Question

我需要一个关于My Sql Query的帮助..

我的表就像这样

_id studid  recid   arrival
834 29     436      12:04
835 29     437      12:19
836 29     438      12:35
837 29     439      12:43

现在我需要比较recid 436和recid 439

的ID

完全像这样

  _id(recid(436)) < _id(recid(439)) // 834 < 837 (true)

我需要查询...

我试过这个..

public boolean Check(String tid,String src,String dest)
{
    Cursor c1 = this.db.query(TABLE_NAME_2, new String[] { "_id" },
            "_studId = \"" + src +"\"  AND _recId = \"" + tid+"\"" , null, null, null, null);

    Cursor c2 = this.db.query(TABLE_NAME_2, new String[] { "_id" },
            "_studId = \"" + dest +"\"  AND _recId = \"" + tid+"\"" , null, null, null, null);
    int srcid = 0;
    int destid = 0;

    if (c1.moveToFirst()) 
    {
          do {
              srcid = Integer.parseInt(c1.getString(0));
           } while (c1.moveToNext());
    }
    if (c1 != null && !c1.isClosed()) {
         c1.close();
    }
    if (c2.moveToFirst()) 
    {
        do {
            destid = Integer.parseInt(c2.getString(0));
        } while (c2.moveToNext());
    }
    if (c2 != null && !c2.isClosed()) {
        c1.close();
    }   
    if(srcid < destid)
    {
        return true;
    }
    else
    {
        return false;
    }
}

在这样检查时返回正确的结果

 System.out.println(dh.Check("29", "436", "439")); // returns true.

但我认为它不正确的程序，因为会有多个记录。所以如果有50条记录，那么我必须执行这个功能50次。所以我需要一个简单的查询..

如果有任何身体有这样的经历。请帮帮我..

先谢谢。

Answer 1

你可以使用这样的查询，它返回0或1：

SELECT (SELECT _id FROM MyTable WHERE recid = 436) <
       (SELECT _id FROM MyTable WHERE recid = 439)

要使重复执行更有效，请使用预编译语句，您可以使用不同参数执行多次：

SQLiteStatement stmt = db.compileStatement(
    "SELECT (SELECT _id FROM MyTable WHERE studid = ? AND recid = ?) < "+
           "(SELECT _id FROM MyTable WHERE studid = ? AND recid = ?)");
...
int recid_src = 436;
int recid_dst = 439;
int studid = 29;
stmt.bindLong(1, studid);
stmt.bindLong(2, recid_src);
stmt.bindLong(3, studid);
stmt.bindLong(4, recid_dst);
boolean result = stmt.simpleQueryForLong() != 0;

MySql查询用于将同一表的Id与diff记录进行比较

1 个答案: