Impala conditional functions

Return type: same as the initial argument value, except that integer values are promoted to BIGINT and floating-point values are promoted to DOUBLE; use CAST() when inserting into a smaller numeric column

Usage notes:

In this form of the CASE expression, the initial value A being evaluated for each row it typically a column reference, or an expression involving a column. This form can only compare against a set of specified values, not ranges, multi-value comparisons such as BETWEEN or IN, regular expressions, or NULL.

Examples:

Although this example is split across multiple lines, you can put any or all parts of a CASE expression on a single line, with no punctuation or other separators between the WHEN, ELSE, and END clauses.

select case x
    when 1 then 'one'
    when 2 then 'two'
    when 0 then 'zero'
    else 'out of range'
  end
    from t1;

Return type: same as the initial argument value, except that integer values are promoted to BIGINT and floating-point values are promoted to DOUBLE; use CAST() when inserting into a smaller numeric column

Usage notes:

CASE expressions without an initial test value have more flexibility. For example, they can test different columns in different WHEN clauses, or use comparison operators such as BETWEEN, IN and IS NULL rather than comparing against discrete values.

CASE expressions are often the foundation of long queries that summarize and format results for easy-to-read reports. For example, you might use a CASE function call to turn values from a numeric column into category strings corresponding to integer values, or labels such as Small, Medium and Large based on ranges. Then subsequent parts of the query might aggregate based on the transformed values, such as how many values are classified as small, medium, or large. You can also use CASE to signal problems with out-of-bounds values, NULL values, and so on.

By using operators such as OR, IN, REGEXP, and so on in CASE expressions, you can build extensive tests and transformations into a single query. Therefore, applications that construct SQL statements often rely heavily on CASE calls in the generated SQL code.

Because this flexible form of the CASE expressions allows you to perform many comparisons and call multiple functions when evaluating each row, be careful applying elaborate CASE expressions to queries that process large amounts of data. For example, when practical, evaluate and transform values through CASE after applying operations such as aggregations that reduce the size of the result set; transform numbers to strings after performing joins with the original numeric values.

Examples:

Although this example is split across multiple lines, you can put any or all parts of a CASE expression on a single line, with no punctuation or other separators between the WHEN, ELSE, and END clauses.

select case
    when dayname(now()) in ('Saturday','Sunday') then 'result undefined on weekends'
    when x > y then 'x greater than y'
    when x = y then 'x and y are equal'
    when x is null or y is null then 'one of the columns is null'
    else null
  end
    from t1;

Return type: same as the initial argument value, except that integer values are promoted to BIGINT and floating-point values are promoted to DOUBLE; use CAST() when inserting into a smaller numeric column

• The corresponding result when a match is found.
• The first corresponding result if there are more than one matching search expressions.
• The default expression if none of the search expressions matches the first argument expression.
• NULL if the final default expression is omitted and none of the search expressions matches the first argument.

Usage notes:

• Can be used as shorthand for a CASE expression.
• The first argument, expression, and the search expressions must be of the same type or convertible types.
• The result expression can be a different type, but all result expressions must be of the same type.
• Returns a successful match if the first argument is NULL and a search expression is also NULL.
• NULL can be used as a search expression.

Examples:

The following example translates numeric day values into weekday names, such as 1 to Monday, 2 to Tuesday, etc.

SELECT event, DECODE(day_of_week, 1, "Monday", 2, "Tuesday", 3, "Wednesday",
  4, "Thursday", 5, "Friday", 6, "Saturday", 7, "Sunday", "Unknown day")
  FROM calendar;

Return type: Same as the ifTrue argument value

Added in: Impala 1.3.0

Same as the IS FALSE operator.

Similar to ISNOTTRUE(), except it returns the opposite value for a NULL argument.

Return type: BOOLEAN

Usage notes:

In Impala 2.1.1 and higher, you can use the operators IS [NOT] TRUE and IS [NOT] FALSE as equivalents for the built-in functions ISTRUE(), ISNOTTRUE(), ISFALSE(), and ISNOTFALSE().

Same as the IS NOT FALSE operator.

Similar to ISTRUE(), except it returns the opposite value for a NULL argument.

Return type: BOOLEAN

Usage notes: Primarily for compatibility with code containing industry extensions to SQL.

Usage notes:

In Impala 2.1.1 and higher, you can use the operators IS [NOT] TRUE and IS [NOT] FALSE as equivalents for the built-in functions ISTRUE(), ISNOTTRUE(), ISFALSE(), and ISNOTFALSE().

Same as the IS NOT TRUE operator.

Similar to ISFALSE(), except it returns the opposite value for a NULL argument.

Return type: BOOLEAN

Usage notes:

In Impala 2.1.1 and higher, you can use the operators IS [NOT] TRUE and IS [NOT] FALSE as equivalents for the built-in functions ISTRUE(), ISNOTTRUE(), ISFALSE(), and ISNOTFALSE().

Compatibility notes: Equivalent to the NVL() function from Oracle Database or IFNULL() from MySQL. The NVL() and IFNULL() functions are also available in Impala.

Return type: Same as the first argument value

Same as the IS TRUE operator.

Similar to ISNOTFALSE(), except it returns the opposite value for a NULL argument.

Return type: BOOLEAN

Usage notes: Primarily for compatibility with code containing industry extensions to SQL.

Usage notes:

In Impala 2.1.1 and higher, you can use the operators IS [NOT] TRUE and IS [NOT] FALSE as equivalents for the built-in functions ISTRUE(), ISNOTTRUE(), ISFALSE(), and ISNOTFALSE().

Return type: BOOLEAN

Usage notes: Primarily for compatibility with code containing industry extensions to SQL.

Usage notes: This function is effectively shorthand for a CASE expression of the form:

CASE
  WHEN expr1 = expr2 THEN NULL
  ELSE expr1
END

It is commonly used in division expressions, to produce a NULL result instead of a divide-by-zero error when the divisor is equal to zero:

select 1.0 / nullif(c1,0) as reciprocal from t1;

You might also use it for compatibility with other database systems that support the same NULLIF() function.

Return type: same as the initial argument value, except that integer values are promoted to BIGINT and floating-point values are promoted to DOUBLE; use CAST() when inserting into a smaller numeric column

Usage notes: Used to avoid error conditions such as divide-by-zero in numeric calculations. Serves as shorthand for a more elaborate CASE expression, to simplify porting SQL with vendor extensions to Impala.

Return type: Same type as the input argument

Return type: BOOLEAN

Usage notes: Primarily for compatibility with code containing industry extensions to SQL.

Equivalent to the NVL() function in Oracle Database or IFNULL() in MySQL.

Return type: Same as the first argument value

Equivalent to the NVL2() function in Oracle Database.

Return type: Same as the first argument value

Examples:

SELECT NVL2(NULL, 999, 0); -- Returns 0
SELECT NVL2('ABC', 'Is Not Null', 'Is Null'); -- Returns 'Is Not Null'

Usage notes: Used to avoid unexpected results due to unexpected propagation of NULL values in numeric calculations. Serves as shorthand for a more elaborate CASE expression, to simplify porting SQL with vendor extensions to Impala.

Return type: Same type as the input argument