How do I check if a column is empty or null in MySQL?

Question

I have a column in a table which might contain null or empty values. How do I check if a column is empty or null in the rows present in a table?

(e.g. null or '' or '  ' or '      ' and ...) 

Answer 1

This will select all rows where some_col is NULL or '' (empty string)

SELECT * FROM table WHERE some_col IS NULL OR some_col = ''; 

Answer 2

As defined by the SQL-92 Standard, when comparing two strings of differing widths, the narrower value is right-padded with spaces to make it is same width as the wider value. Therefore, all string values that consist entirely of spaces (including zero spaces) will be deemed to be equal e.g.

'' = ' ' IS TRUE '' = '  ' IS TRUE ' ' = '  ' IS TRUE '  ' = '      ' IS TRUE etc 

Therefore, this should work regardless of how many spaces make up the some_col value:

SELECT *    FROM T  WHERE some_col IS NULL         OR some_col = ' '; 

or more succinctly:

SELECT *    FROM T  WHERE NULLIF(some_col, ' ') IS NULL;