How does case work in Oracle?

In a simple CASE expression, Oracle Database searches for the first WHEN THEN pair for which expr is equal to comparison_expr and returns return_expr . If none of the WHEN THEN pairs meet this condition, and an ELSE clause exists, then Oracle returns else_expr .

HOW DO CASE statements work?

The CASE statement chooses from a sequence of conditions, and executes a corresponding statement. The CASE statement evaluates a single expression and compares it against several potential values, or evaluates multiple Boolean expressions and chooses the first one that is TRUE .

What is difference between decode and case in Oracle?

CASE is a statement while DECODE is a function. CASE can work with logical operators other than ‘=’ : DECODE performs an equality check only. CASE is capable of other logical comparisons such as < ,> ,BETWEEN , LIKE etc.

How do you write a case statement in PL SQL?

Like the IF statement, the CASE statement selects one sequence of statements to execute. However, to select the sequence, the CASE statement uses a selector rather than multiple Boolean expressions. A selector is an expression, the value of which is used to select one of several alternatives.

Can I use case in where clause Oracle?

You can use a CASE expression in any statement or clause that accepts a valid expression. For example, you can use the CASE expression in statements such as SELECT , UPDATE , or DELETE , and in clauses like SELECT , WHERE , HAVING , and ORDDER BY .

Can case be used in where clause?

CASE can be used in any statement or clause that allows a valid expression. For example, you can use CASE in statements such as SELECT, UPDATE, DELETE and SET, and in clauses such as select_list, IN, WHERE, ORDER BY, and HAVING.

How must you end a CASE statement?

Simple CASE statement The selector values i.e., selector_value_1 , selector_value_2 , etc., are evaluated sequentially. If the result of a selector value equals the result of the selector , then the associated sequence of statements executes and the CASE statement ends.

What parts of a CASE statement are mandatory?

end statement
The case statement must always have an end statement associated with it. The expression used in a case statement must have an integral or enumerated type or be of a class type in which the class has a single conversion function to an integral or enumerated type. You can have any number of case statements within a case.

What are the two types of case expression?

There are two forms of case expressions:

• • Simple.
• Syntax for the searched case expression is as follows:
• Operand type and Result type: All data types, but the types of source_value,match_value1, match_value2, …
• ‘unknown’) AS state_name;
• and.

How do you end a case in Oracle?

Your SQL statement would look as follows: SELECT table_name, CASE owner WHEN ‘SYS’ THEN ‘The owner is SYS’ WHEN ‘SYSTEM’ THEN ‘The owner is SYSTEM’ END FROM all_tables; With the ELSE clause omitted, if no condition was found to be true, the CASE statement would return NULL.

How to use a case statement in Oracle?

This Oracle tutorial explains how to use the Oracle/PLSQL CASE statement with syntax and examples. The Oracle/PLSQL CASE statement has the functionality of an IF-THEN-ELSE statement. Starting in Oracle 9i, you can use the CASE statement within a SQL statement.

How does Oracle evaluate the searched CASE expression?

Like the simple CASE expression, Oracle also uses short-circuit evaluation for the searched CASE expression. In other words, Oracle evaluates each Boolean condition to determine whether it is true, and never evaluates the next condition if the previous one is true.

Can you use a case within a case in SQL?

Can You Use An SQL CASE within CASE? Yes, you can use a CASE within CASE in SQL. The examples below will show how this is done. Can I Use DECODE Instead Of CASE? Oracle has a function called DECODE, which lets you check an expression and return different values. It looks like this: DECODE (expression, condition1, result1, condition_n, result_n)

When to return else in a case expression in Oracle?

In a searched CASE expression, Oracle searches from left to right until it finds an occurrence of condition that is true, and then returns return_expr. If no condition is found to be true, and an ELSE clause exists, Oracle returns else_expr.