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

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 ...)

SELECT column_name FROM table_name WHERE column_name IN (NULL, '')

Get rows with NULL, 0, '', ' ', ' '

    SELECT * FROM table WHERE some_col IS NOT TRUE;

Get rows without NULL, 0, '', ' ', ' '

    SELECT * FROM table WHERE some_col IS TRUE;

This statement is much cleaner and more readable for me:

select * from my_table where ISNULL(NULLIF(some_col, ''));

Another method without WHERE, try this..

Will select both Empty and NULL values

SELECT ISNULL(NULLIF(fieldname,''))  FROM tablename

Check for null

$column is null
isnull($column)

Check for empty

$column != ""

However, you should always set NOT NULL for column,
mysql optimization can handle only one IS NULL level

A shorter way to write the condition:

WHERE some_col > ''

Since null > '' produces unknown, this has the effect of filtering out both null and empty strings.

try

SELECT 0 IS NULL ,  '' IS NULL , NULL IS NULL

-> 0, 0, 1

or

SELECT ISNULL('  ') , ISNULL( NULL )
 -> 0 ,1

Reference

In my case, space was entered in the column during the data import and though it looked like an empty column its length was 1. So first of all I checked the length of the empty looking column using length(column) then based on this we can write search query

SELECT * FROM TABLE WHERE LENGHT(COLUMN)= 0;

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;

While checking null or Empty value for a column in my project, I noticed that there are some support concern in various Databases.

Every Database doesn't support TRIM method.

Below is the matrix just to understand the supported methods by different databases.

The TRIM function in SQL is used to remove specified prefix or suffix from a string. The most common pattern being removed is white spaces. This function is called differently in different databases:

• MySQL: TRIM(), RTRIM(), LTRIM()
• Oracle: RTRIM(), LTRIM()
• SQL Server: RTRIM(), LTRIM()

How to Check Empty/Null :-

Below are two different ways according to different Databases-

The syntax for these trim functions are:

1. Use of Trim to check-

   SELECT FirstName FROM UserDetails WHERE TRIM(LastName) IS NULL

2. Use of LTRIM & RTRIM to check-

   SELECT FirstName FROM UserDetails WHERE LTRIM(RTRIM(LastName)) IS NULL

Above both ways provide same result just use based on your DataBase support. It Just returns the FirstName from UserDetails table if it has an empty LastName

Hoping this will help you :)

try this if the datatype are string and row is null

SELECT * FROM table WHERE column_name IS NULL OR column_name = ''

if the datatype are int or column are 0 then try this

SELECT * FROM table WHERE column_name > = 0

Either

SELECT IF(field1 IS NULL or field1 = '', 'empty', field1) as field1 from tablename

or

SELECT case when field1 IS NULL or field1 = ''
        then 'empty'
        else field1
   end as field1 from tablename

You can also do

SELECT * FROM table WHERE column_name LIKE ''

The inverse being

SELECT * FROM table WHERE column_name NOT LIKE ''

If you want to have NULL values presented last when doing an ORDER BY, try this:

SELECT * FROM my_table WHERE NULLIF(some_col, '') IS NULL;

You can test whether a column is null or is not null using WHERE col IS NULL or WHERE col IS NOT NULL e.g.

SELECT myCol 
FROM MyTable 
WHERE MyCol IS NULL 

In your example you have various permutations of white space. You can strip white space using TRIM and you can use COALESCE to default a NULL value (COALESCE will return the first non-null value from the values you suppy.

e.g.

SELECT myCol
FROM MyTable
WHERE TRIM(COALESCE(MyCol, '')) = '' 

This final query will return rows where MyCol is null or is any length of whitespace.

If you can avoid it, it's better not to have a function on a column in the WHERE clause as it makes it difficult to use an index. If you simply want to check if a column is null or empty, you may be better off doing this:

SELECT myCol
FROM MyTable
WHERE MyCol IS NULL OR MyCol =  '' 

See TRIM COALESCE and IS NULL for more info.

Also Working with null values from the MySQL docs

I hate messy fields in my databases. If the column might be a blank string or null, I'd rather fix this before doing the select each time, like this:

UPDATE MyTable SET MyColumn=NULL WHERE MyColumn='';
SELECT * FROM MyTable WHERE MyColumn IS NULL

This keeps the data tidy, as long as you don't specifically need to differentiate between NULL and empty for some reason.

select * from table where length(RTRIM(LTRIM(column_name))) > 0

SELECT * FROM tbl WHERE trim(IFNULL(col,'')) <> '';