Group_Concat in Concat not working with NULL values

Question

I have a table

CREATE TABLE IF NOT EXISTS `dept` (
  `did` int(11) NOT NULL,
  `dname` varchar(50) DEFAULT NULL
) ENGINE=InnoDB DEFAULT CHARSET=latin1;

INSE         


        

Answer 1

From the MySQL aggregate function documentation:

Unless otherwise stated, group functions ignore NULL values.

Use COALESCE() to replace the nulls with a string, since they would be eliminated by the aggregate function. For example COALESCE(dbname, 'NULL') will return the string NULL if dbname IS NULL. Its purpose is to return the first non-null of the arguments you give it, and can therefore return a default value.

SELECT
  GROUP_CONCAT(CONCAT(did,"','", COALESCE(dname, 'NULL')) SEPARATOR "'),('") AS Result
FROM dept