Embedded database development programming (zero)

One database

1.1 stay ubuntu Install database in

sudo apt-get install sqlite3 libsqlite3-dev
Install the test ：
Input sqlite3, If you can successfully access the database , Description installation successful ：

1.2 Operation of database

1.2.1 Classification of database commands

System commands ： In order to . The first order , It is mainly used to operate the current database
Be careful ： The system command cannot be followed by ;
A common order ： In order to ; The order at the end , It mainly operates the tables in the database
Be careful ： Ordinary commands cannot be preceded by .

1.2.2 Common system commands

.help： View help information , List all system commands
.exit: Exit database
.quit： Exit database
.databases: View the current database information
.tables: List the table names of all tables in the current database
.schema: List the structure of all tables in the database

1.2.3 Common statements in data

--  Get into sqlite3
sqlite3 student.db
--  Exit database 
.exit

--  Create a table 
 create table stu(id int,name char,sex char,score int);
  Be careful ： The type of character or string is specified as char perhaps text
 
 --  View table structure 
 .schema
 --  insert data 
 insert into stu (id,name,sex,score) values(1001,"zhangsan",'m',98);
 insert into stu values(1002,"lisi",'f',99);
 insert into stu values(1003,"wanger",'m',100),(1004,"xiaoming",'f',101);
 
 -- Query data 
select * from stu;  // Find all records 
select *from stu where sex='f'; // Find records that match the criteria 
select *from stu where sex='f' and id = 1002; 
select *from stu where sex='f' or id = 1001;
select id,name from stu;  // Query only id and name

--  Delete record 
delete from stu where id = 1001;
--  Modify the record 
update stu set score=77 where id = 1003;

-- Add a column 
alter table stu add column vip int;

-- Delete a column 
    sqlites It is not allowed to delete a column directly 
    1） First create a new table 
    create table stu1 as select id,name from stu;
    2)  Delete the old table 
    drop table stu;
    3) Rename the new table 
    alter table stu1 rename to stu;
--  Database primary key （ The set data will be unique ）
    create table usr(name text primary key,passwd text);
--  Delete table 
    drop table stu;

1.3 sqlite Commonly used in database api

1.3.1 sqlite3_open

The header file :#include <sqlite3.h>
Prototype ：int sqlite3_open(const char *filename,sqlite3 **ppDb);
function ： Open or create a database
Parameters ：
filename: Database name
PPdb: Pointer to the operation database , Handle .
Return value ：
success ： return ：SQLITE_OK
Failure ：error_code It can be done by sqlite3_errmsg Get error messages

1.3.2 int sqlite3_close(sqlite3 * db)

function : Shut down a database

1.3.3 sqlite3_exec

The header file :#include <sqlite3.h>
Prototype ：int sqlite3_exec(sqlite3 db,const char sql,int (callback)(void ,int,char,char),void *arg,char errmsg);
function ： To perform a sql sentence
Parameters ：
db： Handle pointer to the database
sql: Will be executed sql sentence
callback: Callback function , Only when querying statements , Will pass parameters to the callback function
arg: by callback Ginseng
errmsg: Error message address
Return value ：
success ： return ：SQLITE_OK
Failure ：error_code It can be done by sqlite3_errmsg Get error messages
******************************************************
int (*callback)(void *arg,int ncolumn,charf_value,char**f_name)
function ： Get the results of the query
Parameters ：
arg: Used for parameter passing of callback function
ncolumn: The number of fields the record contains （ Number of columns ）
f_value: An array of pointers containing the values of each field
f_name： An array of pointers containing the names of each field
Return value ：
success 0
error ： Not 0

1.3.4 sqlite3_get_table

Prototype ：int sqlite3_get_table(sqlite3 *db,const char *sql,char ***pazresult,int *pnRow,int *pnColumn,char **pzErrmsg);
function ： Query the database , It creates a new memory area to store the result information of the query
Parameters ：
db： Handle pointer to the database
sql: Will be executed sql sentence
pazresult： Result of query
pnRow： Row number
pnColumn Number of columns
pzErrmsg error message
Return value ：
success 0
error ：errcode
pnRow The value of is the number of qualified records （ Field name is not included ）.
pnColumn The value of is the number of qualified fields .

1.3.5 void sqlite3_free_table(char ** result)

function ： Free memory

#include <stdio.h>
#include <sqlite3.h>
#include <string.h>
int print(void *arg,int column,char **value,char **name)  //column Is the number of columns ,name: Field name  value: data 
{
    
    int i;
    for(i = 0 ; i < column;i++)
    {
    
        printf("%s = %s ",name[i],value[i]);
    }
    printf("\n");
    return 0;
}
int main(int argc, char const *argv[])
{
    
    sqlite3 *ppdb;
    // Open or create a database 
    int ret = sqlite3_open("stu.db",&ppdb);
    if(ret != SQLITE_OK)
    {
    
        printf("sqlite3 open: %s\n",sqlite3_errmsg(ppdb));
        return -1;
    }
    // Create table 
    char sql[128] = {
    0};
    sprintf(sql,"create table if not exists stu(id int,name char,sex char,score int);");
    ret = sqlite3_exec(ppdb,sql,NULL,NULL,NULL);
    if(ret != SQLITE_OK)
    {
    
        printf("sqlite3_exec: %s\n",sqlite3_errmsg(ppdb));
        return -1;        
    }
    // insert data 
    int i;
    int id,score;
    char name[32] = {
    0};
    char sex;
    /*for(i = 0; i < 2;i++) { printf(" Please enter the student number 、 full name 、 Gender 、 fraction ：\n"); scanf("%d%s %c %d",&id,name,&sex,&score); memset(sql,0,sizeof(sql)); sprintf(sql,"insert into stu values(%d,'%s','%c',%d);",id,name,sex,score); ret = sqlite3_exec(ppdb,sql,NULL,NULL,NULL); if(ret != SQLITE_OK) { printf("sqlite3_exec2: %s\n",sqlite3_errmsg(ppdb)); return -1; } }*/
    memset(sql,0,sizeof(sql));
    sprintf(sql,"select * from stu;");
    /*ret = sqlite3_exec(ppdb,sql,print,NULL,NULL); if(ret != SQLITE_OK) { printf("sqlite3_exec: %s\n",sqlite3_errmsg(ppdb)); return -1; }*/
    char **result;
    int row,column;
    ret = sqlite3_get_table(ppdb,sql,&result,&row,&column,NULL);  //row: That's ok  column: Column 
    if(ret != SQLITE_OK)
    {
    
        printf("sqlite3_get_table : %s\n",sqlite3_errmsg(ppdb));
        return -1;
    }
    int j;
    int Index = column;
    for(i = 0; i < row;i++)   // That's ok 
    {
    
        for(j = 0; j < column;j++)   // Column 
        {
    
            printf("%s = %s ",result[j],result[Index]);
            Index++;
        }
        putchar(10);
    }
    return 0;
}