How to find least non-null column in one particular row in SQL?

Question

I am trying to find the lowest number in two columns of a row in the same table, with the caveat that one of the columns may be null in a particular row. If one of the colum

Answer 1

This may perform a bit better (may have to be converted to corresponding MySql syntax):

SELECT
  CASE
    WHEN Col1 IS NULL THEN Col2
    WHEN Col2 IS NULL THEN Col1
    ELSE Least(Col1, Col2)
  END

Another alternative (probably slower though, but worth a try):

SELECT Col1
WHERE Col2 IS NULL
UNION
SELECT Col2
WHERE Col1 IS NULL
UNION
SELECT least(Col1, Col2)
WHERE Col1 IS NOT NULL AND Col2 IS NOT NULL

Answer 2

This is how I solved it:

select coalesce(least(col1, col2), col1, col2)

If one value is NULL, the query will return the first non-NULL value. You can even add a default value as the last parameter, if both values can be NULL.

Answer 3

Depending on your corner case situation of having all values be null, I would go for such syntax, which is more readable (An easier solution if you have exactly two columns is below!)

SELECT LEAST( IFNULL(5, ~0 >> 1), IFNULL(10, ~0 >> 1) ) AS least_date;
-- Returns: 5

SELECT LEAST( IFNULL(null, ~0 >> 1), IFNULL(10, ~0 >> 1) ) AS least_date;
-- Returns: 10

SELECT LEAST( IFNULL(5, ~0 >> 1), IFNULL(null, ~0 >> 1) ) AS least_date;
-- Returns: 5

SELECT LEAST( IFNULL(null, ~0 >> 1), IFNULL(null, ~0 >> 1)) AS least_date
-- Returns: @MAX_VALUE (If you need to use it as default value)

SET @MAX_VALUE=~0 >> 1;
SELECT LEAST( IFNULL(null, @MAX_VALUE), IFNULL(null, @MAX_VALUE)) AS least_date;
-- Returns: @MAX_VALUE (If you need to use it as default value). Variables just makes it more readable!

SET @MAX_VALUE=~0 >> 1;
SELECT NULLIF(
    LEAST( IFNULL(null, @MAX_VALUE), IFNULL(null,@MAX_VALUE)),
    @MAX_VALUE
) AS least_date;
-- Returns: NULL

That is my prefered way if

• you can ensure that at least one column cannot be NULL
• in corner case situation (all columns are NULL) you want a non-null default value which greater than any possible value or can get limited to a certain threshold
• You can deal with variables to make this statement even more readable

If you question yourself what ~0 >> 1 means: It's just a short hand for saying "Give me the greatest number available". See also: https://stackoverflow.com/a/2679152/2427579

Even better, if you have only two columns, you can use:

SELECT LEAST( IFNULL(@column1, @column2), IFNULL(@column2, @column1) ) AS least_date;
-- Returns: NULL (if both columns are null) or the least value

Answer 4

I've created a function which handles any number of dates, by concatenating them with a separator (CONCAT_WS) as first parameter to the function.

CONCAT_WS besides dynamic number of parameters, will remove all NULL dates ;)

The function accepts two parameters:

• delimiter separated string of dates as TEXT
• delimiter as TEXT (same as used on CONCAT_WS !!) - you can remove it if you use only preferred separator on CONCAT_WS.

CREATE FUNCTION `min_date`(`dates` TEXT, `delim` VARCHAR(10)) RETURNS DATE NO SQL DETERMINISTIC
BEGIN

DECLARE `result` DATE DEFAULT NULL;

DECLARE `count` TINYINT DEFAULT 0;
DECLARE `temp` DATE DEFAULT NULL;

IF `delim` IS NULL THEN SET `delim` = ','; END IF;

IF `dates` IS NOT NULL AND CHAR_LENGTH(`dates`) > 0 THEN 
  SET `count` = LENGTH(`dates`) - LENGTH(REPLACE(`dates`, `delim`, SPACE(CHAR_LENGTH(`delim`) - 1)));

  WHILE `count` >= 0 DO
    SET `temp` = SUBSTRING_INDEX(SUBSTRING_INDEX(`dates`, `delim`, `count` + 1), `delim`, -1);

    IF `result` IS NULL OR `result` > `temp` THEN SET `result` = `temp`; END IF;

    SET `count` = `count` - 1;
  END WHILE;
END IF;

RETURN `result`;

END

Then, you can use in any combination of date fields or as static strings (as long as are valid dates or NULL):

SELECT min_date(CONCAT_WS(',', `date_column_1`, NULL, '2019-03-04', `date_column_2`), ',') AS `min_date`

Answer 5

Why not set the value of one column to be equal to the other column when it's NULL?

SELECT LEAST(IFNULL(COL1, COL2), IFNULL(COL2, COL1));

with the code above, the null value will be ignored unless both are null.

e.g.

COL1 = NULL, COL2 = 5

LEAST(IFNULL(NULL, 5), IFNULL(5, NULL)) -> LEAST(5, 5) -> 5

COL1 = 3, COL2 = NULL

LEAST(IFNULL(3, NULL), IFNULL(NULL, 3)) -> LEAST(3, 3) -> 3

COL1 = NULL, COL2 = NULL

LEAST(IFNULL(NULL, NULL), IFNULL(NULL, NULL)) -> LEAST(NULL, NULL) -> NULL

Answer 6

SELECT MIN(LEAST(COALESCE(COL1, COL2), COALESCE(COL2,CO1))) WHERE COL1 IS NOT NULL AND COL2 IS NOT NULL;