谁知道怎么做组合查询进行搜索？不在SQL里写~在C#里拼接条件

string sqlStr="select * from [TABLE] where";

if(textbox1.text.trim()!="")
{
sqlStr += "field = '"+textbox1.text.trim()+"' And "
}
if(textbox2.text.trim()!="")
{
sqlStr += "field = '"+textbox2.text.trim()+"' And "
}

sqlStr=sqlStr.Substring(0,sqlStr.Length-5);