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Overview

The FOR_MIN() function is used to search for a minimum in a specific column and return a value related to that minimum from another column.

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Syntax

FOR_MIN(metric, value)

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Arguments

  • metric: must be one of the following data types: INT, LONG, FLOAT, DOUBLE, DATE or TIMESTAMP
  • value: can be any data type except TEXT
The FOR_MIN() function returns NULL in the following situations:
  • There are no input rows
  • The metric column contains only NULL values
  • The value corresponding to the metric minimum value is NULL
This function also returns NaN (not-a-number) if the input contains a NaN.

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Examples

For the needs of this section, we will use a payment table that stores customer payment records, including any applied discounts: 
CREATE TABLE payments (
  paymentid int,
  customer_name text,
  price real,
  discount real);

INSERT INTO
  payments (paymentid, customer_name, price, discount)
VALUES
  (1, 'Alex', 280.12, 0.1),
  (2, NULL, 35.75, NULL),
  (3, 'Alex', 45.1, 0.05),
  (4, 'Alex', NULL, 0.4),
  (5, 'John', NULL, 0.1),
  (6, 'Bob', 50.45, 0.07),
  (7, 'Bob', 120.5, 0.0);
To view the payments table content, run the following query: 
SELECT * FROM payments;

 paymentid | customer_name | price  | discount 
-----------+---------------+--------+----------
         1 | Alex          | 280.12 |      0.1
         2 |               |  35.75 |         
         3 | Alex          |   45.1 |     0.05
         4 | Alex          |        |      0.4
         5 | John          |        |      0.1
         6 | Bob           |  50.45 |     0.07
         7 | Bob           |  120.5 |        0
(7 rows)

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FOR_MIN() basic usage

To determine the price associated with the lowest discount applied across all payments, use the following query: 
SELECT FOR_MIN(discount, price) AS for_lowest_discount FROM payments;
This query returns the following output: 
 for_lowest_discount 
---------------------
               120.5
(1 row)

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FOR_MIN() with GROUP BY clause

To determine the discount associated with the lowest price paid by each customer, we will use the GROUP BY clause with FOR_MIN() function: 
SELECT customer_name,
  FOR_MIN(price, discount) AS discount
FROM payments
GROUP BY customer_name;
This query returns the following output: 
customer_name | discount
---------------+----------
 Bob           |     0.07
 Alex          |     0.05
               |
 John          |
(4 rows)