Question

如何优化此SQL查询？

Private Sub cmb1_AfterUpdate()
    Me.cmb2.RowSource = ""
    Me.cmb2.Value = ""
    Me.cmb3.RowSource = ""
    Me.cmb3.Value = ""

    Dim strSQL As String

    If IsNull(cmb1) = False Then
        strSQL = "Select ID_Group " & _
        "From Tbl_Mst_Group " & _
        "Where ID_License = '" & Me.cmb1 & "'"

        Me.cmb2.RowSource = strSQL
        Me.cmb2.Requery
     Else
        Me.cmb2.RowSource = ""
        Me.cmb2.Value = ""
        Me.cmb3.RowSource = ""
        Me.cmb3.Value = ""
    End If

Private Sub cmb2_AfterUpdate()

    Dim strSQL As String

    If IsNull(cmb2) = False Then
        strSQL = "Select ID_SubGroup " & _
                 "From Tbl_Mst_SubGroup " & _
                 "Where ID_Group = '" & Me.cmb2 & "'"
        Me.cmb3.RowSource = strSQL
        Me.cmb3.Requery
    Else
        Me.cmb3.RowSource = ""
        Me.cmb3.Value = ""
    End If
End Sub

如果有一种方法可以减少“ where”条件的写入，那就没问题了。

Answer 1

首先，WHERE子句中的三个条件实际上是联接条件的一部分，并且应该正确地出现在ON子句中，并带有现代显式联接。考虑以下版本：

SELECT 
    ec.code_element, 
    ec.code_caracteristique, 
    ec.valeur_texte, 
    ec.valeur_num, 
    ec.valeur_date, 
    ec.index_tableau, 
    ec.valeur_liste,
    e.code_type_element
FROM ods_element_caracteristique ec
INNER JOIN ods_element e
    ON e.code = ec.code_element
INNER JOIN ods_caracteristique c
    ON c.name = ec.code_caracteristique
INNER JOIN ods_modele_caracteristique mc
    ON c.idmodele_caracteristique = mc.id 
WHERE
    mc.idtype_valeur != 6   AND
    ec.valeur_liste IS NULL AND
    ec.code_caracteristique != 'TE_GENER_DATE_MES';

通过升级到现代联接语法，它还减小了WHERE子句的大小。

Answer 2

以较少的“ where”条件写出来

您是说缩短它而不改变它的含义吗？

WHERE 
  (e.code, c.name, c.idmodele_caracteristique) = (ec.code_element, ec.code_caracteristique, mc.id) 
  AND (mc.idtype_valeur, ec.code_caracteristique) != (6, 'TE_GENER_DATE_MES')

如何优化此SQL查询以减少连接？

2 个答案: