COALESCE(열이름, null일때 넣을 내용)을 사용해준다
SELECT COALESCE(name,0) FROM table참고문서
https://dangdo.tistory.com/59
https://jieun0113.tistory.com/136
https://pingfanzhilu.tistory.com/entry/PostgreSQL-NULLIF-%ED%95%A8%EC%88%98%EB%A5%BC-%EC%82%AC%EC%9A%A9%ED%95%98%EC%97%AC-Null-%EB%B0%8F-%EA%B3%B5%EB%B0%B1-%EC%B2%98%EB%A6%AC%ED%95%98%EB%8A%94-%EB%B0%A9%EB%B2%95with-Oracle-MySQL-MSSQL
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