Question

我目前有两个表，其中versionLog可以包含许多ProductVersions。

以下Sql查询：

    private List<Bind> _Registers = new List<Bind>();
private ModbusClient modbusClient;
private void Form1_Load(object sender, EventArgs e)
{
    modbusClient = new ModbusClient("10.54.11.252", 502);
    modbusClient.Connect();
    int[] ReadValues = modbusClient.ReadHoldingRegisters(0, 1);
    for(var i = 0; i < ReadValues.length; i++)
    {
      Registers.Add(new Bind()
        {
            Value = ReadValues[i];
        });
    }
    txt40001.DataBindings.Add(new Binding("Text", Registers[0],
     "Value", true, DataSourceUpdateMode.OnPropertyChanged));
}
public List<Bind> Registers
{
    get
    {
        return _Registers;
    }

    set
    {
        _Registers = value;
    }
}

产生类似于

的结果集

SELECT
versionlog.[Name],
(
    SELECT COUNT(*) 
    FROM dbo.ProductVersions productVersion 
    WHERE productVersion.VersionLogId = versionLog.Id  
) AS ProductVersions
FROM dbo.Versionlog versionLog

等等。

如何限制结果集仅返回ProductVersion Count = 0的Versionlog？

根据google，我需要使用Name | ProductVersions Log1  | 12 Log2  |  6 Log3  |  0子句吗？

Answer 1

使用HAVING：

SELECT versionlog.[Name]
FROM dbo.Versionlog versionLog
LEFT JOIN dbo.ProductVersions productVersion 
  ON productVersion.VersionLogId = versionLog.Id  
GROUP BY versionlog.[Name]
HAVING COUNT(productVersion.VersionLogId) = 0;

且未分组：

SELECT versionlog.[Name]
FROM dbo.Versionlog versionLog
LEFT JOIN dbo.ProductVersions productVersion 
  ON productVersion.VersionLogId = versionLog.Id  
WHERE productVersion.VersionLogId IS NULL

Answer 2

另一种子查询

select * from 
(
SELECT
versionlog.[Name],
(
    SELECT COUNT(*) 
    FROM dbo.ProductVersions productVersion 
    WHERE productVersion.VersionLogId = versionLog.Id  
) AS ProductVersions
FROM dbo.Versionlog versionLog
) a where a.ProductVersions=0

筛选计数子句-一对多关系

2 个答案: