SQL Best Practice

SQL be the best language to learn.

it is widely used in all development levels.

whoever working in Front End Development or Backend and Database Profile SQL is everywhere.

— SELECT UPPER CASE LETTERS
SELECT UPPER(FIRST_NAME) FROM EMPLOYEES;

— USE COLUMNS AND TABLES ALAS WHILE JOINING MULTIPLES TABLES
SELECT E.FIRST_NAME,D.DEPARTMENT_NAME,L.CITY
FROM EMPLOYEES E
JOIN DEPARTMENTS D
ON E.DEPARTMENT_ID=D.DEPARTMENT_ID
JOIN LOCATIONS L
ON D.LOCATION_ID=L.LOCATION_ID;

— NEVER USED SELECT * ALWAYS MENTION TABLES COLUMNS IN SELECT
SELECT FIRST_NAME,LAST_NAME,SALARY,NVL(COMMISSION_PCT,’0')
FROM EMPLOYEES;

SELECT DEPARTMENT_ID,MANAGER_ID
FROM DEPARTMENTS;

— ADD COMMENTS TO ENSURE OTHER DEVEOPER / TESTER EASILY GET IDEA ABOUT A CODE

— JOINING 4 TABLES
SELECT E.FIRST_NAME,D.DEPARTMENT_NAME,J.JOB_TITLE,L.CITY
FROM EMPLOYEES E
JOIN DEPARTMENTS D
ON E.DEPARTMENT_ID=D.DEPARTMENT_ID
JOIN LOCATIONS L
ON D.LOCATION_ID=L.LOCATION_ID
JOIN JOBS J
ON E.JOB_ID=J.JOB_ID;

— SELF JOIN TO FING A MANAGER FIRST ,LAST_NAME
SELECT E.FIRST_NAME AS MFN,E.LAST_NAME AS MLN
FROM EMPLOYEES E
JOIN EMPLOYEES M
ON E.EMPLOYEE_ID=M.MANAGER_ID;