[Solved] Given the table numbers with column num containing values (1, 2, 4, 5, 7), what will the following query return?SELECT num, LEAD(num) OVER (ORDER BY num) AS next_num FROM numbers; | SQL

SQL - Advanced Query Patterns

Given the table numbers with column num containing values (1, 2, 4, 5, 7), what will the following query return?

SELECT num, LEAD(num) OVER (ORDER BY num) AS next_num FROM numbers;

A[{num:1, next_num:2}, {num:2, next_num:4}, {num:4, next_num:5}, {num:5, next_num:7}, {num:7, next_num:null}]

B[{num:1, next_num:1}, {num:2, next_num:2}, {num:4, next_num:4}, {num:5, next_num:5}, {num:7, next_num:7}]

C[{num:1, next_num:3}, {num:2, next_num:4}, {num:4, next_num:6}, {num:5, next_num:7}, {num:7, next_num:null}]

D[{num:1, next_num:null}, {num:2, next_num:null}, {num:4, next_num:null}, {num:5, next_num:null}, {num:7, next_num:null}]

Step-by-Step Solution

Solution:

Step 1: Understand LEAD() output
LEAD(num) returns the next row's num value ordered by num. So each row shows its own num and the next number.
Step 2: Apply to given data
For values 1,2,4,5,7:
1's next is 2
2's next is 4
4's next is 5
5's next is 7
7 has no next, so null
Final Answer:
[{num:1, next_num:2}, {num:2, next_num:4}, {num:4, next_num:5}, {num:5, next_num:7}, {num:7, next_num:null}] -> Option A
Quick Check:
LEAD() shifts values down by one [OK]

Quick Trick: LEAD() shows next row's value or null if none [OK]

Common Mistakes:

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