Select the SQL Statement will list the first name, last name and calculate the number of years the staff member has been employed.

Question

BlackTom AI · Accepted Answer

Using SQLite's Julian-day values gives an easy way to convert a date difference in days to years. The correct statement uses strftime('%J', ...) for both the current date and the hire_date, subtracts to get days employed, divides by 365 to convert to years, and rounds the result.

1) Relevant knowledge points and concepts
- strftime('%J', date) returns the Julian day number (a numeric day count) for the given date in SQLite.
- 'now' passed to strftime gives the current date/time.
- Subtracting two Julian-day values yields the number of days between dates.
- Dividing by 365 converts days to approximate years.
- round(...) rounds the calculated years to the nearest integer.
- SQL aliasing AS YEARS_HIRED labels the computed column.

2) Step-by-step reasoning
- Compute current Julian day: Jnow = strftime('%J','now').
- Compute hire Julian day: Jhire = strftime('%J',hire_date).
- Days employed = Jnow - Jhire.
- Years employed = (Jnow - Jhire) / 365.
- Round the result and return with first_name and last_name.

3) Intermediate calculation example
- Suppose Jnow = 2459000, Jhire = 2457000.
- Days employed = 2459000 - 2457000 = 2000 days.
- Years = 2000 / 365 ≈ 5.479.
- round(5.479) = 5 → YEARS_HIRED = 5.

4) Why the correct answer is correct
- The provided correct option exactly follows the above steps: it uses strftime('%J','now') minus strftime('%J',hire_date), divides by 365, and rounds the result, returning first_name, last_name and the computed alias YEARS_HIRED. This produces the intended years employed.

5) Why other options are incorrect
- The second option mixes now() (which returns a datetime string) with strftime('%J',hire_date) incorrectly and has parentheses placement issues; it won’t reliably compute Julian-day difference.
- The fourth option reverses the subtraction (strftime('%J',hire_date) - strftime('%J','now')), producing negative day counts (negative years).
- The third option is an image placeholder and not a SQL statement.

6) Conclusion
The statement SELECT first_name , last_name, round((strftime('%J','now')- strftime('%J',hire_date)) / 365 ) AS YEARS_HIRED FROM staff; is correct and matches the provided answer.

Select the SQL Statement will list the first name, last name and calculate the number of years the staff member has been employed.单项选择题

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