技术很差，写了好久，怎么才能实现模糊查询

    private void btnSearch_ItemClick(object sender, ItemClickEventArgs e)
    {
        string str = txtInfo.ToString();
        string whereClause = (_ResultLayer as IFeatureLayerDefinition).DefinitionExpression;
        string tableName = StaticSystemAOClass.AOComm.GetDataSetName(_ResultLayer.FeatureClass);
        string sql = string.Format("select  * from {0} where ZLXZ like ",str);
        DataTable dt = WFSysParaClass.SysDbCtrl.GetDataTable(sql);
        this.gvMain.CollapseAllGroups();
        this.gcMain.DataSource = dt;


    }

string sql = string.Format("select * from {0} where ZLXZ like ?","%"+str+"%");