mysql的case when字段为空,null的问题

SELECT CASE WHEN name is null THEN '该字段为空' ELSE name END as name ,email_id FROM mysql_table_name

SELECT (case when cdi.DEVICE_TAG is not null then cdi.DEVICE_TAG else '暂无数据' end) as deviceTag, (case when cdi.DEVICE_CODE is not null then cdi.DEVICE_CODE else '暂无数据' end) as deviceCode, (case when sc.full_name is not null then sc.full_name else '暂无数据' end) as deviceVendor, (case when ct.CLASS_NAME is not null then ct.CLASS_NAME else '暂无数据' end) as deviceTypeNameB, (case when cdi.DEVICE_PORT is not null then cdi.DEVICE_PORT else '暂无数据' end) as devicePort, (case when cdi.CREATE_TIME is not null then cdi.CREATE_TIME else '暂无数据' end) as createTimeStr -- 			cdi.DEVICE_TAG as deviceTag, -- 			cdi.DEVICE_CODE as deviceCode, -- 			sc.full_name as deviceVendor, -- 			ct.CLASS_NAME as deviceTypeNameB, -- 			cdi.DEVICE_PORT as devicePort, -- 			cdi.CREATE_TIME as createTimeStr FROM con_device_info AS cdi LEFT JOIN sys_code AS sc ON sc.code_value = cdi.DEVICE_VENDOR LEFT join con_type as ct on ct.ID=cdi.DEVICE_TYPE where cdi.ID=#{id}