Question

我想写一个查询，用于选择状态1＆amp;的第一条记录。状态2的第二记录等等

我喜欢

+----+--------+--------+
| id |   name | status |
+----+--------+--------+
|  1 |   ABC  |      1 |
|  2 |   PQR  |      1 |
|  3 |   qqq  |      2 |
|  4 |   www  |      1 |
|  5 |   eee  |      2 |
|  6 |   rrr  |      2 |
|  7 |   ttt  |      2 |
+----+--------+--------+

我需要一个如下所示的输出

+----+-------+---------+
| id |  name |  status |
+----+-------+---------+
|  1 |   ABC |       1 |
|  3 |   qqq |       2 |
|  2 |   PQR |       1 |
|  5 |   eee |       2 |
|  4 |   www |       1 |
|  6 |   rrr |       2 |
|  7 |   ttt |       2 |
+----+-------+---------+

记录序列应该是那样的

- 1st record with status 1
- 2nd record with status 2
- 3rd record with status 1
- 4th record with status 2
- 5th record with status 1
- 6th record with status 2

状态为2的第7条记录 - ＆gt;如果我们找不到状态为1的记录，则选择状态为2＆amp;的记录。反之亦然

我通过编码得到了这个输出但是MySQL查询可能得到这样的输出

Answer 1

您可以使用变量：

SELECT id, name, status
FROM (
   SELECT id, name, status,
       @grp := IF(@status = status, @grp + 1, 
                  IF(@status := status, 1, 1)) AS grp
   FROM mytable
   CROSS JOIN (SELECT @grp := 0, @status := 0) AS vars
   ORDER BY status, name) AS t
ORDER BY grp, status, name

使用的算法中的关键是变量@grp：它基本上模拟ROW_NUMBER() OVER (PARTITION BY status)。使用@grp，我们可以通过交替 status效果轻松实现顺序。

Demo here

Answer 2

procedure InitializeWizard();
var
  CustomStatusLabel: TNewStaticText;
begin
  WizardForm.FilenameLabel.Visible := False;
  WizardForm.StatusLabel.Visible := False;

  WizardForm.ProgressGauge.Top := WizardForm.InstallingPage.Height - ScaleY(60);

  CustomStatusLabel := TNewStaticText.Create(WizardForm);
  CustomStatusLabel.Parent := WizardForm.InstallingPage;
  CustomStatusLabel.Caption := 'Installing Colectica';
  CustomStatusLabel.Font.Size := CustomStatusLabel.Font.Size + 4;
  CustomStatusLabel.Font.Style := [fsBold];
  CustomStatusLabel.AutoSize := True;
  CustomStatusLabel.Top :=
    WizardForm.ProgressGauge.Top - CustomStatusLabel.Height - ScaleY(8);
  CustomStatusLabel.Left :=
    WizardForm.ProgressGauge.Left +
    ((WizardForm.ProgressGauge.Width - CustomStatusLabel.Width) div 2);
end;

Answer 3

您可以使用此查询SELECT rownum FROM TABLE GROUP BY rownum HAVING mod(rownum,2)=0

MySql写入查询选择状态1＆amp;的第一条记录第二个状态记录2，依此类推

3 个答案: