题目内容

in SQL , the SELECT statement corresponds to which operator inrelational algebra

A. projection
B. selction
C. union
D. intersection

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更多问题

in SQL , the WHERE statement corresponds to which operator inrelational algebra

A. PROJECTION
B. SELECTION
C. UNION
D. INTERSECTION

Which word can remove duplicate tuples from the query result

A. UNIQUE
B. COUNT
C. DISTINCT
D. UNION

in the following aggregate functions, Null values are not ignored in

A. SUM(COLUMN NAME)
B. MAX(COLUMN NAME)
C. AVG(COLUMN NAME)
D. COUNT(*)

In the SQL language, which of the following operations involving null values are incorrect

AGE IS NULL
B. AGE IS NOT NULL
C. AGE=NULL
D. NOT(AGE IS NULL)