SELECT DISTINCT
SELECT DISTINCT DEPT_NO
FROM EMP
WHERE (SELECT COUNT (*)
FROM EMP EMP1
WHERE EMP1.DEPT_NO = EMP.DEPT_NO) = 30;
Введение в модель данных SQL
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SELECT DISTINCT DEPT_NO
FROM EMP
WHERE (SELECT COUNT (*)
FROM EMP EMP1
WHERE EMP1.DEPT_NO = EMP.DEPT_NO) = 30;