Month: March 2020

Adv Database Management: SQL Group functions

Please note that the following blog post provides a summary view for what you need to get done (left column) and quick examples that illustrate how to do it in SQL (right column with SQL code in red). For more information please see the resources below:

AVG, COUNT, MAX, MIN, STDDEV, SUM, VARIANCE 
SELECT AVG(sal), MAX(sal), MIN(sal), SUM(sal)
  FROM emp
  WHERE jobs LIKE ‘Sales%’
COUNT 
SELECT COUNT(*)
  FROM emp
  WHERE deptno = 30
Group By 
SELECT deptno, AVG(sal)
  FROM emp
  GROUP BY deptno
Rollup and cube 
SELECT   deptno, MAX(sal)
  FROM     emp
  GROUP BY deptno WITH ROLLUP [CUBE]
Having 
SELECT   deptno, MAX(sal)
  FROM     emp
  GROUP BY deptno
  HAVING max(sal)>2900

 

Database Management: SQL Joins

Please note that the following blog post provides a summary view for what you need to get done (left column) and quick examples that illustrate how to do it in SQL (right column with SQL code in red). For more information please see the resources below:

Equijoins 
SELECT e.ename, e.deptno,  d.deptno, d.name
  FROM emp e INNER JOIN dept d
  ON e.deptno = d.deptno
Non-Equijoins 
SELECT e.ename, e.sal,  s.grade
  FROM emp e INNER JOIN salgrade s
  WHERE e.sal
  BETWEEN  s.losal  AND  s.hisal

From:
grade      losal        hisal
-----      -----        ------
1            700        1200
2           1201        1400
3           1401        2000
4           2001        3000
5           3001        9999

Gives the following solution:
ename           sal     grade
----------   --------- ---------
JAMES            950         1
SMITH            800         1
ADAMS           1100         1
Outer joins 
SELECT e.ename, e.deptno,  d.deptno
  FROM emp e RIGHT JOIN dept d
  ON e.deptno = d.deptno

SELECT e.deptno,  d.deptno, d.name
  FROM emp e LEFT JOIN dept d
  ON e.deptno = d.deptno
Self Joins 
SELECT worker.ename +’ works for’+ manager.ename
  FROM emp worker, emp manger
  ON worker.mgr = manager.empno