Oracle CASE SQL statement

Don Burleson

•

The CASE statement is like a series of IF statements, only using the key word WHEN. A CASE statement is evaluated from top to bottom. If a condition is true, then corresponding THEN clause is executed and execution jumps to the END CASE (short circuit evaluation) clause.

Consider this pseudo-code example:

case
when n_numb = 1 then v_status := 'very small'
when n_numb < 4 then v_status := 'small'
when n_numb = 5 then v_status := 'even'
when n_numb > 4 then v_status := 'large'
else v_status := 'very large'
end case;

Oracle SQL allows you to add "Boolean logic" and branching using the decode and CASE clauses. The case statement is a more flexible extension of the Decode statement. In its simplest form the Oracle CASE function is used to return a value when a match is found:

SELECT last_name, commission_pct,  
(CASE commission_pct     
WHEN 0.1 THEN 'Low'     
WHEN 0.15 THEN 'Average'    
WHEN 0.2 THEN 'High'     
ELSE 'N/A'   END ) Commission
FROM 
   employees 
ORDER BY 
   last_name;

•

A more complex version is the Searched CASE expression where a comparison expression is used to find a match:

SELECT last_name, job_id, salary,
  (CASE
    WHEN job_id LIKE 'SA_MAN' AND salary < 12000 THEN '10%' or %% added in the end.
    WHEN job_id LIKE 'SA_MAN' AND salary >= 12000 THEN '15%'
    WHEN job_id LIKE 'IT_PROG' AND salary < 9000 THEN '8%'
    WHEN job_id LIKE 'IT_PROG' AND salary >= 9000 THEN '12%'
    ELSE 'NOT APPLICABLE'
  END ) Raise
FROM employees;

Read more on Boolean logic:

The PL/SQL IF Statement

Use a CASE Statement in Oracle SQL

* CASE 1: Books with total sales greater than $100,000, display "Best Seller"

* CASE 2: Books with total sales between $10,000 and $99,999 display "Average Seller"

* CASE 3: Books with sales less than $10,000 display "Poor Seller"

ANSWER:

col store_name format a25
col book_title format a25
col total_sales format $999,999
col sales format a15

break on sales skip 2

select
(case
   when sum(quantity)*book_retail_price > 100000 then 'Best Seller'
   when sum(quantity)*book_retail_price < 10000 then 'Poor Seller'
   else 'Average Seller'
   end ) sales,
   store_name,
   book_title,
   sum(quantity)*book_retail_price total_sales
from
   store,
   sales,
   book
where
   store.store_key = sales.store_key
and
   sales.book_key = book.book_key
group by
   store_name,
   book_title,
   book_retail_price
order by
   total_sales desc
;

Get the Complete
Oracle SQL Tuning Information

The landmark book "Advanced Oracle SQL Tuning The Definitive Reference" is filled with valuable information on Oracle SQL Tuning. This book includes scripts and tools to hypercharge Oracle 11g performance and you can buy it for 30% off directly from the publisher.

��