如何使用SQL查询从多个表中获取最早的日期？

Question

How to use SQL query to get earliest Date from multiple Tables?

Summary (Revised on 10 Jan 2016): I need info from 3 Tables (A, B, C), TableC has no primary key, hence I will get multiple [C_Date] record for each [B_ID].

' Description of Database:
'    A Ms Access database file: "c:\DB\Data.mdb"
'    It has 3 Tables: [TableA], [TableB], [TableC]
'    TableA with Fields [A_ID], [A_Design]
'    TableB with Fields [B_ID], [A_ID], [B_InventoryNum], [B_BlankNum] 
'    TableC with Fields [B_ID], [C_Name], [C_Value], [C_Date] 
'    TableA Primary Key is [A_ID]
'    TableB Primary Key is [B_ID]
'    TableC has no Primary Key, hence, for each [B_ID], there are multiple [C_Date]

Below is one example of the data from TableC
B_ID    Name    Value       C_Date
73    Diamter    35.375     27-Jan-98
73    Diamter    35.376     27-Jan-98
73    Diamter    35.375     12-Apr-98
73    Diamter    35.374     19-Jul-98
73    Diamter    35.374     23-Sep-98
73    Diamter    35.374     30-Mar-99
73    Diamter    35.375     24-Oct-99
73    Diamter    35.374     24-Oct-99
73    Height     22.491     27-Jan-98
73    Height     21.908     12-Apr-98
73    Height     21.908     19-Jul-98
73    Height     21.915     23-Sep-98
73    Height     21.901     30-Mar-99
73    Height     21.909     24-Oct-99
73    Height     22.041     27-Jan-98

The Query Sequence is as follow:

1. Use where [A_Design] LIKE '%99%' to Get [A_ID] From TableA  
2. Use 'Left Join' to link to TableB
3. Use 'Left Join' again to link to TableC

'Left Join' is just an example, it can be replaced by 'Inner Join'.

My current Sql query will return all the 15 rows for a B_ID (73), but I just need a single date - the earliest date (27-Jan-98), I am also not interested in other fields, such as [Name], [Value].

The following codes in VB.NET will retrieve multiple [C_Date]. If I only want the earliest [C_Date], how shall I modify my SQL script? Any suggestion and feedback would be greatly appreciated!

If you are not interested in VB.NET, please jump directly to Sql string, the question is for SQL syntax, which is independent from any specific programming language.

Many thanks to @PhilipXY and @Rory for the suggestion to test only within the Access environment, example codes and informative guides, finally my problem got solved.

Below SQL is a working copy from the MS Access SQL View of a Query.

SELECT Distinct [TableA].[A_Design], [TableA].A_ID, [TableB].B_ID, [TableB].B_InventoryNum, [TableB].[B_BlankNum], [TableC].C_Date, [TableC].B_ID FROM ([TableA] INNER JOIN [TableB] ON [TableA].A_ID = [TableB].B_ID) INNER JOIN [TableC] ON [TableB].B_ID = [TableC].B_ID GROUP BY [TableA].[A_Design], [TableA].A_ID, [TableB].B_ID, [TableB].B_InventoryNum, [TableB].[B_BlankNum], [TableC].C_Date, [TableC].B_ID HAVING ((([TableA].[A_Design]) Like ' 99 ') AND (([TableC].C_Date)=(SELECT TOP 1 Min([TableC].C_Date) FROM [TableC] Where [TableC].B_ID=[TableB].B_ID)));

With this revised SQL, now I am able to retrieve the following info from TableC:

B_ID    C_Date
73    27-Jan-98

Problem solved! I would like to vote 5 for both @PhilipXY and @Rory. ( I assume that 5 is the highest point I can vote.)

VB.NET Codes:    
================================================================
    Imports System.Data.OleDb
    Imports System.Windows.Forms
    ' 1. Just add a DataGridView1 control on your winform,
    ' 2. then add a button (Named: 'btnTest')
    ' 3. Below is the button click handler, it will retrieve info from database and display it on the "DataGridView1" control.

Private Sub btnTest_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnTest.Click

    Dim MDBConnString_ As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\DB\Data.mdb;"
    Dim cnn As OleDbConnection = New OleDbConnection(MDBConnString_)
    cnn.Open()

    Dim Sql As String
    Sql = "SELECT " & "([A_Design]+Format([B_InventoryNum],""0000"")) AS DesignCodePK, [TableA].[A_ID], [A_Design], [TableB].[B_ID], [B_InventoryNum], [B_BlankNum], [C_Date] FROM ([TableA] LEFT JOIN [TableB] On [TableA].[A_ID] = [TableB].[A_ID]) " & " LEFT JOIN [TableC] On [TableB].[B_ID] = [TableC].[B_ID] Where [A_Design] LIKE '%99%' Order by [A_Design], [B_InventoryNum], [C_Date] "

    Dim cmd As New OleDbCommand(Sql, cnn)
    Dim DataAdapter As New OleDbDataAdapter(cmd)
    Dim ds As System.Data.DataSet
    ds = New System.Data.DataSet

    DataAdapter = New OleDbDataAdapter(cmd)
    DataAdapter.Fill(ds, "joined")
    DataGridView1.DataSource = ds.Tables("joined")
    cnn.Close()
End Sub

Answer 1

To get the min date for a B_ID use

select min(c_date) from TableC where b_id = XXXX

To get all the min dates

select b_id, min(c_date) as MinDate
from TableC group by b_id

You can then join that query on to other tables:

select *
from TableB
left join (
    select b_id, min(c_date) as MinDate
    from TableC group by b_id
) as minimumDates
    on minimumDates.b_id = TableB.b_id

If you're having trouble with query syntax try to run your SQL against MS Access directly rather than via VB. That'll make it easier to check what does/doesn't work. If you can't get the GROUP BY to work then start with a new query as simple as possible, like with my first select above. Forget which columns you really want, just get a simple query working and then add JOIN s and WHERE and columns one at a time.