Which of the following questions is answered by the SQL statement?

SELECT COUNT (Product_Description) FROM Product_T;

Question

Which of the following questions is answered by the SQL statement?

SELECT COUNT (Product_Description) FROM Product_T;

BlackTom AI · Accepted Answer

COUNT(Product_Description) returns the number of non-NULL values in the Product_Description column. This is the key SQL behavior to know: COUNT(column_name) counts only rows where that specific column is not NULL; COUNT(*) counts all rows regardless of NULLs in columns; COUNT(DISTINCT column_name) counts distinct non-NULL values.

Step-by-step reasoning:
1. Interpret the statement: SELECT COUNT (Product_Description) FROM Product_T; asks the database to count entries in the Product_Description column of table Product_T.
2. Apply the COUNT(column) rule: each row contributes 1 to the count only if Product_Description is not NULL; rows with NULL descriptions are ignored.
3. Illustrative example: if Product_T has 6 rows and Product_Description values are ['Pen', 'Pencil', NULL, 'Eraser', 'Marker', NULL], then COUNT(Product_Description) = 4 because there are four non-NULL descriptions. Show intermediate step: total rows = 6, NULL descriptions = 2, non-NULL = 6 − 2 = 4.
4. Therefore the returned value answers how many products have product descriptions recorded in the Product_T table.

Why the correct answer is correct:
- The statement directly counts non-NULL product descriptions, so it measures how many products have descriptions.

Why the other options are incorrect:
- "How many characters are in the field name 'Product_Description'?" is wrong because character-length functions (e.g., LENGTH or CHAR_LENGTH) operate on strings, not COUNT.
- "How many different columns named 'Product_Description' are there in table Product_T?" is metadata-related and not returned by COUNT; SQL metadata queries (INFORMATION_SCHEMA) are needed.
- "How many products are in the table Product_T?" would require COUNT(*) or COUNT(primary_key); COUNT(Product_Description) can be lower if some descriptions are NULL.

Conclusion: The SQL returns how many products have product descriptions in the Product Table, matching the provided correct answer.

Which of the following questions is answered by the SQL statement? SELECT COUNT (Product_Description) FROM Product_T; 单项选择题

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