MySQL CONCAT returns NULL if any field contain NUL

问题:

I have following data in my table "devices"

affiliate_name  affiliate_location  model     ip             os_type    os_version 

cs1             inter               Dell     10.125.103.25   Linux      Fedora  
cs2             inter               Dell     10.125.103.26   Linux      Fedora  
cs3             inter               Dell     10.125.103.27   NULL       NULL    
cs4             inter               Dell     10.125.103.28   NULL       NULL    

I executed below query

SELECT CONCAT(`affiliate_name`,'-',`model`,'-',`ip`,'-',`os_type`,'-',`os_version`) AS device_name
FROM devices

It returns result given below

cs1-Dell-10.125.103.25-Linux-Fedora
cs2-Dell-10.125.103.26-Linux-Fedora
(NULL)
(NULL)

How to come out of this so that it should ignore NULL AND result should be

cs1-Dell-10.125.103.25-Linux-Fedora
cs2-Dell-10.125.103.26-Linux-Fedora
cs3-Dell-10.125.103.27-
cs4-Dell-10.125.103.28-

回答1:

convert the NULL values with empty string by wrapping it in COALESCE

SELECT CONCAT(COALESCE(`affiliate_name`,''),'-',COALESCE(`model`,''),'-',COALESCE(`ip`,''),'-',COALESCE(`os_type`,''),'-',COALESCE(`os_version`,'')) AS device_name
FROM devices

回答2:

Use CONCAT_WS instead:

CONCAT_WS() does not skip empty strings. However, it does skip any NULL values after the separator argument.

SELECT CONCAT_WS('-',`affiliate_name`,`model`,`ip`,`os_type`,`os_version`) AS device_name FROM devices

回答3:

SELECT CONCAT(isnull(`affiliate_name`,''),'-',isnull(`model`,''),'-',isnull(`ip`,''),'-',isnull(`os_type`,''),'-',isnull(`os_version`,'')) AS device_name
FROM devices

回答4:

To have the same flexibility in CONCAT_WS as in CONCAT (if you don't want the same separator between every member for instance) use the following:

SELECT CONCAT_WS("",affiliate_name,':',model,'-',ip,... etc)

回答5:

CONCAT_WS still produces null for me if the first field is Null. I solved this by adding a zero length string at the beginning as in CONCAT_WS("",affiliate_name,'-',model,'-',ip,'-',os_type,'-',os_version) however CONCAT("",affiliate_name,'-',model,'-',ip,'-',os_type,'-',os_version) produces Null when the first field is Null.

回答6:

you can use if statement like below

select CONCAT(if(affiliate_name is null ,'',affiliate_name),'- ',if(model is null ,'',affiliate_name)) as model from devices