如何在SQLite中找到一个数字的权力 [英] How to find power of a number in SQLite

问题描述

我想更新我的数据库中的兴趣字段SQL查询如下所示

I want to update Interest field in my database SQL query is like as per below

更新Table_Name set Interest = Principal * Power （1 +（rate /
100），year）

Update Table_Name set Interest = Principal * Power(( 1 + (rate / 100),year)

此查询在MYSQL中正常工作， in SQLite for objetive c

This query is work fine in MYSQL but don't work in SQLite for objetive c

错误说没有电源功能

有没有人知道如何解决这个问题，因为我使用查询，因为我需要更新更多的3000条记录的时间。

Did anyone knows how to resolve this problem as I have do this using query because I need to update more thans 3000 record at time.

感谢提前

推荐答案

sqlite没有很多功能，但好消息是很容易添加自己的。

sqlite doesn't have a lot of functions available. But the good news is that is easy enough to add your own.

首先写一个幂函数：

void sqlite_power(sqlite3_context *context, int argc, sqlite3_value **argv) {
    double num = sqlite3_value_double(argv[0]); // get the first arg to the function
    double exp = sqlite3_value_double(argv[1]); // get the second arg
    double res = pow(num, exp);                 // calculate the result
    sqlite3_result_double(context, res);        // save the result
}

然后您需要注册函数：

    int res = sqlite3_create_function(dbRef, "POWER", 2, SQLITE_UTF8, NULL, &sqlite_power, NULL, NULL);

2 功能。 dbRef 当然是 sqlite3 * 数据库引用。

The 2 is the number of arguments for the function. dbRef is of course the sqlite3 * database reference.

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