如何查看和操作真机运行的数据库

查看当前设备，下载当前app的container，然后查看其包内容，按照数据库的存储位置，可以找到对应的sqlite文件，然后用Navicat 链接该数据库文件即可查看。
https://blog.csdn.net/wuzesong/article/details/51324324

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如何查找前5条数据

网络上找到的 select top 5 * from table_name 是不起作用的，报语法错误，因为这是SQL的语法。
在MySQL、Sqlite中的语法是：select * from table_name limit 0,5

https://www.cnblogs.com/xkms/p/4664473.html

按照时间排序，只保留前5条数据，其他的都删除

delete from table_name where id not in (select id from table_name where uid = 666 order by timestamp desc limit 0,5)

FMDB中的增删改查

// 删除数据
NSString *deleteSQL = [NSString stringWithFormat:@"DELETE FROM %@ WHERE uid = %@ and targetid = %@", tableName, uid, targetid];
[db executeUpdate:deleteSQL];
        
// 插入数据
NSString *insertSQL = [NSString stringWithFormat:@"INSERT INTO %@ ('uid','targetid','timestamp') VALUES (?,?,?)", tableName];
[db executeUpdate:insertSQL, uid, targetid, timestamp];

// 更新数据
NSString *updateSQL = [NSString stringWithFormat:@"UPDATE %@ SET timestamp=?, content=? WHERE uid=%@ and targetid=%@", tableName, uid, targetid];
[db executeUpdate:updateSQL, timestamp, content];

// 查看数据（按时间降序排序）
NSString *sql = [NSString stringWithFormat:@"SELECT * FROM %@ where uid = %ld ORDER BY timestamp DESC", tableName, uid];
FMResultSet *rs = [db executeQuery:sql];
while ([rs next]) {
     [rs objectForColumn:@"targetid"];
     [rs objectForColumn:@"timestamp"];
}