mysql CONCAT、CONCAT_WS、GROUP_CONCAT（）

1、CONCAT（）

Function for connecting the plurality of strings into a single string.

SELECT CONCAT(id,'-',sex) AS a FROM recruitment_requirement    condition: id sex and must be non-null

SELECT CONCAT(id,'-',centre_id) AS id_sex FROM recruitment_requirement   note: id still non-null, but centre_id is null, the result of a problem

 

2、CONCAT_WS()

Representative CONCAT With Separator, is CONCAT () is a special form.

The first parameter is the other argument separator. Positions separator placed between two strings to be connected. The separator can be a string or other parameters. If the separator is NULL, the result to NULL. NULL function ignores any parameter values ​​delimiter. But CONCAT_WS () will not ignore any empty string, but will ignore all NULL).

SELECT CONCAT_WS('-',id,sex) AS id_sex FROM recruitment_requirement     id sex with a non-null

SELECT CONCAT_WS('-',id,centre_id) AS id_sex FROM recruitment_requirement  id non-null, but is null centre_id

. 3, the GROUP_CONCAT ()
the GROUP_CONCAT function returns a string result, which is connected by a value in the packet combination.

(Id non-null, but it centre_id be null) SELECT GROUP_CONCAT(id) FROM recruitment_requirement  SELECT id,GROUP_CONCAT(id) FROM recruitment_requirement  SELECT GROUP_CONCAT(centre_id) FROM recruitment_requirement   SELECT id,GROUP_CONCAT(centre_id) FROM recruitment_requirement