Cattle guest . SQL13 Delete index

 Cattle guest . SQL13  Delete index :
DROP INDEX uniq_idx_exam_id ON examination_info;
DROP INDEX full_idx_tag ON examination_info;

4、alter To delete the index

ALTER TABLE < Table name > DROP INDEX < Index name >

 Cattle guest . SQL13  Delete index :
alter table examination_info drop index uniq_idx_exam_id;
alter table examination_info drop index full_idx_tag;

Aggregate group query

Cattle guest . SQL16 Not less than the lowest score of the average

Cattle guest . SQL17 Average number of active days and monthly number of active people

SUBSTR(str,pos,len):  from pos Starting position , Intercept len Characters .
SUBSTR(str,pos): pos Starting position , Cut it all the way to the end .

Multi-table query

Cattle guest . SQL45 Intercept the long nickname

length function ： Calculate the length of the value , but 1 Chinese will count as length 3,1 Numbers or letters count as length 1;
char_length function ： Calculate the length of the value , but 1 Chinese or 1 Numbers or letters count as length 1;