CASE WHEN condition THEN result    [WHEN ...]    [ELSE default_result]END

Input:

One or multiple *WHENcondition THENresult clauses are used and the expression can optionally have an *ELSEdefault_result clause. Everycondition should be a boolean expression.

Output: one of theresult expressions if the corresponding *WHENcondition evaluates totrue or thedefault_result if all *WHENcondition clauses evaluate tofalse. If the optional *ELSEdefault_result clause is missing and all *WHENcondition clauses evaluate tofalse thennull is returned.

Description: The CASE expression is a generic conditional expression which simulates if/else statements of other programming languages If the condition’s result is true, the value of the result expression that follows the condition will be the returned the subsequent when clauses will be skipped and not processed.

SELECT CASE WHEN 1 > 2 THEN 'elastic'            WHEN 2 <= 3 THEN 'search'       END AS "case";    case---------------search

SELECT CASE WHEN 1 > 2 THEN 'elastic'            WHEN 2 > 10 THEN 'search'       END AS "case";    case---------------null

SELECT CASE WHEN 1 > 2 THEN 'elastic'            WHEN 2 > 10 THEN 'search'            ELSE 'default'       END AS "case";    case---------------default

As a variant, a case expression can be expressed with a syntax similar toswitch-case of other programming languages:

CASE expression     WHEN value1 THEN result1    [WHEN value2 THEN result2]    [WHEN ...]    [ELSE default_result]END

In this case it’s transformed internally to:

CASE WHEN expression = value1 THEN result1    [WHEN expression = value2 THEN result2]    [WHEN ...]    [ELSE default_result]END

SELECT CASE 5            WHEN 1 THEN 'elastic'            WHEN 2 THEN 'search'            WHEN 5 THEN 'elasticsearch'       END AS "case";    case---------------elasticsearch

SELECT CASE 5            WHEN 1 THEN 'elastic'            WHEN 2 THEN 'search'            WHEN 3 THEN 'elasticsearch'            ELSE 'default'       END AS "case";    case---------------default

CASE WHEN a = 1 THEN null     WHEN a > 2 THEN 10     WHEN a > 5 THEN 'foo'END

CASE can be used as a GROUP BY key in a query to facilitate custom bucketing and assign descriptive names to those buckets. If, for example, the values for a key are too many or, simply, ranges of those values are more interesting than every single value, CASE can create custom buckets as in the following example:

SELECT count(*) AS count,  CASE WHEN NVL(languages, 0) = 0 THEN 'zero'    WHEN languages = 1 THEN 'one'    WHEN languages = 2 THEN 'bilingual'    WHEN languages = 3 THEN 'trilingual'    ELSE 'multilingual'  END as lang_skillsFROM employeesGROUP BY lang_skillsORDER BY lang_skills;

With this query, one can create normal grouping buckets for values0, 1, 2, 3 with descriptive names, and every value>= 4 falls into themultilingual bucket.

COALESCE(    expression,    expression,    ...)

Input:

1. 1st expression
2. 2nd expression

…

Nth expression

COALESCE can take an arbitrary number of arguments.

Output: one of the expressions ornull

Description: Returns the first of its arguments that is not null. If all arguments are null, then it returnsnull.

SELECT COALESCE(null, 'elastic', 'search') AS "coalesce";    coalesce---------------elastic

SELECT COALESCE(null, null, null, null) AS "coalesce";    coalesce---------------null

GREATEST(    expression,    expression,    ...)

Input:

1. 1st expression
2. 2nd expression

…

Nth expression

GREATEST can take an arbitrary number of arguments and all of them must be of the same data type.

Output: one of the expressions ornull

Description: Returns the argument that has the largest value which is not null. If all arguments are null, then it returnsnull.

SELECT GREATEST(null, 1, 2) AS "greatest";    greatest---------------2

SELECT GREATEST(null, null, null, null) AS "greatest";    greatest---------------null

IFNULL(    expression,    expression)

Input:

1. 1st expression
2. 2nd expression

Output: 2nd expression if 1st expression is null, otherwise 1st expression.

Description: Variant ofCOALESCE with only two arguments. Returns the first of its arguments that is not null. If all arguments are null, then it returnsnull.

SELECT IFNULL('elastic', null) AS "ifnull";    ifnull---------------elastic

SELECT IFNULL(null, 'search') AS "ifnull";    ifnull---------------search

IIF(    expression,    expression,    [expression])

Input:

1. boolean condition to check
2. return value if the boolean condition evaluates totrue
3. return value if the boolean condition evaluatesfalse; optional

Output: 2nd expression if 1st expression (condition) evaluates totrue. If it evaluates tofalse return 3rd expression. If 3rd expression is not provided returnnull.

Description: Conditional function that implements the standardIF <condition> THEN <result1> ELSE <result2> logic of programming languages. If the 3rd expression is not provided and the condition evaluates tofalse,null is returned.

SELECT IIF(1 < 2, 'TRUE', 'FALSE') AS result1, IIF(1 > 2, 'TRUE', 'FALSE') AS result2;    result1    |    result2---------------+---------------TRUE           |FALSE

SELECT IIF(1 < 2, 'TRUE') AS result1, IIF(1 > 2 , 'TRUE') AS result2;    result1    |    result2---------------+---------------TRUE           |null

IIF(a = 1, 'one', IIF(a = 2, 'two', IIF(a = 3, 'three', 'many')))

ISNULL(    expression,    expression)

Input:

1. 1st expression
2. 2nd expression

Output: 2nd expression if 1st expression is null, otherwise 1st expression.

Description: Variant ofCOALESCE with only two arguments. Returns the first of its arguments that is not null. If all arguments are null, then it returnsnull.

SELECT ISNULL('elastic', null) AS "isnull";    isnull---------------elastic

SELECT ISNULL(null, 'search') AS "isnull";    isnull---------------search

LEAST(    expression,    expression,    ...)

Input:

1. 1st expression
2. 2nd expression

…

Nth expression

LEAST can take an arbitrary number of arguments and all of them must be of the same data type.

Output: one of the expressions ornull

Description: Returns the argument that has the smallest value which is not null. If all arguments are null, then it returnsnull.

SELECT LEAST(null, 2, 1) AS "least";    least---------------1

SELECT LEAST(null, null, null, null) AS "least";    least---------------null

NULLIF(    expression,    expression)

Input:

1. 1st expression
2. 2nd expression

Output:null if the 2 expressions are equal, otherwise the 1st expression.

Description: Returnsnull when the two input expressions are equal and if not, it returns the 1st expression.

SELECT NULLIF('elastic', 'search') AS "nullif";    nullif---------------elastic

SELECT NULLIF('elastic', 'elastic') AS "nullif";    nullif:s---------------null

NVL(    expression,    expression)

Input:

1. 1st expression
2. 2nd expression

Output: 2nd expression if 1st expression is null, otherwise 1st expression.

Description: Variant ofCOALESCE with only two arguments. Returns the first of its arguments that is not null. If all arguments are null, then it returnsnull.

SELECT NVL('elastic', null) AS "nvl";    nvl---------------elastic

SELECT NVL(null, 'search') AS "nvl";    nvl---------------search