sqlite3的故事

主要还是在数据库内容同步的时候遇到的问题，服务器端也不标识变化发生，那客户端用sqilite3,本来就是要实现目的，udpate不成功，我就用insert。

自然想到去拿那个影响的record数目。

但看来大家多推荐replace，这个replace是不是要知道原来sql的primarykey的值啊，可我偷懒，没设置，全用了一个自增长的id，这下。。。

因为数据库建表时没有指定primary key, 所以replace语句不正常.  

option 1 would look like:  ／／基本来说，目前的数据结构，表，应该可以做到用replace or insert。。。。。

NSString * update = [NSString stringWithFormat:@"INSERT OR REPLACE INTO LIST (COUNT, NAME, DATE, IDNUM) VALUES (?, ?, ?, ?)"];

option 2 would look like:  ／／至于效率问题，我们需要找个同学测试下。。。。

NSString * update = [NSString stringWithFormat:@"SELECT * FROM LIST WHERE IDNUM = '%i'", [accessID integerValue]];sqlite3_stmt *stmt;int rc = sqlite3_prepare_v2(db, [update UTF8String], -1, &stmt, nil);if (rc == SQLITE_OK) {    if (sqlite3_step(stmt) == SQLITE_ROW) {        update = [NSString stringWithFormat:@"UPDATE LIST SET COUNT = ?, NAME = ?, DATE = ?, IDNUM = ? WHERE IDNUM = '%i'", [accessID integerValue]];    }    else{        update = [NSString stringWithFormat:@"INSERT OR REPLACE INTO LIST (COUNT, NAME, DATE, IDNUM) VALUES (?, ?, ?, ?)"];       }}

先上下面的方案吧：）

为了减少网络流量，请问我可以只拿房间GUID和状态两个字段么，呵呵。。。。

The MIN/MAX optimization＝＝＝＝＝＝＝＝＝＝＝＝＝＝＝

Queries of the following forms will be optimized to run in logarithmic time assuming appropriate indices exist:

  SELECT MIN(x) FROM table;  SELECT MAX(x) FROM table;

In order for these optimizations to occur, they must appear in exactly the form shown above - changing only the name of the table and column.It is not permissible to add a WHERE clause or do any arithmetic on the result. The result set must contain a single column. The column in the MIN or MAX function must be an indexed column.

所以我们的错误就在

select max(dd) as x,min(dd)as y from dd where state=4／／本来测试没有看where，后来用了where发现不对了。这。。。。！