DECODE and CASE statements in Oracle both provide a conditional construct, similar to an IF-THEN-ELSE statement. However, there are some key differences between the two.
DECODE
DECODE is a function that takes three arguments:
- Expression: The expression to evaluate.
- Search: The value to search for.
- Result: The value to return if the expression matches the search value.
If the expression does not match the search value, DECODE will return the optional Else Result value, or NULL if the Else Result value is not specified.
CASE
CASE is a statement that takes a variable number of arguments, in pairs:
- Condition: The condition to evaluate.
- Result: The value to return if the condition is true.
The CASE statement will evaluate the conditions in order, and return the first result for a condition that is true. If none of the conditions are true, the CASE statement will return the optional Else Result value, or NULL if the Else Result value is not specified.
Differences between DECODE and CASE
Feature DECODE CASE Type Function Statement Logical operators Equality only Equality and other logical operators Predicates and subqueries Scalar values only Predicates and subqueries in searchable form PL/SQL Not supported Supported Function/procedure parameter Not supported Supported Datatype consistency Not required Required NULL handling Different from CASE Same as CASE ANSI SQL compliance No Yes Performance Slower Faster
Examples
The following example shows how to use DECODE to compare a value to multiple possible values:
SQLSELECT DECODE(salary, 100000, 'High', 50000, 'Medium', 'Low') AS salary_category
FROM employees;
This query will return the following results:
SALARY_CATEGORY
----------------
High
Medium
Low
The following example shows how to use CASE to compare a value to multiple possible values and to return different results based on the comparison:
SQLSELECT CASE salary
WHEN 100000 THEN 'High'
WHEN 50000 THEN 'Medium'
ELSE 'Low'
END AS salary_category
FROM employees;
This query will return the same results as the previous example.
When to use DECODE and CASE
In general, CASE is the preferred choice over DECODE. It is more powerful, flexible, and efficient. However, there are some cases where DECODE may be more appropriate, such as when you need to compare a value to a single possible value or when you need to use DECODE in a PL/SQL procedure.
Here are some additional tips for choosing between DECODE and CASE:
- Use CASE if you need to perform complex logical comparisons.
- Use CASE if you need to use predicates or subqueries in your conditional statement.
- Use CASE if you need to use the conditional statement in a PL/SQL procedure.
- Use CASE if you need to pass the conditional statement as a parameter to a function or procedure.
- Use CASE if you need to ensure datatype consistency in your conditional statement.
- Use DECODE if you need to compare a value to a single possible value.
- Use DECODE if you need to use the conditional statement in a SQL statement that does not support CASE.
DECODE and CASE statements in Oracle both provide a conditional construct, similar to an IF-THEN-ELSE statement. However, there are some key differences between the two.
DECODE
DECODE is a function that takes three arguments:
- Expression: The expression to evaluate.
- Search: The value to search for.
- Result: The value to return if the expression matches the search value.
If the expression does not match the search value, DECODE will return the optional Else Result value, or NULL if the Else Result value is not specified.
CASE
CASE is a statement that takes a variable number of arguments, in pairs:
- Condition: The condition to evaluate.
- Result: The value to return if the condition is true.
The CASE statement will evaluate the conditions in order, and return the first result for a condition that is true. If none of the conditions are true, the CASE statement will return the optional Else Result value, or NULL if the Else Result value is not specified.
Differences between DECODE and CASE
Feature | DECODE | CASE |
---|---|---|
Type | Function | Statement |
Logical operators | Equality only | Equality and other logical operators |
Predicates and subqueries | Scalar values only | Predicates and subqueries in searchable form |
PL/SQL | Not supported | Supported |
Function/procedure parameter | Not supported | Supported |
Datatype consistency | Not required | Required |
NULL handling | Different from CASE | Same as CASE |
ANSI SQL compliance | No | Yes |
Performance | Slower | Faster |
Examples
The following example shows how to use DECODE to compare a value to multiple possible values:
SELECT DECODE(salary, 100000, 'High', 50000, 'Medium', 'Low') AS salary_category
FROM employees;
This query will return the following results:
SALARY_CATEGORY
----------------
High
Medium
Low
The following example shows how to use CASE to compare a value to multiple possible values and to return different results based on the comparison:
SELECT CASE salary
WHEN 100000 THEN 'High'
WHEN 50000 THEN 'Medium'
ELSE 'Low'
END AS salary_category
FROM employees;
This query will return the same results as the previous example.
When to use DECODE and CASE
In general, CASE is the preferred choice over DECODE. It is more powerful, flexible, and efficient. However, there are some cases where DECODE may be more appropriate, such as when you need to compare a value to a single possible value or when you need to use DECODE in a PL/SQL procedure.
Here are some additional tips for choosing between DECODE and CASE:
- Use CASE if you need to perform complex logical comparisons.
- Use CASE if you need to use predicates or subqueries in your conditional statement.
- Use CASE if you need to use the conditional statement in a PL/SQL procedure.
- Use CASE if you need to pass the conditional statement as a parameter to a function or procedure.
- Use CASE if you need to ensure datatype consistency in your conditional statement.
- Use DECODE if you need to compare a value to a single possible value.
- Use DECODE if you need to use the conditional statement in a SQL statement that does not support CASE.
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