VB6 x MySQL - SELECT from two databases - Just one connection - (pt-BR: SELECT em dois bancos)

English:
Considering that your databases are both on the same server/instance, yes, you can get fields from two or more databases.
Remember: 
-for this example you are using MyODBC 3.51 like me (MySQL 32bits, so, MyODBC 32bits);
-your data source name is "store" and was properly set up;
-Reference: Microsoft ActiveX Data Objects 2.5 library

Português:
SELECT em dois bancos (desde que estejam no mesmo servidor e instância do MySQL)
Considere:
-Para este exemplo, estou usando o MyODBC 3.51 (MySQL de 32 bits, ODBC de 32bits)
-Referenciar: Microsoft ActiveX Data Objects 2.5 library
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Raw/didactic code (please, read this twice)

Private Sub getItemDescription(code as string)
Dim sql As String
sql = "SELECT dbStore.itens.description from dbCentral.itens, dbStore.itens " _
    + "WHERE dbStore.itens.BarCode = dbCentral.itens.BarCode " _
    + "AND dbStore.itens.BarCode = '" & code &  "';"
    
Dim con As ADODB.Connection
Dim table As New ADODB.Recordset

Set con = New ADODB.Connection
con.Open "Provider=MSDASQL.1;Persist Security Info=False;" _ 
          + "Data Source=store; Database=dbStore" 
table.Open sql, con

If Not (table.EOF) Then
    MsgBox table!description
End If

con.Close
set con = Nothing
End Sub
'-------------------------------------

If you are not using DSN (but MyODBC):
(pt-BR: Se não estiver usando Data Source Name, somente MyODBC)

Private Sub getItemDescription(code as string)
Dim sql As String
sql = "SELECT dbStore.itens.description from dbCentral.itens, dbStore.itens " _
    + "WHERE dbStore.itens.BarCode = dbCentral.itens.BarCode " _
    + "AND dbStore.itens.BarCode = '" & code &  "';"

    Dim cn As ADODB.Connection
    Dim mySQLConString As String
    Dim tbl As New ADODB.Recordset
    
    mySQLConString = "DRIVER={MySQL ODBC 3.51 Driver};" _
           + "SERVER=localhost;user=root;password=1234;" _
           + "Persist Security Info=False;Encrypt=yes"

    Set cn = New ADODB.Connection
    cn.Open (mySQLConString)
    
    tbl.Open sql, cn
    
    If Not (tbl.EOF) Then
        MsgBox tbl!description
    End If
    
    cn.Close
    Set cn = Nothing
End Sub

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Question: Why VB6?
Answer: just legacy code