如何检查sqlite中是否存在记录C
我刚从sqlite开始,需要一些快速帮助。我有以下代码正在工作。在最后一个查询中,例如"Select * from company where id = 2"
。我只想检查是否存在一排有id = 2
。而已。但我无法做到这一点。回调方法对于所有查询都很常见,因此无法对其进行修改,也不希望为上次查询编写特定回调。如何检查sqlite中是否存在记录C
对于最后一个查询,我可以只获得0/1
或False/True
吗? 我试过的是,使用,计数行,但再次回调它打印结果,但不是0/1。
static int callback(void *NotUsed, int argc, char **argv, char **azColName){
int i;
for(i=0; i<argc; i++){
printf("%s = %s\n", azColName[i], argv[i] ? argv[i] : "NULL");
}
printf("\n");
return 0;
}
int main()
{
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\n", sqlite3_errmsg(db));
exit(0);
}else{
fprintf(stderr, "Opened database successfully\n");
}
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\n", zErrMsg);
sqlite3_free(zErrMsg);
}else{
fprintf(stdout, "Table created successfully\n");
}
/* 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\n", zErrMsg);
sqlite3_free(zErrMsg);
}else{
fprintf(stdout, "Records created successfully\n");
}
sql = "Select * from COMPANY where id = 2";
rc = sqlite3_exec(db, sql, callback, 0, &zErrMsg);
if(rc != SQLITE_OK){
fprintf(stderr, "SQL error: %s\n", zErrMsg);
sqlite3_free(zErrMsg);
}else{
fprintf(stdout, "Records created successfully\n");
}
sqlite3_close(db);
return 0;
}
你可以Exec的查询不同
sql = "Select * from COMPANY where id = 2";
struct sqlite3_stmt *selectstmt;
int result = sqlite3_prepare_v2(db, sql, -1, &selectstmt, NULL);
if(result == SQLITE_OK)
{
if (sqlite3_step(selectstmt) == SQLITE_ROW)
{
// record found
}
else
{
// no record found
}
}
sqlite3_finalize(selectstmt);
我越来越核心愚蠢的__pthread_mutex_lock错误:断言'互斥 - > __数据.__所有者== 0'失败。我们可以使用其他类似SELECT EXISTS的东西吗? – impossible
不确定我得到你:看看[在这个手册页](http://www.techonthenet.com/sqlite/exists.php) – LPs
我改变了你的答案,现在它为我工作。请接受编辑。我接受了答案。感谢您的回答。 – impossible
为什么不能你写这一个单独的回调函数? –
但我希望tor在rc中返回1或0,表示是否存在行。或者我如何获得回调函数的返回值? – impossible
回调函数的返回值指示是否发生错误,就像'sqlite3_exec'的返回值一样。 –