mysql和oracle数据库获取为Null的值变为0

oracle: 

SELECT
  ar."ID",
  ar."USER_ID" userId,
  ar."CONTENT" content,
  ar."IMAGE" image,
  ar."CREATE_DATE" createDate,
  ar."UPDATE_DATE" updataDate,
"NVL"(ac.RECORD_NUM, 0)  recordNum,
  au.XM userName
  FROM

用 "NVL"(expr1, expr2) 

expr1 为查出来的字段  expr2 为转换的字段

mysql:

case when ac.RECORD_NUM is null then 0 else ac.RECORD_NUM end as RECORD_NUM,