SQLite database operation

1. Table creation SQL

/**
 CREATE TABLE  --  Table creation 
 IF NOT EXISTS --  Determine whether the data table exists , If there is , No more table creation  SQL
 'T_Person'    --  Table name  
 （
    Field 1 INTEGER( Integers )/REAL( decimal )/TEXT( character string )/BLOB( binary data - Usually not saved in the database )
	       NOT NULL         Not allowed to be empty , The primary key must have content 
				 PRIMARY KEY      Primary key 
				 AUTOINCREMENT    Automatic growth 
				 ,                Distinguish each field , The last field doesn't need to be  ‘,’
				  Field 2  type 
				 ...
  ）
	 Use :
	1. source , You can copy and paste 
	2. Single quotation marks are recommended , It can avoid translating in the program 
	3.IF NOT EXISTS  It needs to be added separately , In order to ensure  SQL  Statements can be repeatedly executed ！
	4. Every  SQL  At the end of the statement , It is suggested to add a ';'  It means a complete  SQL  end 
*/

CREATE TABLE IF NOT EXISTS 'T_Person' (
  "id" INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT,
  "name" TEXT,
  "age" INTEGER,
  "height" NUMBER
);

2. Insert SQL

/**
INSERT INTO ‘ Table name ’
  ( Field 1,  Field 2, ...)
	VALUES
	( value 1,  value 2, ...)
	
	 Be careful :
	1. The order of fields and values must be consistent 
	 Tips :
	SQLite  Data types are essentially indistinguishable , Save whatever you want , When defining the table structure , The specified type is just decoration 
	 It is recommended to store by type 
*/

INSERT INTO T_Person
(name,age,height)
VALUES
(' Little love ',22,1.55);

3. Delete SQL

/**
  DELETE FROM ' Table name '
	WHERE  Primary key  = id 
	 Be careful : 
	     Delete statements must be written  WHERE!  Otherwise, all data will be deleted !
	     If the specified condition does not exist ,SQL  Will execute , But the number of affected lines is 0
*/

DELETE FROM T_Person
WHERE id = 2000;

4. to update SQL

/**
UPDATE ‘ Table name ’
SET
	 Field 1 = ‘ A string value 1’,
	 Field 2 =   value 2
	...
	WHERE( Conditions )
	 Primary key  = id;
	
	 Tips :
	 Be sure to write conditions , Otherwise, all records will be modified 
	 If the specified condition does not exist ,SQL  Will execute , But the number of affected lines is 0
*/

UPDATE T_Person SET name = ' Lao Wang ',age = 28, height = 1.76
WHERE id = 1000

5. Inquire about SQL

--  Check all records , however ： It is not recommended to write  *  wildcard , Reading the code directly cannot know the content returned by the query 
--  It can be used in testing , In program code , Not recommended 
SELECT * FROM T_Person;

--  Recommended for development , Easy to read  
SELECT id, name, height, age FROM T_Person;

--  Statistics query 
SELECT COUNT(*) FROM T_Person;

--  Specify conditional statistics query 
SELECT COUNT(*) FROM T_Person WHERE height > 1.7;

--  Ask the oldest person 
--  Application scenarios :  The highest value of query experience , People who recently joined ...
SELECT MAX(age) FROM T_Person;

--  Paging function 
-- LIMIT  Start with the record ( The starting number is : 0), The number of record rows returned 
SELECT id, name, height, age FROM T_Person
LIMIT 0, 2;

-- LIMIT  And conditional instructions  WHERE  Use a combination of , You can easily make paging function 
SELECT id, name, height, age FROM T_Person
WHERE id >= 8
LIMIT 2;

--  Sorting function ,  Default ascending order  ASC /  Descending  DESC
--  Sorting is based on specified conditions , Sort from left to right 
SELECT id, name, height, age FROM T_Person
ORDER BY name DESC, age ASC;

--  Fuzzy query 
-- %  Can match anything 
-- % Content %  It means that as long as the content appears , Will be searched out 
--  logic  AND OR NOT 
SELECT id, name, height, age FROM T_Person
WHERE (name LIKE '% king %' AND age > 18) OR name LIKE ' Zhang dada ';