Mostrando colunas da tabela MYSQL com tipos de chave e referência

SELECT c.COLUMN_NAME,
       --c.COLUMN_KEY,
       IF(EXISTS(select *
                 FROM information_schema.KEY_COLUMN_USAGE k
                 JOIN information_schema.TABLE_CONSTRAINTS tc 
                   ON (k.TABLE_SCHEMA=tc.TABLE_SCHEMA 
                       AND k.TABLE_NAME=tc.TABLE_NAME 
                       AND k.CONSTRAINT_NAME=tc.CONSTRAINT_NAME)
                WHERE k.TABLE_SCHEMA=c.TABLE_SCHEMA 
                      AND k.TABLE_NAME=c.TABLE_NAME 
                      AND tc.CONSTRAINT_TYPE='PRIMARY KEY' 
                      AND c.COLUMN_NAME=k.COLUMN_NAME),'PK',null) AS PK,
       IF(EXISTS(select *
                 FROM information_schema.KEY_COLUMN_USAGE k
                 JOIN information_schema.TABLE_CONSTRAINTS tc 
                   ON (k.TABLE_SCHEMA=tc.TABLE_SCHEMA 
                      AND k.TABLE_NAME=tc.TABLE_NAME 
                      AND k.CONSTRAINT_NAME=tc.CONSTRAINT_NAME)
                WHERE k.TABLE_SCHEMA=c.TABLE_SCHEMA 
                      AND k.TABLE_NAME=c.TABLE_NAME 
                      AND tc.CONSTRAINT_TYPE='UNIQUE' 
                      AND c.COLUMN_NAME=k.COLUMN_NAME),'UQ',null) AS UQ,
       IF(EXISTS(select *
                 FROM information_schema.KEY_COLUMN_USAGE k
                 JOIN information_schema.TABLE_CONSTRAINTS tc 
                   ON (k.TABLE_SCHEMA=tc.TABLE_SCHEMA 
                      AND k.TABLE_NAME=tc.TABLE_NAME 
                      AND k.CONSTRAINT_NAME=tc.CONSTRAINT_NAME)
                WHERE k.TABLE_SCHEMA=c.TABLE_SCHEMA 
                      AND k.TABLE_NAME=c.TABLE_NAME 
                      AND tc.CONSTRAINT_TYPE='FOREIGN KEY' 
                      AND c.COLUMN_NAME=k.COLUMN_NAME),'FK',null) AS FK,
       c.EXTRA,
       c.IS_NULLABLE,
       c.DATA_TYPE,
       c.COLUMN_TYPE,
       c.CHARACTER_MAXIMUM_LENGTH,
       c.COLUMN_COMMENT,
       k.REFERENCED_TABLE_SCHEMA,
       k.REFERENCED_TABLE_NAME,
       k.REFERENCED_COLUMN_NAME
FROM information_schema.COLUMNS c
LEFT JOIN information_schema.KEY_COLUMN_USAGE k
    ON (k.TABLE_SCHEMA=c.TABLE_SCHEMA
   AND k.TABLE_NAME=c.TABLE_NAME
   AND k.COLUMN_NAME=c.COLUMN_NAME
   AND k.POSITION_IN_UNIQUE_CONSTRAINT IS NOT NULL)
 WHERE c.TABLE_SCHEMA='PHPDAO'
   AND c.TABLE_NAME='employees';