LEAD

Returns the value from a subsequent row in the result set.

See also: LAG

Syntax

LEAD(
    expression
    [, offset ]
    [, default ]
)
OVER (
    [ PARTITION BY partition_expression ]
    ORDER BY sort_expression
)

Arguments:

• expression: The column or expression to evaluate
• offset: Number of rows after the current row (default: 1)
• default: Value to return when no next row exists (default: NULL)

Notes:

• Negative offset values work like LAG function
• Returns NULL if the offset goes beyond partition boundaries

Examples

-- Create sample data
CREATE TABLE scores (
    student VARCHAR(20),
    test_date DATE,
    score INT
);

INSERT INTO scores VALUES
    ('Alice', '2024-01-01', 85),
    ('Alice', '2024-02-01', 90),
    ('Alice', '2024-03-01', 88),
    ('Bob', '2024-01-01', 78),
    ('Bob', '2024-02-01', 82),
    ('Bob', '2024-03-01', 85);

Get next test score for each student:

SELECT student, test_date, score,
       LEAD(score) OVER (PARTITION BY student ORDER BY test_date) AS next_score
FROM scores
ORDER BY student, test_date;

Result:

student | test_date  | score | next_score
--------+------------+-------+-----------
Alice   | 2024-01-01 |    85 | 90
Alice   | 2024-02-01 |    90 | 88
Alice   | 2024-03-01 |    88 | NULL
Bob     | 2024-01-01 |    78 | 82
Bob     | 2024-02-01 |    82 | 85
Bob     | 2024-03-01 |    85 | NULL

Get score from 2 tests later:

SELECT student, test_date, score,
       LEAD(score, 2, 0) OVER (PARTITION BY student ORDER BY test_date) AS score_2_tests_later
FROM scores
ORDER BY student, test_date;

Result:

student | test_date  | score | score_2_tests_later
--------+------------+-------+--------------------
Alice   | 2024-01-01 |    85 | 88
Alice   | 2024-02-01 |    90 | 0
Alice   | 2024-03-01 |    88 | 0
Bob     | 2024-01-01 |    78 | 85
Bob     | 2024-02-01 |    82 | 0
Bob     | 2024-03-01 |    85 | 0