New To MySql Nested Query

I have 2 tables that I'm trying to pull data from:

• USER
• USER_NAME

USER has the following indexes:

• ID
• ORG_ID
• DEFAULT_EMAIL_ID
• STATUS
• NAME
• CREATED
• UPDATED

USER_NAME has the following indexes:

• ID
• USER_ID
• STATUS
• TIMEZONE_ID
• DST
• LANG
• USERNAME
• PASSWD
• BACKEND
• REGISTERED

My goal is to get USERNAME from USER_NAME and NAME from USER. My background is more in DB2. I'm just learning MySQL. I tried the following with no luck.

select NAME from OST_USER where ID in (select ID, USERNAME from OST_USER_ACCOUNT where CREATED < '2015-07-09');

Any idea what I can do to get the info? Is it even possible with the given indexes? Any help is really appreciated!