Question

我正在使用以下代码

  - (int)GetTextCount
  {

    NSMutableArray *audioArray=[[NSMutableArray alloc]init];



    int count = 0;
//This method is defined to retrieve data from Database


NSString *dbPath=filePath;

sqlite3 *database;

if(sqlite3_open([dbPath UTF8String], &database) == SQLITE_OK) {

    // Setup the SQL Statement and compile it for faster access
    /*
    SELECT  (
             SELECT COUNT(*)
             FROM   tab1
             ) AS count1,
    (
     SELECT COUNT(*)
     FROM   tab2
     ) AS count2
    FROM    dual
    */


    const char *sqlStatement = "select count(*) from photo where mid=? ";
    //const char *sqlStatement = "select * from textt where mid=?";
    sqlite3_stmt *compiledStatement;


    if(sqlite3_prepare_v2(database, sqlStatement, -1, &compiledStatement, NULL) == SQLITE_OK) {

        sqlite3_bind_int(compiledStatement, 1, memoryData.memoryId);

        //(compiledStatement, 1, [header UTF8String], -1, SQLITE_TRANSIENT);

        while(sqlite3_step(compiledStatement) == SQLITE_ROW) {              
            AudioData *data=[[AudioData alloc]init];
            //create the MemoryData object to store the data of one record


            // Read the data from the result row

            int pId=sqlite3_column_int(compiledStatement, 0);
            NSLog(@"total audiosssss are %i",pId);


            //NSString *filePath=[NSString stringWithUTF8String:(char *)sqlite3_column_text(compiledStatement, 2)];


            //filePath=[self retrievePath:filePath];

            //[data setAudioId:pId];
            //[data setFilePath:filePath];
            //Store every object of MemoryData in t
            [audioArray addObject:data];


        } // end of the while


    }
    sqlite3_finalize(compiledStatement);
}
sqlite3_close(database);
return [audioArray count];
  }

要从一个表计数，但我需要计算四个表中的行，所以现在我正在做的是运行单独的查询，这会降低性能，所以我想运行一个查询从四个表中选择，请帮助如何我能这样做吗？

Answer 1

我想你想要这个查询。（对不起，如果我错了）。

SELECT (SELECT count(*) from table_1  where mid = ?) + 
       (SELECT count(*) from table_2  where mid = ?) +
       (SELECT count(*) from table_3  where mid = ?) +
       (SELECT count(*) from table_4  where mid = ?)

Answer 2

试试这个：

SELECT COUNT(*) AS MyCount, 'MyTable1Count' AS Description FROM Table1
UNION ALL 
SELECT COUNT(*) AS MyCount, 'MyTable2Count' AS Description FROM Table2
UNION ALL 
SELECT COUNT(*) AS MyCount, 'MyTable3Count' AS Description FROM Table3
UNION ALL 
SELECT COUNT(*) AS MyCount, 'MyTable4Count' AS Description FROM Table4

这将生成如下结果集：

MyCount   Description
----------------------
534      MyTable1Count
33       MyTable2Count
92843    MyTable3Count
931      MyTable4Count

Answer 3

有几种方法可以完成这项任务，

SELECT
(SELECT COUNT(DISTINCT id) FROM member) AS members,
(SELECT COUNT(DISTINCT id) FROM thread) AS threads,
(SELECT COUNT(DISTINCT id) FROM post) AS posts

或者你可以使用，

SELECT COUNT(DISTINCT member.id), COUNT(DISTINCT thread.id), COUNT(DISTINCT post.id) FROM member, thread, post;

如何计算sqlite中多个表的行数

3 个答案: