sqlite3学习

基本API和过程：

参考： http://www.blogjava.net/xylz/archive/2012/09/25/388519.html\
官网：http://www.sqlite.org/cintro.html
http://www.cnblogs.com/stephen-liu74/archive/2012/03/05/2340780.html http://www.cnblogs.com/nbsofer/archive/2012/05/02/2479168.html http://www.cnblogs.com/memset/archive/2012/05/02/2479156.html
例子程序：

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

int main()
{
int ret;
sqlite3* pDb = NULL;
char* pErrMsg = NULL;
printf("Open db\n");
ret = sqlite3_open("./my.db", &pDb);//Open the db file
assert(SQLITE_OK == ret);

printf("Clear data\n");
sqlite3_exec(pDb, "drop table if exists myTable\n", NULL, NULL, NULL);

printf("Create table\n");
ret = sqlite3_exec(pDb, "create table if not exists myTable(id integer primary key, name text)", NULL, NULL, &pErrMsg);//Create a table
if (SQLITE_OK != ret) printf("%s\n", pErrMsg);
assert(SQLITE_OK == ret);
sqlite3_free(pErrMsg);//TODO:ÊÇ·ñҪÿ´Îsqlite3_exec¶¼free¶ø²»ÊÇÖ»freeÒ»´Î?

printf("Insert some lines\n");
ret = sqlite3_exec(pDb, "insert into myTable(id,name) values(2,'2222222')", NULL, NULL, &pErrMsg);
ret = sqlite3_exec(pDb, "insert into myTable(id,name) values(3,'3333333')", NULL, NULL, &pErrMsg);
ret = sqlite3_exec(pDb, "insert into myTable(id,name) values(11,'11111')", NULL, NULL, &pErrMsg);
//if (SQLITE_OK != ret) printf("%s\n", pErrMsg);
assert(SQLITE_OK == ret);

printf("Insert a line that contained ' \n");
char* sql = sqlite3_mprintf("insert into myTable(id,name) values(14,'%q')", "luo'jiao");
printf("sql: %s\n", sql);
ret = sqlite3_exec(pDb, sql, NULL, NULL, NULL);
assert(SQLITE_OK == ret);
sqlite3_free(sql);

printf("Delete some lines\n");
//ret = sqlite3_exec(pDb, "delete from myTable where id < 10", NULL, NULL, &pErrMsg);

printf("Use prepare&step to insert a line\n");
sqlite3_stmt *stmt;
ret = sqlite3_prepare_v2(pDb, "insert into myTable(id,name) values(?,?)", -1, &stmt, NULL);
assert(SQLITE_OK == ret);
for (int i = 30; i < 33; i++)
{
sqlite3_bind_int(stmt, 1, i);
char text[50] = {0};
sprintf(text, "prepare line id%d", i);
sqlite3_bind_text(stmt, 2, text, -1, NULL);
sqlite3_step(stmt);
sqlite3_reset(stmt);
}
sqlite3_finalize(stmt);
assert(SQLITE_OK == ret);

printf("Select some data from table, result:\n");
sqlite3_stmt *stmt1;
const char* sql1 = "select * from myTable where id > 10";
printf("Sql: select * from myTable where id > 10\nid  name\n");
ret = sqlite3_prepare_v2(pDb, sql1, -1, &stmt1, NULL);
assert(SQLITE_OK == ret);
while (SQLITE_ROW == sqlite3_step(stmt1))
{
int id = sqlite3_column_int(stmt1, 0);
const unsigned char* pName = sqlite3_column_text(stmt1, 1);
printf("%-4d%s\n", id, pName);
}
ret = sqlite3_finalize(stmt1);
assert(SQLITE_OK == ret);

sqlite3_close(pDb);
return 0;
}

基本SQL语句

更新：UPDATE myTable
SET address = 'Nanjing', name = 'luojiao'WHEREid = 1;

复合插入：

INSERT OR REPLACE：如果不存在就插入，存在就更新

INSERT OR IGNORE：如果不存在就插入，存在就忽略

模糊匹配：用like替代等号并使用通配符%，例如： select * from mytable where id like '1111%'; select * from mytable where name like 'line%';

like 使用%代表任何字符

like 使用?代表单个字符

matches使用*代表任何字符

matches使用_代表单个字符

例如：

select * from t_test where name matches "*"

根据表创建新表

举例：

CREATE TABLE newTable
AS SELECT id, name FROM existedTable WHERE id < 10;

触发器（Trigger）：

参考http://blog.csdn.net/dliyuedong/article/details/40565407

CREATE TRIGGER < [ BEFORE | AFTER ] > < [ INSERT | UPDATE | DELETE ] >

ON <tableName>

FOR EACH ROW //可选，不写也一样

BEGIN

--do something; //记得句末一定要加分号

END ;

例如：

CREATE TRIGGER myTrigger1 after delete on myTable

BEGIN

delete from relatedTable where relatedTable.id = old.id;

END;

其中前面作用表的新旧数据使用new和old进行指向，例如insert时new指向插入的行数据，delete时old指向删除的行数据，update时类推。

注意：sqlite3的触发器语法跟SqlServer等大型数据库不太一样，参照SqlServer的方式来写会无法执行，例如不需要关键字as，也不能用关键字for（只能用before/after），一定要有begin/end，一定要do something语句后加分号

虚拟表virtual table

参考官网：http://www.sqlite.org/vtab.html

create/drop table时，调用xCreate/xConnect和xDestroy/xDisconnect，在这四个函数里实现表的创建销毁。

select时，xBestIndex、xOpen、xFilter、xEof、xColumn、xRowid、xNext、xClose配合使用，调用顺序就是我列的顺序。

xBestIndex 用来处理SQL语句中的WHERE/GROUP BY/ORDER BY这样的约束条件的。入参是sqlite3_index_info中的 /* Inputs */ 部分，出参是sqlite3_index_info中的 /* Outputs */ 部分。每一个WHERE约束条件对应一个aConstraint结构，每一个ORDER BY等对应一个aOrderBy结构。

解析完成后，如果希望哪个约束条件aConstraint[i]被传递到XFilter的argv
，那就填写aConstraintUsage[i].argvIndex = n;

idxNum和idxStr的含义自己定义，会传给xFilter，含义由使用者自定，比较灵活

XFilter 用来进行行选择，根据xBestIndex传过来的条件，选出符合条件的行。

例子代码： 每次执行前要把my.db或里面的virTable表删除，否则会创建失败。加了if not exists会失败。

#include <stdio.h>
#include <assert.h>
#include <string.h>
#include <sqlite3.h>
//#include <sqlite3ext.h>

/************************* VT的数据库表信息 *************************/
/*这里建一个最简单的数据库table:
vtable(id int, name text)
1,      aaa
2,      bbb
3,      ccc
4,      ddd
5,      eee
*/
const int DATA_COUNT = 5;//table大小即行数
static int gIDinTable[DATA_COUNT] = {1,2,3,4,5};//table中的id列数据
const int NAME_LENGTH = 10;
static char gNameinTable[DATA_COUNT][NAME_LENGTH] = {"aaa","bbb","ccc","ddd","eee"};//table中的name列数据
static int curPos = 0;//当前cursor
/************************* VT的数据库表信息 *************************/

static int MyDestructor(sqlite3_vtab *pVtab) // finished: 100%
{
printf("MyDestructor\n");
return SQLITE_OK;
}

static int MyCreate( sqlite3 *db, void *p_aux, int argc, const char * const* argv , sqlite3_vtab **pp_vt,   char **pzErr ) // finished: 100%
{
printf("MyCreate\n");
int ret = sqlite3_declare_vtab(db, "create table vtable(id int, name text)");
if (SQLITE_OK != ret)
{
return SQLITE_ERROR;
}
sqlite3_vtab* pVtab = (sqlite3_vtab*)sqlite3_malloc(sizeof(sqlite3_vtab));
*pp_vt = (sqlite3_vtab *)pVtab;
return SQLITE_OK;
}

static int MyConnect( sqlite3 *db, void *p_aux, int argc, const char * const *argv, sqlite3_vtab **pp_vt, char **pzErr ) // finished: 100%
{
printf("MyConnect\n");
return MyCreate(db, p_aux, argc, argv, pp_vt, pzErr);
return SQLITE_OK;
}

static int MyBestIndex(sqlite3_vtab *tab, sqlite3_index_info *pIdxInfo) // finished: 100%
{
printf("MyBestIndex\n");
//TODO: 这里的aConstraintUsage是谁申请的内存? 应该是只有select语句有条件约束这个就自动申请了?需要看下
//pIdxInfo->aConstraintUsage[0].argvIndex = 1;
return SQLITE_OK;
}

static int MyDisconnect(sqlite3_vtab *pVtab) // finished: 100%
{
printf("MyDisconnect\n");
sqlite3_free(pVtab);
return SQLITE_OK;
}

static int MyDestroy(sqlite3_vtab *pVtab) // finished: 100%
{
printf("MyDestroy\n");

return MyDisconnect(pVtab);;
}

static int MyOpen(sqlite3_vtab *pVTab, sqlite3_vtab_cursor **pp_cursor) // finished: 100%
{
printf("MyOpen\n");
sqlite3_vtab_cursor* pCursor = (sqlite3_vtab_cursor*)sqlite3_malloc(sizeof(sqlite3_vtab_cursor));
if (pCursor == NULL)
{
return SQLITE_NOMEM;
}
*pp_cursor = pCursor;
//严格来说，这里应该扩展sqlite3_vtab_cursor来包含curPos，作为cursor的记录。例子就从简了,用全局变量
curPos = 0;//Open时把cursor初始化

return SQLITE_OK;
}

static int MyClose(sqlite3_vtab_cursor *cur) // finished: 100%
{
printf("MyClose\n");
if (cur)
{
sqlite3_free(cur);
}
return SQLITE_OK;
}

static int MyFilter( sqlite3_vtab_cursor *p_vtc, int idxNum, const char *idxStr, int argc, sqlite3_value **argv ) // finished: 80%
{
printf("MyFilter\n");
//根据条件来筛选出符合条件的行
return SQLITE_OK;
}

static int MyNext(sqlite3_vtab_cursor *cur) // finished: 100%
{
printf("MyNext\n");
curPos++;//Next时把cursor递增。严格说应该是cur结构体中带过来筛选条件，在这里根据筛选条件找Next，但例子就从简了
return SQLITE_OK;
}

static int MyEof(sqlite3_vtab_cursor *cur) // finished: 100%
{
printf("MyEof\n");
//严格说应该是判断，符合cur结构体中带过来筛选条件的行是否结束，但例子就从简了
if (curPos >= DATA_COUNT)
{
return 1;
}
else
{//0 ~ DATA_COUNT-1
return 0;
}
}

static int MyColumn(sqlite3_vtab_cursor *cur, sqlite3_context *ctx, int column) // finished: 80%
{
printf("MyColumn\n");
switch (column)

{
case 0://id
sqlite3_result_int(ctx, gIDinTable[curPos]);
break;
case 1://name
sqlite3_result_text(ctx, gNameinTable[curPos], strlen(gNameinTable[curPos]), SQLITE_STATIC);
break;
default:
break;
}
return SQLITE_OK;
}

static int MyRowid(sqlite3_vtab_cursor *cur, sqlite_int64 *p_rowid) // finished: 100%
{
printf("MyRowid\n");
*p_rowid = (sqlite_int64)curPos;
return SQLITE_OK;
}

static int MyUpdate(sqlite3_vtab *pVTab,int argc,sqlite3_value **argv,sqlite_int64 *pRowid)
{
printf("MyUpdate\n");
return SQLITE_OK;
}

static int MyFindFunction( sqlite3_vtab *pVtab, int nArg,const char *zName,
void (**pxFunc)(sqlite3_context*,int,sqlite3_value**),
void **ppArg )
{
printf("MyFindFunction\n");
return SQLITE_OK;
}

static sqlite3_module myModule =
{
1, /* iVersion */
MyCreate, /* xCreate - create a vtable */
MyConnect, /* xConnect - associate a vtable with a connection */
MyBestIndex, /* xBestIndex - best index */
MyDisconnect, /* xDisconnect - disassociate a vtable with a connection */
MyDestroy, /* xDestroy - destroy a vtable */
MyOpen, /* xOpen - open a cursor */
MyClose, /* xClose - close a cursor */
MyFilter, /* xFilter - configure scan constraints */
MyNext, /* xNext - advance a cursor */
MyEof, /* xEof - inidicate end of result set*/
MyColumn, /* xColumn - read data */
MyRowid, /* xRowid - read data */
MyUpdate, /* xUpdate - write data */
NULL, /* xBegin - begin transaction */
NULL, /* xSync - sync transaction */
NULL, /* xCommit - commit transaction */
NULL, /* xRollback - rollback transaction */
MyFindFunction, /*  xFindFunction - function overloading */
NULL,
NULL,
NULL,
NULL
};

int main()
{
int ret;
sqlite3* pDb = NULL;
printf("Open db\n");
ret = sqlite3_open("./my.db", &pDb);//Open the db file
assert(SQLITE_OK == ret);

//Create virtual table
ret = sqlite3_create_module(pDb, "MyVT", &myModule, NULL);
assert(SQLITE_OK == ret);
printf("Create virtual table\n");
ret = sqlite3_exec(pDb, "create virtual table virTable using MyVT", NULL, NULL, NULL);//Create a table
assert(SQLITE_OK == ret);

//Execute a select clause
ret = sqlite3_exec(pDb, "select * from virTable", NULL, NULL, NULL);//Create a table
assert(SQLITE_OK == ret);

//Execute a select clause and get result
sqlite3_stmt *stmt;
ret = sqlite3_prepare_v2(pDb, "select * from virTable", -1, &stmt, NULL);
printf("id  name\n");
while (SQLITE_ROW == sqlite3_step(stmt))
{
int id = sqlite3_column_int(stmt, 0);
const unsigned char* pName = sqlite3_column_text(stmt, 1);//pName会被sqlite3自动释放，不用外界释放
printf("%-4d %s\n", id, pName);
}
sqlite3_finalize(stmt);
assert(SQLITE_OK == ret);

sqlite3_close(pDb);
return 0;
}

rowid

SQL默认有一个rowid列，int64格式，这个列是自动生成的，一般是递增的，不用去指定。可以select语句把它显示出来。

效率提升

BEGIN TRANSACTION - COMMIT ：对于Insert和Update这样的有IO的操作，如果每个语句都单独执行，大量操作时就会有大量的IO操作，会非常慢。例如Insert 10000条数据会耗费十几秒的时间。

加速方法： 在批量语句前加 BEGIN TRANSACTION, 之后加 COMMIT, 这样所有的IO操作会被缓存，到COMMIT时统一执行只进行一次IO操作。效果非常明显，几百倍的速度提升。

还有一个"PRAGMA synchronous = OFF"语句，但测试过不起作用，速度没加快。