concat() usage

  

SELECT school_code,`name`,phone from student WHERE login_name REGEXP 'ning$'LIMIT 10;

            

 concat()

• SELECT CONCAT(school_code,`name`) from student WHERE login_name REGEXP 'ning$' LIMIT 10;

           

• SELECT CONCAT(school_code,`name`,phone) from student WHERE login_name REGEXP 'ning$' LIMIT 10; (one field is null, the result of concat is null)

          

  CONCAT_WS()

• SELECT CONCAT_WS('-',school_code,NAME,login_name,phone) from student WHERE login_name REGEXP 'ning$' LIMIT 10;

           

•  SELECT `name`,MIN(id) FROM student GROUP BY `name` HAVING COUNT(id) >=2 LIMIT 10;

          

 GROUP_CONCAT()

• SELECT school_code,`name` from student WHERE `name`='刘媛媛' LIMIT 10;

        

• SELECT NAME,GROUP_CONCAT(id) from student WHERE `name`='刘媛媛' LIMIT 10;

           

•  SELECT NAME,GROUP_CONCAT(id) FROM student GROUP BY `name` HAVING COUNT(id) >=2 LIMIT 10;