008.Oracle数据库 , 判断字段内容是否为空

/*Oracle数据库查询日期在两者之间*/
SELECT 
    PKID, OCCUR_DATE, ATA
FROM
    LM_FAULT 
WHERE
    ( 
      ( OCCUR_DATE >= to_date( '2017-05-01', 'yyyy-MM-DD' ) ) AND 
      ( OCCUR_DATE <= to_date( '2017-05-15', 'yyyy-MM-DD' ) ) AND 
        ( ATA IS NULL)  
    );

效果如下：​ ​