CASE statements in OBIEE

Conditional Expressions

Expressions are building blocks for creating conditional expressions that convert a value from one form to another. Expressions

include:

·         CASE (Switch)

·         CASE (If)

CASE (Switch)

This form of the CASE statement is also referred to as the CASE(Lookup) form. The value of expr1 is examined, then the WHEN expressions. If expr1 matches any WHEN expression, it assigns the value in the corresponding THEN expression.

If none of the WHEN expressions match, it assigns the default value specified in the ELSE expression. If no ELSE expression is specified, the system automatically adds an ELSE NULL.

If expr1 matches an expression in multiple WHEN clauses, only the expression following the first match is assigned.

Note: In a CASE statement, AND has precedence over OR.

Syntax

CASE expr1
     WHEN expr2 THEN expr3
     {WHEN expr... THEN expr...}
     ELSE expr
END

Where:

CASE starts the CASE statement. Must be followed by an expression and one or more WHEN and THEN statements, an optional ELSE statement, and the END keyword.

WHEN specifies the condition to be satisfied.
THEN specifies the value to assign if the corresponding WHEN expression is satisfied.
ELSE specifies the value to assign if none of the WHEN conditions are satisfied. If omitted, ELSE NULL is assumed.
END ends the CASE statement.

Example

CASE Score-par
  WHEN -5 THEN 'Birdie on Par 6'
  WHEN -4 THEN 'Must be Tiger'
  WHEN -3 THEN 'Three under par'
  WHEN -2 THEN 'Two under par'
  WHEN -1 THEN 'Birdie'
  WHEN 0 THEN 'Par'
  WHEN 1 THEN 'Bogey'
  WHEN 2 THEN 'Double Bogey'
  ELSE 'Triple Bogey or Worse'
END

In this example, the WHEN statements must reflect a strict equality. For example, a WHEN condition of WHEN < 0 THEN 'Under Par' is illegal because comparison operators are not allowed.

CASE (If)

This form of the CASE statement evaluates each WHEN condition and if satisfied, assigns the value in the corresponding THEN expression.

If none of the WHEN conditions are satisfied, it assigns the default value specified in the ELSE expression. If no ELSE expression is

specified, the system automatically adds an ELSE NULL.

Note: In a CASE statement, AND has precedence over OR.

Syntax

CASE 
     WHEN request_condition1 THEN expr1
     {WHEN request_condition2 THEN expr2}
     {WHEN request_condition... THEN expr...}
     ELSE expr
END 

Where:

CASE starts the CASE statement. Must be followed by one or more WHEN and THEN statements, an optional ELSE statement, and the END keyword.

WHEN specifies the condition to be satisfied.
THEN specifies the value to assign if the corresponding WHEN expression is satisfied.
ELSE specifies the value to assign if none of the WHEN conditions are satisfied. If omitted, ELSE NULL is assumed.

END ends the CASE statement.

Example

CASE
  WHEN score-par < 0 THEN 'Under Par'
  WHEN score-par = 0 THEN 'Par'
  WHEN score-par = 1 THEN 'Bogie'
  WHEN score-par = 2 THEN 'Double Bogey'
  ELSE 'Triple Bogey or Worse'
END

Unlike the Switch form of the CASE statement, the WHEN statements in the If form allow comparison operators. For example, a WHEN

condition of WHEN < 0 THEN 'Under Par' is legal.

Using a FILTER Function Instead of CASE Statements

Let’s face it; CASE statements are notorious for causing poor query performance. For certain kinds of simple CASE statements, there may be a more performance-friendly OBIEE alternative – the FILTER function. Like CASE statements, you can use the FILTER function to build a logical column expression. In the Expression Builder, this function can be found under Functions > Display Functions > Filter. Here is an example of how to use it:
Suppose you have two Logical Columns derived from the following expressions:

• Southern Region Units:
  CASE WHEN Paint.Markets.Region = ‘SOUTHERN REGION’ THEN Paint. SalesFacts.Units ELSE 0 END
• Western Region Units:
  CASE WHEN Paint.Markets.Region = ‘WESTERN REGION’ THEN Paint. SalesFacts.Units ELSE 0 END

Instead of using CASE statements, try using the following equivalent expressions involving the FILTER function:

• Southern Region Units:
  FILTER(Paint. SalesFacts.Units USING Paint.Markets.Region = ‘SOUTHERN REGION’)
• Western Region Units:
  FILTER(Paint. SalesFacts.Units USING Paint.Markets.Region = ‘WESTERN REGION’)

The SQL generated by the FILTER expressions will typically perform better than the SQL generated from the CASE statements. The FILTER SQL may look something like this (pretending all the columns come from the same physical table):

SELECT Year,
SUM(CASE WHEN Region = ‘SOUTHERN REGION’ THEN Units),
SUM(CASE WHEN product = ‘WESTERN REGION’ THEN Units)
FROM physical_table
WHERE Region = ‘SOUTHERN REGION’ OR Region = ‘WESTERN REGION’
GROUP BY year

The SQL generated from the CASE statements may look more like this:

SELECT Year,
SUM(CASE WHEN Region = ‘SOUTHERN REGION’ THEN Units ELSE 0),
SUM(CASE WHEN product = ‘WESTERN REGION’ THEN Units ELSE 0)
FROM physical_table
GROUP BY year

The major difference is that the FILTER SQL includes the criteria in the WHERE clause. In most cases, this means that the WHERE clause would run first, constraining the result set before the CASE statements are run, hence the improvement in performance.

Article From: http://www.biconsultinggroup.com/obiee-tips-and-tricks/using-a-filter-function-instead-of-case-statements.html