LayerDefinition模糊查询无效？

pFeatureLayer.Name = pFeatureLayer.FeatureClass.AliasName;
IFeatureLayerDefinition pFeatureLayerDefinition = pFeatureLayer as IFeatureLayerDefinition;

pFeatureLayerDefinition.DefinitionExpression = "DWDM = '" + DWDM + "'";
//pFeatureLayerDefinition.DefinitionExpression = "DWDM like '" + DWDM + "%'";

pFeatureLayer = (IFeatureLayer)pFeatureLayerDefinition;
map.AddLayer(pFeatureLayer);
 
以上代码可得到结果
换成注释的代码就无效