如何在MySQL中检查字段为null还是空？

我试图找出如何检查，如果一个字段是NULL或空。我有这个：

SELECT IFNULL(field1, 'empty') as field1 from tablename

我需要添加其他检查field1 != ""，例如：

SELECT IFNULL(field1, 'empty') OR field1 != ""  as field1 from tablename

任何想法如何做到这一点？

无论使用

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

要么

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

如果只想检查null而不是空字符串，则也可以使用ifnull()或coalesce(field1, 'empty')。但这不适用于空字符串。

或者，您也可以使用CASE相同的方法：

SELECT CASE WHEN field1 IS NULL OR field1 = '' 
       THEN 'empty' 
       ELSE field1 END AS field1
FROM tablename.

尝试使用nullif：

SELECT ifnull(nullif(field1,''),'empty') AS field1
  FROM tablename;

您可以使用该IFNULL功能内IF。这会短一些，并且字段名称的重复次数会更少。

SELECT IF(IFNULL(field1, '') = '', 'empty', field1) AS field1 
FROM tablename

您可以创建一个函数来简化此过程。

create function IFEMPTY(s text, defaultValue text)
returns text deterministic
return if(s is null or s = '', defaultValue, s);

使用：

SELECT IFEMPTY(field1, 'empty') as field1 
from tablename

SELECT * FROM ( 
    SELECT  2 AS RTYPE,V.ID AS VTYPE, DATE_FORMAT(ENTDT, ''%d-%m-%Y'')  AS ENTDT,V.NAME AS VOUCHERTYPE,VOUCHERNO,ROUND(IF((DR_CR)>0,(DR_CR),0),0) AS DR ,ROUND(IF((DR_CR)<0,(DR_CR)*-1,0),2) AS CR ,ROUND((dr_cr),2) AS BALAMT, IF(d.narr IS NULL OR d.narr='''',t.narration,d.narr) AS NARRATION 
    FROM trans_m AS t JOIN trans_dtl AS d ON(t.ID=d.TRANSID)
    JOIN acc_head L ON(D.ACC_ID=L.ID) 
    JOIN VOUCHERTYPE_M AS V ON(T.VOUCHERTYPE=V.ID)  
    WHERE T.CMPID=',COMPANYID,' AND  d.ACC_ID=',LEDGERID ,' AND t.entdt>=''',FROMDATE ,''' AND t.entdt<=''',TODATE ,''' ',VTYPE,'
    ORDER BY CAST(ENTDT AS DATE)) AS ta

如果您想签入PHP，则应该执行以下操作：

$query_s =mysql_query("SELECT YOURROWNAME from `YOURTABLENAME` where name = $name");
$ertom=mysql_fetch_array($query_s);
if ('' !== $ertom['YOURROWNAME']) {
  //do your action
  echo "It was filled";
} else { 
  echo "it was empty!";
}