How to Check If a Column Is Empty or Null in MySQL

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

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

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

How to check if field is null or empty in MySQL?

Either use

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

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

If you only want to check for null and not for empty strings then you can also use ifnull() or coalesce(field1, 'empty'). But that is not suitable for empty strings.

MySQL - Which way is better to check if a column is null or empty

Evaluating the two expressions on a single row should not take such a big difference. The reason people use the second version is the use of indexes. Mysql has a special optimization for this and can use it even with the or.

See IS NULL Optimization

IS NULL Optimization
MySQL can perform the same optimization on col_name IS NULL that it can use for col_name = constant_value. For example, MySQL can use indexes and ranges to search for NULL with IS NULL.
If a WHERE clause includes a col_name IS NULL condition for a column that is declared as NOT NULL, that expression is optimized away. This optimization does not occur in cases when the column might produce NULL anyway; for example, if it comes from a table on the right side of a LEFT JOIN.
MySQL can also optimize the combination col_name = expr OR col_name IS NULL, a form that is common in resolved subqueries. EXPLAIN shows ref_or_null when this optimization is used.

Check if MySQL Column is empty

If it's empty, it should output all the bets from a user. The code posted is in a for loop.

Since you are checking if it's empty, your if statement should be the other way round:

if ($row['status'] == '') {

Alternatively, you can use mysqli_num_rows() get the number of rows:

Returns the number of rows in the result set.

$result = queryMysql("SELECT * FROM bets WHERE user='$user'");

if (mysqli_num_rows($result) > 0) {
$row = mysqli_fetch_array($result);
    echo  "Status: " . $status . "

" .
    "Published by: " . $user . "
" .
    "PICK: " . $pick . "
" .
    "Odds: " . $odds . "
" .
    "Stake: " . $stake . "
" .
    nl2br($analysis) ;
}

Also, there isn't such function called queryMysql():

$result = queryMysql("SELECT * FROM bets WHERE user='$user'");

It should be mysqli_query(). For mysqli_query(), the connection parameter is needed.

$result = mysqli_query($conn, "SELECT * FROM bets WHERE user='$user'");

How to check if more than one column is empty or NULL

You should organize your query with parenthesis:

SELECT * 
FROM product
WHERE (isstock IS NULL OR isstock = '')
  AND (iscon IS NULL OR iscon = '')

If we add the parenthesis to your original query as they are by default:

isstock IS NULL OR
(isstock = '' AND iscon IS NULL) OR
iscon = ''

So without the ()'s it means totally different.

In mysql you can do this as well:

SELECT * 
FROM product
WHERE
    ifnull(isstock,'') = '' 
   AND
    ifnull(iscon,'') = ''

Maybe this is a bit cleaner.

Checking if a column is not null or empty

I think this is clearer

COALESCE(v.file_name,'') != '' AND COALESCE(v.file_last_known_location,'') != ''

On some systems this may perform worse (as @sgeddes notes) against indexed columns.

Check whether a column is empty

Check whether it is null or empty string.

 Select * FROM Items WHERE Extra IS NULL OR Extra = ''

How to check if a column is empty in SQL

SELECT * FROM order WHERE user_fk = $user_fk AND invoice is null or invoice = '';

Try this if invoice supports null