使用 MySQL 检查空字段

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Yes, what you are doing is correct. You are checking to make sure the email field is not an empty string. NULL means the data is missing. An empty string "" is a blank string with the length of 0.

You can add the null check also

AND (email != "" OR email IS NOT NULL)

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An empty field can be either an empty string or a NULL.

To handle both, use:

email > ''

which can benefit from the range access if you have lots of empty email record (both types) in your table.

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There's a difference between an empty string (email != "") and NULL. NULL is null and an Empty string is something.

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This will work but there is still the possibility of a null record being returned. Though you may be setting the email address to a string of length zero when you insert the record, you may still want to handle the case of a NULL email address getting into the system somehow.

     $aUsers=$this->readToArray('
SELECT `userID`
FROM `users`
WHERE `userID`
IN(SELECT `userID`
FROM `users_indvSettings`
WHERE `indvSettingID`=5 AND `optionID`='.$time.')
AND `email` != "" AND `email` IS NOT NULL
');

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If you want to find all records that are not NULL, and either empty or have any number of spaces, this will work:

LIKE '%\ '

Make sure that there's a space after the backslash. More info here: http://dev.mysql.com/doc/refman/5.0/en/string-comparison-functions.html

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You could use

IFNULL(email, '') > ''

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check this code for the problem:

$sql = "SELECT * FROM tablename WHERE condition";


$res = mysql_query($sql);


while ($row = mysql_fetch_assoc($res)) {


foreach($row as $key => $field) {


echo "<br>";


if(empty($row[$key])){


echo $key." : empty field :"."<br>";


}else{


echo $key." =" . $field."<br>";


}
}
}