FROM 中的子查詢必須具有 sql 查詢的別名

Question

我有這個代碼片段用於下面的查詢。

"SELECT DISTINCT(CODE) FROM (" +
    "SELECT TRIM(BOTH ' ' FROM PROJECT_NUMBER) CODE FROM SCHEMA.TABLE_NAME " +
    "WHERE PROJECT_NUMBER IS NOT NULL " +
    "AND LAST_UPDATE_DATE >= :lastUpdateDate " +
"UNION " +
    "SELECT TRIM(BOTH ' ' FROM ANOTHER_CODE) CODE FROM SCHEMA.TABLE_NAME " +
    "WHERE ANOTHER_CODE IS NOT NULL " +
    "AND LAST_UPDATE_DATE >= :lastUpdateDate " +
") " +
"WHERE CODE IS NOT NULL";

我正在從 oracle 遷移到 postgres，我在日志中看到了這些錯誤：

Caused by: org.postgresql.util.PSQLException: ERROR: subquery in FROM must have an alias
  Hint: For example, FROM (SELECT ...) [AS] foo.

別名 go 應該在哪里，我是否需要所有子查詢，我是否需要在此查詢中使用別名？ 這里有點困惑。

Answer 1

"SELECT DISTINCT(CODE) FROM (" +
    "SELECT TRIM(BOTH ' ' FROM PROJECT_NUMBER) CODE FROM SCHEMA.TABLE_NAME " +
    "WHERE PROJECT_NUMBER IS NOT NULL " +
    "AND LAST_UPDATE_DATE >= :lastUpdateDate " +
"UNION " +
    "SELECT TRIM(BOTH ' ' FROM ANOTHER_CODE) CODE FROM SCHEMA.TABLE_NAME " +
    "WHERE ANOTHER_CODE IS NOT NULL " +
    "AND LAST_UPDATE_DATE >= :lastUpdateDate " +
") as qry " +
"WHERE CODE IS NOT NULL";