CS457 Syllabus & Progress

`DISTINCT` and the "*" selector

DISTINCT.

SQL outputs by default duplicate values, for example:


   SELECT name   
   FROM   dependent                                


   Output:

         NAME
         ----------
	 Alice
	 Abner
	 Alice
	 Elizabeth
	 Joy
	 Micheal
	 Theodore

To remove duplicate values, use the DISTINCT keyword in the SELECT clause:


   SELECT DISTINCT name                      
   FROM   dependent 


   Output:

      NAME
      ----------
      Alice
      Theodore
      Joy
      Abner
      Micheal
      Elizabeth

NOTE:

The * SELECTOR.

The SELECT * clause will select all attributes in the relations in the FROM clause

Example:


    SELECT *
    FROM   department
    WHERE  dname = 'Research';


  Output:

      DNAME              DNUMBER MGRSSN    MGRSTARTDA
      --------------- ---------- --------- ----------      
      Research                 5 333445555 22-MAY-78

DISTINCT and the "*" selector

`DISTINCT` and the "*" selector