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

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