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.open filename -- Open file 
--  annotation 
.show -- Show SQLite  The default setting of the command prompt 
.q -- sign out 
.databases -- Display database （ notes ： Show open databases ）
.help  -- help 
.dump  -- Import export database 
.tables  -- See the table

2. data type

Storage type

describe

NULL

Null value

int

plastic

text

A text string

blob

One blob data

integer

A signed integer , According to the size of the value stored in １、２

、３、４、６ or ８ In bytes

real

Value is a floating point value , Stored as ８ Floating point number of bytes

…

３． Create database

.open test.db -- Create without 
sqlite3 DatabaseName.db

The above command will create a file in the current directory testDB.db. The file will be deleted SQLite The engine acts as a database . If you have noticed sqlite3 Command after successfully creating the database file , A will be provided sqlite> Prompt .

.databases The command is used to check whether it is in the database list .

.open operation

4. Import / Export database

sqlite3 test.db .dump　> filename -- export 
sqlite3 test.db < filename -- Import

The above transformation flows through testDB.db The contents of the database to SQLite The statement of , And dump it to ASCII text file testDB.sql in . You can generate from the in a simple way testDB.sql recovery , As shown below I'll delete it testDB.db after ：

5. Create table

-- Be careful , You can only operate when you open the database 
CREATE TABLE database_name.table_name(
   column1 datatype  PRIMARY KEY(one or more columns),
   column2 datatype,
   column3 datatype,
   .....
   columnN datatype,
);

CREATE TABLE Is a keyword that tells the database system to create a new table .CREATE TABLE Statement followed by the unique name or ID of the table . You can also choose to specify with table_name Of database_name.

As shown in the figure above , We created COMPANY DEPARTMENT Two tables . among ID A primary key ,NOT NULL The constraint of indicates that these fields cannot be... When creating records in the table NULL.

６． See table details

.schema -- Be careful ： Only when the database is opened

７． Delete table

DROP TABLE database_name.table_name;

Above , Deleted the name DEPARTMENT Table of

８. insert data

INSERT INTO TABLE_NAME [(column1, column2, column3,...columnN)]  
VALUES (value1, value2, value3,...valueN);

ad locum ,column1, column2,…columnN Is the name of the column in the table to insert data .

If you want to add values to all columns in the table , You may also not need to be in SQLite Specify the column name... In the query . But make sure that the values are in the same order as they are listed in the table .SQLite Of INSERT INTO The grammar is as follows ：

INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN);

Now? , I have created COMPANY surface , as follows

CREATE TABLE COMPANY(
   ID INT PRIMARY KEY     NOT NULL,
   NAME           TEXT    NOT NULL,
   AGE            INT     NOT NULL,
   ADDRESS        CHAR(50),
   SALARY         REAL
);

Now? , The following statement will be in COMPANY Create six records in the table ：

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (1, 'Paul', 32, 'California', 20000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (2, 'Allen', 25, 'Texas', 15000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (5, 'David', 27, 'Texas', 85000.00 );

INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)
VALUES (6, 'Kim', 22, 'South-Hall', 45000.00 );

The output is as follows ：

We can also use the second grammar in COMPANY Create a record in the table , As shown below ：

INSERT INTO COMPANY VALUES (7, 'James', 24, 'Houston', 10000.00 );

The output is as follows ：

９. Format output

.header on
.mode column
.timer on　-- Turn on ＣＰＵ Timer 
SELECT * FROM table_name;　-- Display table table_name

Unformatted output

Format output

１０． Output table

Full output

.header on
.mode column
SELECT * FROM COMPANY;

Output specified column

.header on
.mode column
SELECT ID, NAME, SALARY FROM COMPANY;　-- Only the output ID, NAME and SALARY The three column

Set the width of the output column

.width num1,num1,num3....
SELECT * FROM COMPANY;

below .width The command sets the width of the first column to 10, The width of the second column is 20, The width of the third column is 10. The output is as follows ：

１１． Operator

sqlite The operator is mainly used for SQLite Of the statement WHERE Clause , Such as comparison and arithmetic operation .

Operator is used to specify SQLite The condition in the statement , And connect multiple conditions in the statement .

Arithmetic operator ：

Operator

describe

example

Add - Add the values on both sides of the operator

a + b Will get 30

Subtraction - Subtract the right operand from the left operand

a - b Will get -10

Multiplication - Multiply the values on both sides of the operator

a * b Will get 200

division - Left operand divided by right operand

b / a Will get 2

modulus - The remainder of the left operand divided by the right operand

b % a will give 0

Comparison operator

Operator

describe

example

Check that the values of the two operands are equal , If they are equal then the condition is true .

(a == b) Not true .

Check that the values of the two operands are equal , If they are equal then the condition is true .

(a = b) Not true .

Check that the values of the two operands are equal , If they are not equal then the condition is true .

(a != b) It's true .

Check that the values of the two operands are equal , If they are not equal then the condition is true .

(a <> b) It's true .

Check whether the value of the left operand is greater than the value of the right operand , If so, the condition is true .

(a > b) Not true .

Check whether the value of the left operand is less than the value of the right operand , If so, the condition is true .

(a < b) It's true .

Check whether the value of the left operand is greater than or equal to the value of the right operand , If so, the condition is true .

(a >= b) Not true .

Check that the value of the left operand is less than or equal to the value of the right operand , If so, the condition is true .

(a <= b) It's true .

Check whether the value of the left operand is not less than the value of the right operand , If so, the condition is true .

(a !< b) For false .

Check that the value of the left operand is not greater than the value of the right operand , If so, the condition is true .

(a !> b) It's true .

Logical operators

Operator

describe

AND

AND Operator is allowed in a SQL Of the statement WHERE The existence of multiple conditions in the clause .

BETWEEN

BETWEEN Operator is used to search for a value in a series of values within a given range of minimum and maximum values .

EXISTS

EXISTS Operator is used to search for the existence of rows in the specified table that meet certain conditions .

IN Operator is used to compare a value with a series of values in a specified list .

NOT IN

IN The opposite of operator , Used to compare a value with a value that is not in a series of specified lists .

LIKE Operator is used to compare a value with a similar value using the wildcard operator .

GLOB

GLOB Operator is used to compare a value with a similar value using the wildcard operator .GLOB And LIKE The difference is , It's case sensitive .

NOT

NOT The operator is the opposite of the logical operator used . such as NOT EXISTS、NOT BETWEEN、NOT IN, wait . It is a negative operator .

OR Operator is used to combine a SQL Of the statement WHERE Multiple conditions in clause .

IS NULL

NULL Operator is used to associate a value with NULL Value comparison .

IS Operators and = be similar .

IS NOT

IS NOT Operators and != be similar .

Connect two different strings , Get a new string .

UNIQUE

UNIQUE Operator to search each row in the specified table , Make sure it's unique （ No repetition ）.

An operator

p & q

p | q

The following is a direct example

I have a COMPANY The table is as follows ：

ID          NAME        AGE         ADDRESS     SALARY
----------  ----------  ----------  ----------  ----------
1           Paul        32          California  20000.0
2           Allen       25          Texas       15000.0
3           Teddy       23          Norway      20000.0
4           Mark        25          Rich-Mond   65000.0
5           David       27          Texas       85000.0
6           Kim         22          South-Hall  45000.0
7           James       24          Houston     10000.0

use SELECT List SALARY Greater than 50,000.00 All records ：

SELECT * FROM COMPANY WHERE SALARY > 50000;

The output is as follows ：

use SELECT List SALARY Equal to all records of ：

SELECT * FROM COMPANY WHERE SALARY = 20000;

The output is as follows ：

use SELECT List AGE Greater than or equal to 25 And SALARY Greater than or equal to 65000.00 All records ：

SELECT * FROM COMPANY WHERE AGE >= 25 AND SALARY >= 65000;

The output is as follows ：

12.where Clause

SQLite Of WHERE Clause is used to specify the conditions for getting data from one or more tables . If a given condition is satisfied , It's true （true） when , Returns a specific value from the table . You can use WHERE Clause to filter records , Just get the records you need .WHERE Clause can be used not only in SELECT In the sentence , It can also be used in UPDATE、DELETE In the sentence , wait . Use case reference operators .

13. Delete the data in the record table

SQLite in , Delete record table data as DELETE sentence , We can use it with WHERE Clause DELETE.

The grammar is as follows ：

DELETE FROM table_name　WHERE [condition];

We have the following record sheet ：

Delete ID by ７ The column of ：

DELETE FROM COMPANY WHERE ID = 7;

Output the result again ：

14.update sentence

SQLite Of UPDATE Queries are used to modify existing records in a table . You can use the WHERE Clause UPDATE Query to update the selected row , Otherwise, all the lines will be updated .

grammar ：

UPDATE table_name　
SET column1 = value1, column2 = value2...., columnN = valueN
WHERE [condition];

notes ： These three lines are actually the same line .

Now I have the following data table ：

hold COMPANY In the table ID by 6 The customer address of is changed to Texas：

UPDATE COMPANY SET ADDRESS = 'Texas' WHERE ID = 6;

Modify the result ：

If you want to modify COMPANY In the table ADDRESS and SALARY All values for column , You don't need to use it WHERE Clause ,UPDATE Enquiries are as follows ：

UPDATE COMPANY SET ADDRESS = 'Texas', SALARY = 20000.00;

Modify the result ：

Two 、Ｃ/C++ operation

1. Interface API

The following interfaces can meet our basic needs , Need to learn more about operation , We can refer to the official documents .

Serial number

API & describe

sqlite3_open(const char *filename, sqlite3 **ppDb)

This routine opens a pointer to SQLite Connection to database files , Returns a for other SQLite The database connection object of the program .

If filename Parameter is NULL or ‘:memory:’, that sqlite3_open() Will be in RAM Create an in memory database , This will only happen session For the duration of .

If the filename filename Not for NULL, that sqlite3_open() This parameter value will be used to try to open the database file . If the file with that name does not exist ,sqlite3_open() A new database file with that name will be created and opened .

sqlite3_exec(sqlite3*, const char *sql, sqlite_callback, void *data, char **errmsg)

This routine provides an execution SQL Shortcut to command ,SQL The order was given by sql Parameters are provided , There can be more than one SQL Command composition .

ad locum , The first parameter sqlite3 Is an open database object ,sqlite_callback It's a callback ,data As its first parameter ,errmsg Will be returned to get any errors generated by the program .

sqlite3_exec() The program is parsed and executed by sql Every command given by the parameter , Until the end of the string or an error is encountered .

sqlite3_close(sqlite3*)

This routine calls... Before closing sqlite3_open() Open database connection . All connection related statements should be completed before the connection is closed .

If there are still queries that have not been completed ,sqlite3_close() Will return SQLITE_BUSY Disable closing error message .

2. Connect to database

Below C The code snippet shows how to connect to an existing database . If the database doesn't exist , Then it will be created , Finally, a database object will be returned .

#include <stdio.h>
#include <sqlite3.h>

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;

   rc = sqlite3_open("test.db", &db);

   if( rc ){
      fprintf(stderr, "Can't open database: %s
", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully
");
   }
   sqlite3_close(db);
}

Compile command

gcc lianjie.c -l sqlite3

Running results

The input terminal ls -l Command found more than one test.db file , Pictured ：

３． Create table

Ｃ Creating a language table is similar to creating a terminal , Only the command is given by sqlite3_exec() Functional sql Parameters of the incoming . The format is as follows ：

sql = "CREATE TABLE COMPANY("  
     "ID INT PRIMARY KEY     NOT NULL," 
     "NAME           TEXT    NOT NULL," 
     "AGE            INT     NOT NULL," 
     "ADDRESS        CHAR(50)," 
     "SALARY         REAL );";

Sample code ：

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h> 

static int callback(void *NotUsed, int argc, char **argv, char **azColName){
   int i;
   for(i=0; i<argc; i++){
      printf("%s = %s
", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("
");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int  rc;
   char *sql;

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s
", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stdout, "Opened database successfully
");
   }

   /* Create SQL statement */
   sql = "CREATE TABLE COMPANY("  
     "ID INT PRIMARY KEY     NOT NULL," 
     "NAME           TEXT    NOT NULL," 
     "AGE            INT     NOT NULL," 
     "ADDRESS        CHAR(50)," 
     "SALARY         REAL );";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
   if( rc != SQLITE_OK ){
   fprintf(stderr, "SQL error: %s
", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Table created successfully
");
   }
   sqlite3_close(db);
   return 0;
}

Output results ：

Again ls -l:

We can see ,test.db The file size is significantly larger .

4. insert data

Similar to creating a table ,sql The parameter is set to ：

  sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  
     "VALUES (1, 'Paul', 32, 'California', 20000.00 ); " 
     "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  
     "VALUES (2, 'Allen', 25, 'Texas', 15000.00 ); "     
     "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" 
     "VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );" 
     "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" 
     "VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );";

Sample code ：

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h>

static int callback(void *NotUsed, int argc, char **argv, char **azColName){
   int i;
   for(i=0; i<argc; i++){
      printf("%s = %s
", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("
");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s
", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully
");
   }

   /* Create SQL statement */
   sql = "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  
     "VALUES (1, 'Paul', 32, 'California', 20000.00 ); " 
     "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY) "  
     "VALUES (2, 'Allen', 25, 'Texas', 15000.00 ); "     
     "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" 
     "VALUES (3, 'Teddy', 23, 'Norway', 20000.00 );" 
     "INSERT INTO COMPANY (ID,NAME,AGE,ADDRESS,SALARY)" 
     "VALUES (4, 'Mark', 25, 'Rich-Mond ', 65000.00 );";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s
", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Records created successfully
");
   }
   sqlite3_close(db);
   return 0;
}

Output results ：

５． Look up the table

sqlite3_exec() Provides us with a callback function , The statement is as follows ：

typedef int (*sqlite3_callback)(
void*,    /* Data provided in the 4th argument of sqlite3_exec() */
int,      /* The number of columns in row */
char**,   /* An array of strings representing fields in the row */
char**    /* An array of strings representing column names */
);

The first parameter ： That is, the data passed in by the fourth parameter

The second parameter ： The number of columns in a row

The third parameter ： An array of strings representing fields in a row , That is, the data in each row

Fourth parameter ： An array of strings representing column names , Set when creating the linked list

Execute the process ： Look up the table , Whether there is any qualified data . Yes , perform sqlite3_callback() function ; No, , sign out

That's it , Let's take an example ：

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h>

static int callback(void *data, int argc, char **argv, char **azColName){
   int i;
   fprintf(stderr, "%s: ", (const char*)data);
   for(i=0; i<argc; i++){
      printf("%s = %s
", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("
");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;
   const char* data = "Callback function called";

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s
", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully
");
   }

   /* Create SQL statement */
   sql = "SELECT * from COMPANY";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, (void*)data, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s
", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Operation done successfully
");
   }
   sqlite3_close(db);
   return 0;
}

The above program shows how to create from the previous COMPANY Get and display records in the table , The output is as follows ：

I do not specify the query conditions here , Means to query all .

６． Data deletion

sql Parameter setting ：

sql = "DELETE from COMPANY where ID=2; " \ Delete ＩＤ be equal to ２ The line of 
         "SELECT * from COMPANY";        \ Display table

The difference between this and the above is that there is one more command , The surface of the sql Parameters can consist of multiple commands .

Sample code ：

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h> 

static int callback(void *data, int argc, char **argv, char **azColName){
   int i;
   fprintf(stderr, "%s: ", (const char*)data);
   for(i=0; i<argc; i++){
      printf("%s = %s
", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("
");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;
   const char* data = "Callback function called";

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s
", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully
");
   }

   /* Create merged SQL statement */
   sql = "DELETE from COMPANY where ID=2; " 
     "SELECT * from COMPANY";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, (void*)data, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s
", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Operation done successfully
");
   }
   sqlite3_close(db);
   return 0;
}

Output ：

７．UPDATE operation

The operation sample ：

#include <stdio.h>
#include <stdlib.h>
#include <sqlite3.h> 

static int callback(void *data, int argc, char **argv, char **azColName){
   int i;
   fprintf(stderr, "%s: ", (const char*)data);
   for(i=0; i<argc; i++){
      printf("%s = %s
", azColName[i], argv[i] ? argv[i] : "NULL");
   }
   printf("
");
   return 0;
}

int main(int argc, char* argv[])
{
   sqlite3 *db;
   char *zErrMsg = 0;
   int rc;
   char *sql;
   const char* data = "Callback function called";

   /* Open database */
   rc = sqlite3_open("test.db", &db);
   if( rc ){
      fprintf(stderr, "Can't open database: %s
", sqlite3_errmsg(db));
      exit(0);
   }else{
      fprintf(stderr, "Opened database successfully
");
   }

   /* Create merged SQL statement */
   sql = "UPDATE COMPANY set SALARY = 25000.00 where ID=1; " 
     "SELECT * from COMPANY";

   /* Execute SQL statement */
   rc = sqlite3_exec(db, sql, callback, (void*)data, &zErrMsg);
   if( rc != SQLITE_OK ){
      fprintf(stderr, "SQL error: %s
", zErrMsg);
      sqlite3_free(zErrMsg);
   }else{
      fprintf(stdout, "Operation done successfully
");
   }
   sqlite3_close(db);
   return 0;
}

Output results ：