【iOS开发-104】SQLite使用：注意查询时分步写while会出现死循环

概述（1）注意点： 在SELECT查询时，不能分步写成如下形式，否则会出现死循环： int stepResult=sqlite3_step(statement);while (stepResult==SQLITE_ROW) {}只能合并成一句写成： while (sqlite3_step(statement)==SQLITE_ROW) { } 因为，sqlite3_step的

（1）注意点：

在SELECT查询时，不能分步写成如下形式，否则会出现死循环：

int stepResult=sqlite3_step(statement);while (stepResult==sqlITE_ROW) {}

只能合并成一句写成：

while (sqlite3_step(statement)==sqlITE_ROW) {         }

因为，sqlite3_step的执行方式是如下：

** ^If the sql statement being executed returns any data,then [sqlITE_ROW]

** is returned each time a new row of data is ready for processing by the

** caller. The values may be accessed using the [column access functions].

** sqlite3_step() is called again to retrIEve the next row of data.

#import "VIEwController.h"#import <sqlite3.h>@interface VIEwController ()- (IBAction)insert:(ID)sender;- (IBAction)delete:(ID)sender;- (IBAction)update:(ID)sender;- (IBAction)select:(ID)sender;@end@implementation VIEwControllerstatic sqlite3 *_db;- (voID)vIEwDIDLoad {    [self setupDatabaseAndtable];    [super vIEwDIDLoad];    // Do any additional setup after loading the vIEw,typically from a nib.}- (voID)dIDReceiveMemoryWarning {    [super dIDReceiveMemoryWarning];    // dispose of any resources that can be recreated.}-(voID)setupDatabaseAndtable{    Nsstring *filename=[[NSSearchPathForDirectorIEsInDomains(NSdocumentDirectory,NSUserDomainMask,YES) lastObject] stringByAppendingPathComponent:@"iOS.sql"];    NSLog(@"%@",filename);        int openDBResult=sqlite3_open(filename.UTF8String,&_db);        if (openDBResult==sqlITE_OK) {        //创建表        Nsstring *createtablesql=@"CREATE table IF NOT EXISTS user (ID INTEGER PRIMARY KEY autoINCREMENT,name TEXT,age INTEGER);";        char *error=nil;        int createtableResult=sqlite3_exec(_db,createtablesql.UTF8String,NulL,&error);        if (createtableResult==sqlITE_OK) {            NSLog(@"创建表成功");        }else{            NSLog(@"创建表失败");        }        NSLog(@"打开数据库成功");    }else{        NSLog(@"打开数据库失败");    }}- (IBAction)insert:(ID)sender {    for (int i=0; i<50; i++) {        Nsstring *name=[Nsstring stringWithFormat:@"jack%d",arc4random()%100];        int age=arc4random()%100;        Nsstring *inserttablesql=[Nsstring stringWithFormat:@"INSERT INTO user(name,age) VALUES('%@',%d);",name,age];        char *error=nil;        int insertResult=sqlite3_exec(_db,inserttablesql.UTF8String,&error);        if (insertResult==sqlITE_OK) {            NSLog(@"%d %@ %d",i,age);        }else{            NSLog(@"插入数据失败");        }    }}- (IBAction)delete:(ID)sender {    Nsstring *deleteRowsql=@"DELETE FROM user WHERE ID=1;";    char *error=nil;    int deleteResult=sqlite3_exec(_db,deleteRowsql.UTF8String,&error);    if (deleteResult==sqlITE_OK) {        NSLog(@"删除数据成功");    }else{        NSLog(@"删除数据失败");    }}- (IBAction)update:(ID)sender {    Nsstring *updateRowsql=@"UPDATE user SET age=130 WHERE ID=3;";    char *error=nil;    int updateResult=sqlite3_exec(_db,updateRowsql.UTF8String,&error);    if (updateResult==sqlITE_OK) {        NSLog(@"修改数据库成功");    }else{        NSLog(@"修改数据库失败");    }}- (IBAction)select:(ID)sender {    Nsstring *selectRowsql=@"SELECT ID,age FROM user WHERE ID=5;";    sqlite3_stmt *statement;    int stmtResult=sqlite3_prepare_v2(_db,selectRowsql.UTF8String,-1,&statement,nil);    if (stmtResult==sqlITE_OK) {        NSLog(@"stmtResult成功");        //以下语句分步写会出现死循环        while (sqlite3_step(statement)==sqlITE_ROW) {            NSLog(@"stepResult成功");            int uID=sqlite3_column_int(statement,0);            const unsigned char *uname=sqlite3_column_text(statement,1);            int uage=sqlite3_column_int(statement,2);            NSLog(@"%d %s %d",uID,uname,uage);        }    }else{        NSLog(@"stmtResult失败");    }}@end

（2）防止sql注入的简单处理，利用sqlite3_bind_text(int)等进行变量绑定，这个语句会对输入的字符进行处理。

- (IBAction)select:(ID)sender {    Nsstring *selectRowsql=@"SELECT ID,age FROM user WHERE name=?;";    sqlite3_stmt *statement;    int stmtResult=sqlite3_prepare_v2(_db,nil);    if (stmtResult==sqlITE_OK) {        NSLog(@"stmtResult成功");        sqlite3_bind_text(statement,1,"jack1",NulL);        //以下语句分步写会出现死循环        while (sqlite3_step(statement)==sqlITE_ROW) {            NSLog(@"stepResult成功");            int uID=sqlite3_column_int(statement,uage);        }    }else{        NSLog(@"stmtResult失败");    }}

（3）liKE模糊查询关键词的使用，需要注意的是查询的词的两边需要各增加一个%，而如果用变量替换用转义的话，需要使用%%表示%，所以一般格式是“%%关键字%%”。

- (IBAction)select:(ID)sender {    Nsstring *selectRowsql=@"SELECT ID,age FROM user WHERE name liKE ?;";    sqlite3_stmt *statement;    int stmtResult=sqlite3_prepare_v2(_db,"%%jack1%%",uage);        }    }else{        NSLog(@"stmtResult失败");    }}

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