druid/docs/querying/sql-scalar.md

id	title	sidebar_label
sql-scalar	SQL scalar functions	Scalar functions

:::info Apache Druid supports two query languages: Druid SQL and native queries. This document describes the SQL language. :::

Druid SQL includes scalar functions that include numeric and string functions, IP address functions, Sketch functions, and more, as described on this page.

Numeric functions

For mathematical operations, Druid SQL will use integer math if all operands involved in an expression are integers. Otherwise, Druid will switch to floating point math. You can force this to happen by casting one of your operands to FLOAT. At runtime, Druid will widen 32-bit floats to 64-bit for most expressions.

Function	Notes
PI	Constant Pi.
ABS(expr)	Absolute value.
CEIL(expr)	Ceiling.
EXP(expr)	e to the power of expr.
FLOOR(expr)	Floor.
LN(expr)	Logarithm (base e).
LOG10(expr)	Logarithm (base 10).
POWER(expr, power)	expr raised to the power of power.
SQRT(expr)	Square root.
TRUNCATE(expr[, digits])	Truncates expr to a specific number of decimal digits. If digits is negative, then this truncates that many places to the left of the decimal point. If not specified, digits defaults to zero.
TRUNC(expr[, digits])	Alias for TRUNCATE.
ROUND(expr[, digits])	Rounds expr to a specific number of decimal digits. If digits is negative, then it rounds that many places to the left of the decimal point. If not specified, digits defaults to zero.
MOD(x, y)	Modulo (remainder of x divided by y).
SIN(expr)	Trigonometric sine of an angle expr.
COS(expr)	Trigonometric cosine of an angle expr.
TAN(expr)	Trigonometric tangent of an angle expr.
COT(expr)	Trigonometric cotangent of an angle expr.
ASIN(expr)	Arc sine of expr.
ACOS(expr)	Arc cosine of expr.
ATAN(expr)	Arc tangent of expr.
ATAN2(y, x)	Angle theta from the conversion of rectangular coordinates (x, y) to polar * coordinates (r, theta).
DEGREES(expr)	Converts an angle measured in radians to an approximately equivalent angle measured in degrees.
RADIANS(expr)	Converts an angle measured in degrees to an approximately equivalent angle measured in radians.
BITWISE_AND(expr1, expr2)	Returns the result of expr1 & expr2. Double values will be implicitly cast to longs, use BITWISE_CONVERT_DOUBLE_TO_LONG_BITS to perform bitwise operations directly with doubles.
BITWISE_COMPLEMENT(expr)	Returns the result of ~expr. Double values will be implicitly cast to longs, use BITWISE_CONVERT_DOUBLE_TO_LONG_BITS to perform bitwise operations directly with doubles.
BITWISE_CONVERT_DOUBLE_TO_LONG_BITS(expr)	Converts the bits of an IEEE 754 floating-point double value to a long. If the input is not a double, it is implicitly cast to a double prior to conversion.
BITWISE_CONVERT_LONG_BITS_TO_DOUBLE(expr)	Converts a long to the IEEE 754 floating-point double specified by the bits stored in the long. If the input is not a long, it is implicitly cast to a long prior to conversion.
BITWISE_OR(expr1, expr2)	Returns the result of expr1 [PIPE] expr2. Double values will be implicitly cast to longs, use BITWISE_CONVERT_DOUBLE_TO_LONG_BITS to perform bitwise operations directly with doubles.
BITWISE_SHIFT_LEFT(expr1, expr2)	Returns the result of expr1 << expr2. Double values will be implicitly cast to longs, use BITWISE_CONVERT_DOUBLE_TO_LONG_BITS to perform bitwise operations directly with doubles.
BITWISE_SHIFT_RIGHT(expr1, expr2)	Returns the result of expr1 >> expr2. Double values will be implicitly cast to longs, use BITWISE_CONVERT_DOUBLE_TO_LONG_BITS to perform bitwise operations directly with doubles.
BITWISE_XOR(expr1, expr2)	Returns the result of expr1 ^ expr2. Double values will be implicitly cast to longs, use BITWISE_CONVERT_DOUBLE_TO_LONG_BITS to perform bitwise operations directly with doubles.
DIV(x, y)	Returns the result of integer division of x by y
HUMAN_READABLE_BINARY_BYTE_FORMAT(value[, precision])	Formats a number in human-readable IEC format. For example, HUMAN_READABLE_BINARY_BYTE_FORMAT(1048576) returns 1.00 MiB. precision must be in the range of [0, 3]. If not specified, precision defaults to 2.
HUMAN_READABLE_DECIMAL_BYTE_FORMAT(value[, precision])	Formats a number in human-readable SI format. For example, HUMAN_READABLE_DECIMAL_BYTE_FORMAT(1048576) returns 1.04 MB. precision must be in the range of [0, 3]. If not specified, precision defaults to 2.
HUMAN_READABLE_DECIMAL_FORMAT(value[, precision])	Formats a number in human-readable SI format. For example, HUMAN_READABLE_DECIMAL_FORMAT(1048576) returns 1.04 M. precision must be in the range of [0, 3]. If not specified, precision defaults to 2.
SAFE_DIVIDE(x, y)	Returns the division of x by y guarded on division by 0. In case y is 0 it returns 0, or null if druid.generic.useDefaultValueForNull=false

String functions

String functions accept strings and return a type appropriate to the function.

Function	Notes
CONCAT(expr[, expr, ...])	Concatenates a list of expressions. Also see the concatenation operator.
TEXTCAT(expr, expr)	Concatenates two expressions.
CONTAINS_STRING(expr, str)	Returns true if the str is a substring of expr.
ICONTAINS_STRING(expr, str)	Returns true if the str is a substring of expr. The match is case-insensitive.
DECODE_BASE64_UTF8(expr)	Decodes a Base64-encoded string into a UTF-8 encoded string.
LEFT(expr, N)	Returns the N leftmost characters from expr, where N is an integer.
RIGHT(expr, N)	Returns the N rightmost characters from expr, where N is an integer.
LENGTH(expr)	Length of expr in UTF-16 code units.
CHAR_LENGTH(expr)	Alias for LENGTH.
CHARACTER_LENGTH(expr)	Alias for LENGTH.
STRLEN(expr)	Alias for LENGTH.
LOOKUP(expr, lookupName[, replaceMissingValueWith])	Looks up expr in an existing query-time lookup table that has the name lookupName. Returns the optional constant replaceMissingValueWith when expr is null or when the lookup does not contain a value for expr. You can query lookups directly using the lookup schema.
LOWER(expr)	Returns expr in all lowercase.
UPPER(expr)	Returns expr in all uppercase.
LPAD(expr, length[, chars])	Returns a string of length from expr. If expr is shorter than length, left pads expr with chars, which defaults to space characters. If expr exceeds length, truncates expr to equal length. If chars is an empty string, no padding is added. Returns null if either expr or chars is null.
RPAD(expr, length[, chars])	Returns a string of length from expr. If expr is shorter than length, right pads expr with chars, which defaults to space characters. If expr exceeds length, truncates expr to equal length. If chars is an empty string, no padding is added. Returns null if either expr or chars is null.
PARSE_LONG(string[, radix])	Parses a string into a long (BIGINT) with the given radix, or 10 (decimal) if a radix is not provided.
POSITION(substring IN expr [FROM startingIndex])	Returns the index of substring within expr with indexes starting from 1. The search begins at startingIndex. If startingIndex is not specified, the default is 1. If substring is not found, returns 0.
REGEXP_EXTRACT(expr, pattern[, index])	Apply regular expression pattern to expr and extract a capture group or NULL if there is no match. If index is unspecified or zero, returns the first substring that matches the pattern. The pattern may match anywhere inside expr. To match the entire string, use the ^ and $ markers at the start and end of your pattern. When druid.generic.useDefaultValueForNull = true, it is not possible to differentiate an empty-string match from a non-match (both return NULL).
REGEXP_LIKE(expr, pattern)	Returns whether expr matches regular expression pattern. The pattern may match anywhere inside expr; if you want to match the entire string instead, use the ^ and $ markers at the start and end of your pattern. Similar to LIKE, but uses regexps instead of LIKE patterns. Especially useful in WHERE clauses.
REGEXP_REPLACE(expr, pattern, replacement)	Replaces all occurrences of regular expression pattern within expr with replacement. The replacement string may refer to capture groups using $1, $2, etc. The pattern may match anywhere inside expr; if you want to match the entire string instead, use the ^ and $ markers at the start and end of your pattern.
REPLACE(expr, substring, replacement)	Replaces instances of substring in expr with replacement and returns the result.
REPEAT(expr, N)	Repeats expr N times.
REVERSE(expr)	Reverses expr.
STRING_FORMAT(pattern[, args...])	Returns a string formatted in the manner of Java's String.format.
STRPOS(expr, substring)	Returns the index of substring within expr, with indexes starting from 1. If substring is not found, returns 0.
SUBSTRING(expr, index[, length])	Returns a substring of expr starting at a given one-based index. If length is omitted, extracts characters to the end of the string, otherwise returns a substring of length UTF-16 characters.
SUBSTR(expr, index[, length])	Alias for SUBSTRING.
TRIM([BOTH |LEADING| TRAILING] [chars FROM] expr)	Returns expr with characters removed from the leading, trailing, or both ends of expr if they are in chars. If chars is not provided, it defaults to '' (a space). If the directional argument is not provided, it defaults to BOTH.
BTRIM(expr[, chars])	Alternate form of TRIM(BOTH chars FROM expr).
LTRIM(expr[, chars])	Alternate form of TRIM(LEADING chars FROM expr).
RTRIM(expr[, chars])	Alternate form of TRIM(TRAILING chars FROM expr).

Date and time functions

Time functions can be used with:

• Druid's primary timestamp column, __time;
• Numeric values representing milliseconds since the epoch, through the MILLIS_TO_TIMESTAMP function; and
• String timestamps, through the TIME_PARSE function.

By default, time operations use the UTC time zone. You can change the time zone by setting the connection context parameter sqlTimeZone to the name of another time zone, like America/Los_Angeles, or to an offset like -08:00. If you need to mix multiple time zones in the same query, or if you need to use a time zone other than the connection time zone, some functions also accept time zones as parameters. These parameters always take precedence over the connection time zone.

Literal timestamps in the connection time zone can be written using TIMESTAMP '2000-01-01 00:00:00' syntax. The simplest way to write literal timestamps in other time zones is to use TIME_PARSE, like TIME_PARSE('2000-02-01 00:00:00', NULL, 'America/Los_Angeles').

The best ways to filter based on time are by using ISO8601 intervals, like TIME_IN_INTERVAL(__time, '2000-01-01/2000-02-01'), or by using literal timestamps with the >= and < operators, like __time >= TIMESTAMP '2000-01-01 00:00:00' AND __time < TIMESTAMP '2000-02-01 00:00:00'.

Druid supports the standard SQL BETWEEN operator, but we recommend avoiding it for time filters. BETWEEN is inclusive of its upper bound, which makes it awkward to write time filters correctly. For example, the equivalent of TIME_IN_INTERVAL(__time, '2000-01-01/2000-02-01') is __time BETWEEN TIMESTAMP '2000-01-01 00:00:00' AND TIMESTAMP '2000-01-31 23:59:59.999'.

Druid processes timestamps internally as longs (64-bit integers) representing milliseconds since the epoch. Therefore, time functions perform best when used with the primary timestamp column, or with timestamps stored in long columns as milliseconds and accessed with MILLIS_TO_TIMESTAMP. Other timestamp representations, include string timestamps and POSIX timestamps (seconds since the epoch) require query-time conversion to Druid's internal form, which adds additional overhead.

Function	Notes
CURRENT_TIMESTAMP	Current timestamp in the connection's time zone.
CURRENT_DATE	Current date in the connection's time zone.
DATE_TRUNC(unit, timestamp_expr)	Rounds down a timestamp, returning it as a new timestamp. Unit can be 'milliseconds', 'second', 'minute', 'hour', 'day', 'week', 'month', 'quarter', 'year', 'decade', 'century', or 'millennium'.
TIME_CEIL(timestamp_expr, period[, origin[, timezone]])	Rounds up a timestamp, returning it as a new timestamp. Period can be any ISO8601 period, like P3M (quarters) or PT12H (half-days). Specify origin as a timestamp to set the reference time for rounding. For example, TIME_CEIL(__time, 'PT1H', TIMESTAMP '2016-06-27 00:30:00') measures an hourly period from 00:30-01:30 instead of 00:00-01:00. See Period granularities for details on the default starting boundaries. The time zone, if provided, should be a time zone name like "America/Los_Angeles" or offset like "-08:00". This function is similar to CEIL but is more flexible.
TIME_FLOOR(timestamp_expr, period[, origin[, timezone]])	Rounds down a timestamp, returning it as a new timestamp. Period can be any ISO8601 period, like P3M (quarters) or PT12H (half-days). Specify origin as a timestamp to set the reference time for rounding. For example, TIME_FLOOR(__time, 'PT1H', TIMESTAMP '2016-06-27 00:30:00') measures an hourly period from 00:30-01:30 instead of 00:00-01:00. See Period granularities for details on the default starting boundaries. The time zone, if provided, should be a time zone name like "America/Los_Angeles" or offset like "-08:00". This function is similar to FLOOR but is more flexible.
TIME_SHIFT(timestamp_expr, period, step[, timezone])	Shifts a timestamp by a period (step times), returning it as a new timestamp. Period can be any ISO8601 period. Step may be negative. The time zone, if provided, should be a time zone name like "America/Los_Angeles" or offset like "-08:00".
TIME_EXTRACT(timestamp_expr[, unit[, timezone]])	Extracts a time part from expr, returning it as a number. Unit can be EPOCH, SECOND, MINUTE, HOUR, DAY (day of month), DOW (day of week), DOY (day of year), WEEK (week of week year), MONTH (1 through 12), QUARTER (1 through 4), or YEAR. The time zone, if provided, should be a time zone name like "America/Los_Angeles" or offset like "-08:00". This function is similar to EXTRACT but is more flexible. Unit and time zone must be literals, and must be provided quoted, like TIME_EXTRACT(__time, 'HOUR') or TIME_EXTRACT(__time, 'HOUR', 'America/Los_Angeles').
TIME_PARSE(string_expr[, pattern[, timezone]])	Parses a string into a timestamp using a given Joda DateTimeFormat pattern, or ISO8601 (e.g. 2000-01-02T03:04:05Z) if the pattern is not provided. The time zone, if provided, should be a time zone name like "America/Los_Angeles" or offset like "-08:00", and will be used as the time zone for strings that do not include a time zone offset. Pattern and time zone must be literals. Strings that cannot be parsed as timestamps will be returned as NULL.
TIME_FORMAT(timestamp_expr[, pattern[, timezone]])	Formats a timestamp as a string with a given Joda DateTimeFormat pattern, or ISO8601 (e.g. 2000-01-02T03:04:05Z) if the pattern is not provided. The time zone, if provided, should be a time zone name like "America/Los_Angeles" or offset like "-08:00". Pattern and time zone must be literals.
TIME_IN_INTERVAL(timestamp_expr, interval)	Returns whether a timestamp is contained within a particular interval. The interval must be a literal string containing any ISO8601 interval, such as '2001-01-01/P1D' or '2001-01-01T01:00:00/2001-01-02T01:00:00'. The start instant of the interval is inclusive and the end instant is exclusive.
MILLIS_TO_TIMESTAMP(millis_expr)	Converts a number of milliseconds since the epoch (1970-01-01 00:00:00 UTC) into a timestamp.
TIMESTAMP_TO_MILLIS(timestamp_expr)	Converts a timestamp into a number of milliseconds since the epoch.
EXTRACT(unit FROM timestamp_expr)	Extracts a time part from expr, returning it as a number. Unit can be EPOCH, MICROSECOND, MILLISECOND, SECOND, MINUTE, HOUR, DAY (day of month), DOW (day of week), ISODOW (ISO day of week), DOY (day of year), WEEK (week of year), MONTH, QUARTER, YEAR, ISOYEAR, DECADE, CENTURY or MILLENNIUM. Units must be provided unquoted, like EXTRACT(HOUR FROM __time).
FLOOR(timestamp_expr TO unit)	Rounds down a timestamp, returning it as a new timestamp. Unit can be SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.
CEIL(timestamp_expr TO unit)	Rounds up a timestamp, returning it as a new timestamp. Unit can be SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.
TIMESTAMPADD(unit, count, timestamp)	Equivalent to timestamp + count * INTERVAL '1' UNIT.
TIMESTAMPDIFF(unit, timestamp1, timestamp2)	Returns the (signed) number of unit between timestamp1 and timestamp2. Unit can be SECOND, MINUTE, HOUR, DAY, WEEK, MONTH, QUARTER, or YEAR.

Reduction functions

Reduction functions operate on zero or more expressions and return a single expression. If no expressions are passed as arguments, then the result is NULL. The expressions must all be convertible to a common data type, which will be the type of the result:

• If all argument are NULL, the result is NULL. Otherwise, NULL arguments are ignored.
• If the arguments comprise a mix of numbers and strings, the arguments are interpreted as strings.
• If all arguments are integer numbers, the arguments are interpreted as longs.
• If all arguments are numbers and at least one argument is a double, the arguments are interpreted as doubles.

Function	Notes
GREATEST([expr1, ...])	Evaluates zero or more expressions and returns the maximum value based on comparisons as described above.
LEAST([expr1, ...])	Evaluates zero or more expressions and returns the minimum value based on comparisons as described above.

IP address functions

For the IPv4 address functions, the address argument can either be an IPv4 dotted-decimal string (e.g., "192.168.0.1") or an IP address represented as an integer (e.g., 3232235521). The subnet argument should be a string formatted as an IPv4 address subnet in CIDR notation (e.g., "192.168.0.0/16").

For the IPv6 address function, the address argument accepts a semicolon separated string (e.g. "75e9:efa4:29c6:85f6::232c"). The format of the subnet argument should be an IPv6 address subnet in CIDR notation (e.g. "75e9:efa4:29c6:85f6::/64").

Function	Notes
IPV4_MATCH(address, subnet)	Returns true if the address belongs to the subnet literal, else false. If address is not a valid IPv4 address, then false is returned. This function is more efficient if address is an integer instead of a string.
IPV4_PARSE(address)	Parses address into an IPv4 address stored as an integer . If address is an integer that is a valid IPv4 address, then it is passed through. Returns null if address cannot be represented as an IPv4 address.
IPV4_STRINGIFY(address)	Converts address into an IPv4 address dotted-decimal string. If address is a string that is a valid IPv4 address, then it is passed through. Returns null if address cannot be represented as an IPv4 address.
IPV6_MATCH(address, subnet)	Returns 1 if the IPv6 address belongs to the subnet literal, else 0. If address is not a valid IPv6 address, then 0 is returned.

Sketch functions

These functions operate on expressions or columns that return sketch objects. To create sketch objects, see the DataSketches aggregators.

HLL sketch functions

The following functions operate on DataSketches HLL sketches. The DataSketches extension must be loaded to use the following functions.

Function	Notes
HLL_SKETCH_ESTIMATE(expr[, round])	Returns the distinct count estimate from an HLL sketch. expr must return an HLL sketch. The optional round boolean parameter will round the estimate if set to true, with a default of false.
HLL_SKETCH_ESTIMATE_WITH_ERROR_BOUNDS(expr[, numStdDev])	Returns the distinct count estimate and error bounds from an HLL sketch. expr must return an HLL sketch. An optional numStdDev argument can be provided.
HLL_SKETCH_UNION([lgK, tgtHllType], expr0, expr1, ...)	Returns a union of HLL sketches, where each input expression must return an HLL sketch. The lgK and tgtHllType can be optionally specified as the first parameter; if provided, both optional parameters must be specified.
HLL_SKETCH_TO_STRING(expr)	Returns a human-readable string representation of an HLL sketch for debugging. expr must return an HLL sketch.

Theta sketch functions

The following functions operate on theta sketches. The DataSketches extension must be loaded to use the following functions.

Function	Notes
THETA_SKETCH_ESTIMATE(expr)	Returns the distinct count estimate from a theta sketch. expr must return a theta sketch.
THETA_SKETCH_ESTIMATE_WITH_ERROR_BOUNDS(expr, errorBoundsStdDev)	Returns the distinct count estimate and error bounds from a theta sketch. expr must return a theta sketch.
THETA_SKETCH_UNION([size], expr0, expr1, ...)	Returns a union of theta sketches, where each input expression must return a theta sketch. The size can be optionally specified as the first parameter.
THETA_SKETCH_INTERSECT([size], expr0, expr1, ...)	Returns an intersection of theta sketches, where each input expression must return a theta sketch. The size can be optionally specified as the first parameter.
THETA_SKETCH_NOT([size], expr0, expr1, ...)	Returns a set difference of theta sketches, where each input expression must return a theta sketch. The size can be optionally specified as the first parameter.

Quantiles sketch functions

The following functions operate on quantiles sketches. The DataSketches extension must be loaded to use the following functions.

Function	Notes
DS_GET_QUANTILE(expr, fraction)	Returns the quantile estimate corresponding to fraction from a quantiles sketch. expr must return a quantiles sketch.
DS_GET_QUANTILES(expr, fraction0, fraction1, ...)	Returns a string representing an array of quantile estimates corresponding to a list of fractions from a quantiles sketch. expr must return a quantiles sketch.
DS_HISTOGRAM(expr, splitPoint0, splitPoint1, ...)	Returns a string representing an approximation to the histogram given a list of split points that define the histogram bins from a quantiles sketch. expr must return a quantiles sketch.
DS_CDF(expr, splitPoint0, splitPoint1, ...)	Returns a string representing approximation to the Cumulative Distribution Function given a list of split points that define the edges of the bins from a quantiles sketch. expr must return a quantiles sketch.
DS_RANK(expr, value)	Returns an approximation to the rank of a given value that is the fraction of the distribution less than that value from a quantiles sketch. expr must return a quantiles sketch.
DS_QUANTILE_SUMMARY(expr)	Returns a string summary of a quantiles sketch, useful for debugging. expr must return a quantiles sketch.

Tuple sketch functions

The following functions operate on tuple sketches. The DataSketches extension must be loaded to use the following functions.

Function	Notes	Default
DS_TUPLE_DOUBLES_METRICS_SUM_ESTIMATE(expr)	Computes approximate sums of the values contained within a Tuple sketch column which contains an array of double values as its Summary Object.
DS_TUPLE_DOUBLES_INTERSECT(expr, ...[, nominalEntries])	Returns an intersection of tuple sketches, where each input expression must return a tuple sketch which contains an array of double values as its Summary Object. The values contained in the Summary Objects are summed when combined. If the last value of the array is a numeric literal, Druid assumes that the value is an override parameter for nominal entries.
DS_TUPLE_DOUBLES_NOT(expr, ...[, nominalEntries])	Returns a set difference of tuple sketches, where each input expression must return a tuple sketch which contains an array of double values as its Summary Object. The values contained in the Summary Object are preserved as is. If the last value of the array is a numeric literal, Druid assumes that the value is an override parameter for nominal entries.
DS_TUPLE_DOUBLES_UNION(expr, ...[, nominalEntries])	Returns a union of tuple sketches, where each input expression must return a tuple sketch which contains an array of double values as its Summary Object. The values contained in the Summary Objects are summed when combined. If the last value of the array is a numeric literal, Druid assumes that the value is an override parameter for nominal entries.

Other scalar functions

Function	Notes
BLOOM_FILTER_TEST(expr, serialized-filter)	Returns true if the value of expr is contained in the base64-serialized Bloom filter. See the Bloom filter extension documentation for additional details. See the BLOOM_FILTER function for computing Bloom filters.
CASE expr WHEN value1 THEN result1 \[ WHEN value2 THEN result2 ... \] \[ ELSE resultN \] END	Simple CASE.
CASE WHEN boolean_expr1 THEN result1 \[ WHEN boolean_expr2 THEN result2 ... \] \[ ELSE resultN \] END	Searched CASE.
CAST(value AS TYPE)	Cast value to another type. See Data types for details about how Druid SQL handles CAST.
COALESCE(value1, value2, ...)	Returns the first value that is neither NULL nor empty string.
DECODE_BASE64_COMPLEX(dataType, expr)	Decodes a Base64-encoded string into a complex data type, where dataType is the complex data type and expr is the Base64-encoded string to decode. The hyperUnique and serializablePairLongString data types are supported by default. You can enable support for the following complex data types by loading their extensions: druid-bloom-filter: bloom druid-datasketches: arrayOfDoublesSketch, HLLSketch, KllDoublesSketch, KllFloatsSketch, quantilesDoublesSketch, thetaSketch druid-histogram: approximateHistogram, fixedBucketsHistogram druid-stats: variance druid-compressed-bigdecimal: compressedBigDecimal druid-momentsketch: momentSketch druid-tdigestsketch: tDigestSketch
NULLIF(value1, value2)	Returns NULL if value1 and value2 match, else returns value1.
NVL(value1, value2)	Returns value1 if value1 is not null, otherwise value2.