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我是新的iphone开发人员。我有一个sql查询“select pubdate from test where rowid in(select max(rowid)from test)”。当我执行这个查询我没有得到适当的结果。 源代码:通过使用单个语句执行多个查询来获得最大值
NSString *query=[NSString stringWithFormat:@"select pubdate from %@ where rowid in(select max(rowid) from %@)",tableName,tableName];
const char * sql = [query UTF8String];
sqlite3_stmt *lastInsVal_statement = nil;
NSArray * paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,NSUserDomainMask, YES);
NSString * docsDir = [paths objectAtIndex:0];
NSString * thePath = [docsDir stringByAppendingPathComponent:
@"Training_Project2.sqlite"];
sqlite3_open([thePath UTF8String], &database);
sqlite3_prepare_v2(database, sql, -1, &lastInsVal_statement, NULL);
NSString* pubdate;
while(sqlite3_step(lastInsVal_statement)==SQLITE_ROW){
const char* str = (const char*)sqlite3_column_text(lastInsVal_statement, 2);
pubdate = [NSString stringWithCString:str encoding:NSUTF8StringEncoding];
}
sqlite3_finalize(lastInsVal_statement);
sqlite3_close(database);
return pubdate;
sqlite3_column_text(lastInsVal_statement,2);似乎是问题,因为您只选择一列,可能应该是sqlite3_column_text(lastInsVal_statement,0)。 – Mohammad
您可以将没有子查询的查询写为'SELECT pubdate FROM test ORDER BY rowid DESC LIMIT 1'。 –