为什么运行后单击时只能全部查询，选COBID.TEXT却没有作用？

Private Sub Command1_Click()
Dim rs As New ADODB.Recordset
sql = "select myid as 序号, contractname AS 合同名称,clientname as 签署单位 , signing_time as 签署时间,amount as 合同金额, payment as 已付金额, unpaid as 未付金额, memo as 备注 from mycontract_managerment"
If Me.Option1.Value Then
If cboID.Text = "" Then
MsgBox "请输入合同名称"
cboID.SetFocus
Exit Sub
Else
sql = sql & " where contractname = " & cboID.Text

End If
End If

rs.Open sql, conn

Set Me.MSHFlexGrid1.DataSource = rs
rs.Close
Exit Sub
End Sub

sql语句的问题

把

sql = "select myid as 序号, contractname AS 合同名称,clientname as 签署单位 , signing_time as 签署时间,amount as 合同金额, payment as 已付金额, unpaid as 未付金额, memo as 备注 from mycontract_managerment"

改成

sql = "select myid as 序号, contractname AS 合同名称,clientname as 签署单位 , signing_time as 签署时间,amount as 合同金额, payment as 已付金额, unpaid as 未付金额, memo as 备注 like '" & cboID.Text & "' from mycontract_managerment"

最近比较忙，不能玩问问啦。抱歉！