Druid SQL supports dynamic parameters in question mark (`?`) syntax, where parameters are bound to the `?` placeholders at execution time. To use dynamic parameters, replace any literal in the query with a `?` character and ensure that corresponding parameter values are provided at execution time. Parameters are bound to the placeholders in the order in which they are passed.
If `druid.generic.useDefaultValueForNull` is set to `false`_system-wide, at indexing time_, data
will be stored in a manner that allows distinguishing empty strings from NULL values for string columns, and will allow NULL values to be stored for numeric columns. Druid SQL will generally operate more properly and the SQL optimizer will work best in this mode, however this does come at a cost. See the [segment documentation on SQL compatible null-handling](../design/segments.md#sql-compatible-null-handling) for more details.
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 may widen 32-bit floats to 64-bit for certain operators, like SUM aggregators.
Druid [multi-value string dimensions](multi-value-dimensions.html) will appear in the table schema as `VARCHAR` typed,
and may be interacted with in expressions as such. Additionally, they can be treated as `ARRAY` 'like', via a handful of
special multi-value operators. Expressions against multi-value string dimensions will apply the expression to all values
of the row, however the caveat is that aggregations on these multi-value string columns will observe the native Druid
multi-value aggregation behavior, which is equivalent to the `UNNEST` function available in many dialects.
Refer to the documentation on [multi-value string dimensions](multi-value-dimensions.html) and
[Druid expressions documentation](../misc/math-expr.html) for additional details.
The following table describes how SQL types map onto Druid types during query runtime. Casts between two SQL types
that have the same Druid runtime type will have no effect, other than exceptions noted in the table. Casts between two
SQL types that have different Druid runtime types will generate a runtime cast in Druid. If a value cannot be properly
cast to another value, as in `CAST('foo' AS BIGINT)`, the runtime will substitute a default value. NULL values cast
to non-nullable types will also be substituted with a default value (for example, nulls cast to numbers will be
converted to zeroes).
|SQL type|Druid runtime type|Default value|Notes|
|--------|------------------|-------------|-----|
|CHAR|STRING|`''`||
|VARCHAR|STRING|`''`|Druid STRING columns are reported as VARCHAR|
|DECIMAL|DOUBLE|`0.0`|DECIMAL uses floating point, not fixed point math|
|FLOAT|FLOAT|`0.0`|Druid FLOAT columns are reported as FLOAT|
|REAL|DOUBLE|`0.0`||
|DOUBLE|DOUBLE|`0.0`|Druid DOUBLE columns are reported as DOUBLE|
|BOOLEAN|LONG|`false`||
|TINYINT|LONG|`0`||
|SMALLINT|LONG|`0`||
|INTEGER|LONG|`0`||
|BIGINT|LONG|`0`|Druid LONG columns (except `__time`) are reported as BIGINT|
|TIMESTAMP|LONG|`0`, meaning 1970-01-01 00:00:00 UTC|Druid's `__time` column is reported as TIMESTAMP. Casts between string and timestamp types assume standard SQL formatting, e.g. `2000-01-02 03:04:05`, _not_ ISO8601 formatting. For handling other formats, use one of the [time functions](#time-functions)|
|DATE|LONG|`0`, meaning 1970-01-01|Casting TIMESTAMP to DATE rounds down the timestamp to the nearest day. Casts between string and date types assume standard SQL formatting, e.g. `2000-01-02`. For handling other formats, use one of the [time functions](#time-functions)|
|OTHER|COMPLEX|none|May represent various Druid column types such as hyperUnique, approxHistogram, etc|
Aggregation functions can appear in the SELECT clause of any query. Any aggregator can be filtered using syntax like
`AGG(expr) FILTER(WHERE whereExpr)`. Filtered aggregators will only aggregate rows that match their filter. It's
possible for two aggregators in the same SQL query to have different filters.
Only the COUNT aggregation can accept DISTINCT.
|Function|Notes|
|--------|-----|
|`COUNT(*)`|Counts the number of rows.|
|`COUNT(DISTINCT expr)`|Counts distinct values of expr, which can be string, numeric, or hyperUnique. By default this is approximate, using a variant of [HyperLogLog](http://algo.inria.fr/flajolet/Publications/FlFuGaMe07.pdf). To get exact counts set "useApproximateCountDistinct" to "false". If you do this, expr must be string or numeric, since exact counts are not possible using hyperUnique columns. See also `APPROX_COUNT_DISTINCT(expr)`. In exact mode, only one distinct count per query is permitted.|
|`APPROX_COUNT_DISTINCT(expr)`|Counts distinct values of expr, which can be a regular column or a hyperUnique column. This is always approximate, regardless of the value of "useApproximateCountDistinct". This uses Druid's built-in "cardinality" or "hyperUnique" aggregators. See also `COUNT(DISTINCT expr)`.|
|`APPROX_COUNT_DISTINCT_DS_HLL(expr, [lgK, tgtHllType])`|Counts distinct values of expr, which can be a regular column or an [HLL sketch](../development/extensions-core/datasketches-hll.html) column. The `lgK` and `tgtHllType` parameters are described in the HLL sketch documentation. This is always approximate, regardless of the value of "useApproximateCountDistinct". See also `COUNT(DISTINCT expr)`. The [DataSketches extension](../development/extensions-core/datasketches-extension.html) must be loaded to use this function.|
|`APPROX_COUNT_DISTINCT_DS_THETA(expr, [size])`|Counts distinct values of expr, which can be a regular column or a [Theta sketch](../development/extensions-core/datasketches-theta.html) column. The `size` parameter is described in the Theta sketch documentation. This is always approximate, regardless of the value of "useApproximateCountDistinct". See also `COUNT(DISTINCT expr)`. The [DataSketches extension](../development/extensions-core/datasketches-extension.html) must be loaded to use this function.|
|`DS_HLL(expr, [lgK, tgtHllType])`|Creates an [HLL sketch](../development/extensions-core/datasketches-hll.html) on the values of expr, which can be a regular column or a column containing HLL sketches. The `lgK` and `tgtHllType` parameters are described in the HLL sketch documentation. The [DataSketches extension](../development/extensions-core/datasketches-extension.html) must be loaded to use this function.|
|`DS_THETA(expr, [size])`|Creates a [Theta sketch](../development/extensions-core/datasketches-theta.html) on the values of expr, which can be a regular column or a column containing Theta sketches. The `size` parameter is described in the Theta sketch documentation. The [DataSketches extension](../development/extensions-core/datasketches-extension.html) must be loaded to use this function.|
|`APPROX_QUANTILE(expr, probability, [resolution])`|Computes approximate quantiles on numeric or [approxHistogram](../development/extensions-core/approximate-histograms.html#approximate-histogram-aggregator) exprs. The "probability" should be between 0 and 1 (exclusive). The "resolution" is the number of centroids to use for the computation. Higher resolutions will give more precise results but also have higher overhead. If not provided, the default resolution is 50. The [approximate histogram extension](../development/extensions-core/approximate-histograms.html) must be loaded to use this function.|
|`APPROX_QUANTILE_DS(expr, probability, [k])`|Computes approximate quantiles on numeric or [Quantiles sketch](../development/extensions-core/datasketches-quantiles.html) exprs. The "probability" should be between 0 and 1 (exclusive). The `k` parameter is described in the Quantiles sketch documentation. The [DataSketches extension](../development/extensions-core/datasketches-extension.html) must be loaded to use this function.|
|`APPROX_QUANTILE_FIXED_BUCKETS(expr, probability, numBuckets, lowerLimit, upperLimit, [outlierHandlingMode])`|Computes approximate quantiles on numeric or [fixed buckets histogram](../development/extensions-core/approximate-histograms.html#fixed-buckets-histogram) exprs. The "probability" should be between 0 and 1 (exclusive). The `numBuckets`, `lowerLimit`, `upperLimit`, and `outlierHandlingMode` parameters are described in the fixed buckets histogram documentation. The [approximate histogram extension](../development/extensions-core/approximate-histograms.html) must be loaded to use this function.|
|`DS_QUANTILES_SKETCH(expr, [k])`|Creates a [Quantiles sketch](../development/extensions-core/datasketches-quantiles.html) on the values of expr, which can be a regular column or a column containing quantiles sketches. The `k` parameter is described in the Quantiles sketch documentation. The [DataSketches extension](../development/extensions-core/datasketches-extension.html) must be loaded to use this function.|
|`BLOOM_FILTER(expr, numEntries)`|Computes a bloom filter from values produced by `expr`, with `numEntries` maximum number of distinct values before false positive rate increases. See [bloom filter extension](../development/extensions-core/bloom-filter.html) documentation for additional details.|
|`TDIGEST_QUANTILE(expr, quantileFraction, [compression])`|Builds a T-Digest sketch on values produced by `expr` and returns the value for the quantile. Compression parameter (default value 100) determines the accuracy and size of the sketch. Higher compression means higher accuracy but more space to store sketches. See [t-digest extension](../development/extensions-contrib/tdigestsketch-quantiles.html) documentation for additional details.|
|`TDIGEST_GENERATE_SKETCH(expr, [compression])`|Builds a T-Digest sketch on values produced by `expr`. Compression parameter (default value 100) determines the accuracy and size of the sketch Higher compression means higher accuracy but more space to store sketches. See [t-digest extension](../development/extensions-contrib/tdigestsketch-quantiles.html) documentation for additional details.|
|`VAR_POP(expr)`|Computes variance population of `expr`. See [stats extension](../development/extensions-core/stats.html) documentation for additional details.|
|`VAR_SAMP(expr)`|Computes variance sample of `expr`. See [stats extension](../development/extensions-core/stats.html) documentation for additional details.|
|`VARIANCE(expr)`|Computes variance sample of `expr`. See [stats extension](../development/extensions-core/stats.html) documentation for additional details.|
|`STDDEV_POP(expr)`|Computes standard deviation population of `expr`. See [stats extension](../development/extensions-core/stats.html) documentation for additional details.|
|`STDDEV_SAMP(expr)`|Computes standard deviation sample of `expr`. See [stats extension](../development/extensions-core/stats.html) documentation for additional details.|
|`STDDEV(expr)`|Computes standard deviation sample of `expr`. See [stats extension](../development/extensions-core/stats.html) documentation for additional details.|
|`EARLIEST(expr)`|Returns the earliest value of `expr`, which must be numeric. If `expr` comes from a relation with a timestamp column (like a Druid datasource) then "earliest" is the value first encountered with the minimum overall timestamp of all values being aggregated. If `expr` does not come from a relation with a timestamp, then it is simply the first value encountered.|
|`EARLIEST(expr, maxBytesPerString)`|Like `EARLIEST(expr)`, but for strings. The `maxBytesPerString` parameter determines how much aggregation space to allocate per string. Strings longer than this limit will be truncated. This parameter should be set as low as possible, since high values will lead to wasted memory.|
|`LATEST(expr)`|Returns the latest value of `expr`, which must be numeric. If `expr` comes from a relation with a timestamp column (like a Druid datasource) then "latest" is the value last encountered with the maximum overall timestamp of all values being aggregated. If `expr` does not come from a relation with a timestamp, then it is simply the last value encountered.|
|`LATEST(expr, maxBytesPerString)`|Like `LATEST(expr)`, but for strings. The `maxBytesPerString` parameter determines how much aggregation space to allocate per string. Strings longer than this limit will be truncated. This parameter should be set as low as possible, since high values will lead to wasted memory.|
|`ANY_VALUE(expr)`|Returns any value of `expr` including null. `expr` must be numeric. This aggregator can simplify and optimize the performance by returning the first encountered value (including null)|
|`ANY_VALUE(expr, maxBytesPerString)`|Like `ANY_VALUE(expr)`, but for strings. The `maxBytesPerString` parameter determines how much aggregation space to allocate per string. Strings longer than this limit will be truncated. This parameter should be set as low as possible, since high values will lead to wasted memory.|
|`TRUNCATE(expr[, digits])`|Truncate 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. Digits defaults to zero if not specified.|
|`ROUND(expr[, digits])`|`ROUND(x, y)` would return the value of the x rounded to the y decimal places. While x can be an integer or floating-point number, y must be an integer. The type of the return value is specified by that of x. y defaults to 0 if omitted. When y is negative, x is rounded on the left side of the y decimal points.|
|`STRING_FORMAT(pattern[, args...])`|Returns a string formatted in the manner of Java's [String.format](https://docs.oracle.com/javase/8/docs/api/java/lang/String.html#format-java.lang.String-java.lang.Object...-).|
|`POSITION(needle IN haystack [FROM fromIndex])`|Returns the index of needle within haystack, with indexes starting from 1. The search will begin at fromIndex, or 1 if fromIndex is not specified. If the needle is not found, returns 0.|
|`REGEXP_EXTRACT(expr, pattern, [index])`|Apply regular expression pattern and extract a capture group, or null if there is no match. If index is unspecified or zero, returns the substring that matched the pattern.|
|`REPLACE(expr, pattern, replacement)`|Replaces pattern with replacement in expr, and returns the result.|
|<code>TRIM([BOTH | LEADING | TRAILING] [<chars> FROM] expr)</code>|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".|
|`LPAD(expr, length[, chars])`|Returns a string of "length" from "expr" left-padded with "chars". If "length" is shorter than the length of "expr", the result is "expr" which is truncated to "length". If either "expr" or "chars" are null, the result will be null.|
|`RPAD(expr, length[, chars])`|Returns a string of "length" from "expr" right-padded with "chars". If "length" is shorter than the length of "expr", the result is "expr" which is truncated to "length". If either "expr" or "chars" are null, the result will be null.|
|`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). 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). 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](https://en.wikipedia.org/wiki/ISO_week_date)), 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](http://www.joda.org/joda-time/apidocs/org/joda/time/format/DateTimeFormat.html), 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](http://www.joda.org/joda-time/apidocs/org/joda/time/format/DateTimeFormat.html), 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.|
|`MILLIS_TO_TIMESTAMP(millis_expr)`|Converts a number of milliseconds since the epoch 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.|
|`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.|
|<code>timestamp_expr { + | - } <interval_expr><code>|Add or subtract an amount of time from a timestamp. interval_expr can include interval literals like `INTERVAL '2' HOUR`, and may include interval arithmetic as well. This operator treats days as uniformly 86400 seconds long, and does not take into account daylight savings time. To account for daylight savings time, use TIME_SHIFT instead.|
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').
|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.|
|`x IN (subquery)`|True if x is returned by the subquery. See [Query execution](#query-execution) above for details about how Druid SQL handles `IN (subquery)`.|
|`x NOT IN (subquery)`|True if x is not returned by the subquery. See [Query execution](#query-execution) for details about how Druid SQL handles `IN (subquery)`.|
| `ARRAY(expr1,expr ...)` | constructs a SQL ARRAY literal from the expression arguments, using the type of the first argument as the output array type |
| `MV_LENGTH(arr)` | returns length of array expression |
| `MV_OFFSET(arr,long)` | returns the array element at the 0 based index supplied, or null for an out of range index|
| `MV_ORDINAL(arr,long)` | returns the array element at the 1 based index supplied, or null for an out of range index |
| `MV_CONTAINS(arr,expr)` | returns 1 if the array contains the element specified by expr, or contains all elements specified by expr if expr is an array, else 0 |
| `MV_OVERLAP(arr1,arr2)` | returns 1 if arr1 and arr2 have any elements in common, else 0 |
| `MV_OFFSET_OF(arr,expr)` | returns the 0 based index of the first occurrence of expr in the array, or `-1` or `null` if `druid.generic.useDefaultValueForNull=false` if no matching elements exist in the array. |
| `MV_ORDINAL_OF(arr,expr)` | returns the 1 based index of the first occurrence of expr in the array, or `-1` or `null` if `druid.generic.useDefaultValueForNull=false` if no matching elements exist in the array. |
| `MV_PREPEND(expr,arr)` | adds expr to arr at the beginning, the resulting array type determined by the type of the array |
| `MV_APPEND(arr1,expr)` | appends expr to arr, the resulting array type determined by the type of the first array |
| `MV_CONCAT(arr1,arr2)` | concatenates 2 arrays, the resulting array type determined by the type of the first array |
| `MV_SLICE(arr,start,end)` | return the subarray of arr from the 0 based index start(inclusive) to end(exclusive), or `null`, if start is less than 0, greater than length of arr or less than end|
| `MV_TO_STRING(arr,str)` | joins all elements of arr by the delimiter specified by str |
| `STRING_TO_MV(str1,str2)` | splits str1 into an array on the delimiter specified by str2 |
These functions operate on expressions or columns that return sketch objects.
#### HLL sketch operators
The following functions operate on [DataSketches HLL sketches](../development/extensions-core/datasketches-hll.html).
The [DataSketches extension](../development/extensions-core/datasketches-extension.html) 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 operators
The following functions operate on [theta sketches](../development/extensions-core/datasketches-theta.html).
The [DataSketches extension](../development/extensions-core/datasketches-extension.html) 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 operators
The following functions operate on [quantiles sketches](../development/extensions-core/datasketches-quantiles.html).
The [DataSketches extension](../development/extensions-core/datasketches-extension.html) 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.|
|`NVL(expr,expr-for-null)`|Returns 'expr-for-null' if 'expr' is null (or empty string for string type).|
|`BLOOM_FILTER_TEST(<expr>, <serialized-filter>)`|Returns true if the value is contained in the base64 serialized bloom filter. See [bloom filter extension](../development/extensions-core/bloom-filter.html) documentation for additional details.|
|`type`|`String` (`SqlType`) | String value of `SqlType` of parameter. [`SqlType`](https://calcite.apache.org/avatica/javadocAggregate/org/apache/calcite/avatica/SqlType.html) is a friendly wrapper around [`java.sql.Types`](https://docs.oracle.com/javase/8/docs/api/java/sql/Types.html?is-external=true)|yes|
|`value`|`Object`| Value of the parameter|yes|
Metadata is also available over the HTTP API by querying [system tables](#metadata-tables).
"query" : "SELECT COUNT(*) FROM data_source WHERE foo = 'bar' AND __time > TIMESTAMP '2000-01-01 00:00:00'",
"resultFormat" : "object"
}
```
The supported result formats are:
|Format|Description|Content-Type|
|------|-----------|------------|
|`object`|The default, a JSON array of JSON objects. Each object's field names match the columns returned by the SQL query, and are provided in the same order as the SQL query.|application/json|
|`array`|JSON array of JSON arrays. Each inner array has elements matching the columns returned by the SQL query, in order.|application/json|
|`objectLines`|Like "object", but the JSON objects are separated by newlines instead of being wrapped in a JSON array. This can make it easier to parse the entire response set as a stream, if you do not have ready access to a streaming JSON parser. To make it possible to detect a truncated response, this format includes a trailer of one blank line.|text/plain|
|`arrayLines`|Like "array", but the JSON arrays are separated by newlines instead of being wrapped in a JSON array. This can make it easier to parse the entire response set as a stream, if you do not have ready access to a streaming JSON parser. To make it possible to detect a truncated response, this format includes a trailer of one blank line.|text/plain|
|`csv`|Comma-separated values, with one row per line. Individual field values may be escaped by being surrounded in double quotes. If double quotes appear in a field value, they will be escaped by replacing them with double-double-quotes like `""this""`. To make it possible to detect a truncated response, this format includes a trailer of one blank line.|text/csv|
|`sqlTimeZone`|Sets the time zone for this connection, which will affect how time functions and timestamp literals behave. Should be a time zone name like "America/Los_Angeles" or offset like "-08:00".|druid.sql.planner.sqlTimeZone on the Broker (default: UTC)|
|`useApproximateCountDistinct`|Whether to use an approximate cardinality algorithm for `COUNT(DISTINCT foo)`.|druid.sql.planner.useApproximateCountDistinct on the Broker (default: true)|
|`useApproximateTopN`|Whether to use approximate [TopN queries](topnquery.html) when a SQL query could be expressed as such. If false, exact [GroupBy queries](groupbyquery.html) will be used instead.|druid.sql.planner.useApproximateTopN on the Broker (default: true)|
Druid exposes system information through special system tables. There are two such schemas available: Information Schema and Sys Schema.
Information schema provides details about table and column types. The "sys" schema provides information about Druid internals like segments/tasks/servers.
|start|STRING|Interval start time (in ISO 8601 format)|
|end|STRING|Interval end time (in ISO 8601 format)|
|size|LONG|Size of segment in bytes|
|version|STRING|Version string (generally an ISO8601 timestamp corresponding to when the segment set was first started). Higher version means the more recently created segment. Version comparing is based on string comparison.|
|partition_num|LONG|Partition number (an integer, unique within a datasource+interval+version; may not necessarily be contiguous)|
|num_replicas|LONG|Number of replicas of this segment currently being served|
|is_published|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 represents this segment has been published to the metadata store with `used=1`. See the [Architecture page](../design/architecture.md#segment-lifecycle) for more details.|
|is_available|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 if this segment is currently being served by any process(Historical or realtime). See the [Architecture page](../design/architecture.md#segment-lifecycle) for more details.|
|is_realtime|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 if this segment is _only_ served by realtime tasks, and 0 if any historical process is serving this segment.|
|is_overshadowed|LONG|Boolean is represented as long type where 1 = true, 0 = false. 1 if this segment is published and is _fully_ overshadowed by some other published segments. Currently, is_overshadowed is always false for unpublished segments, although this may change in the future. You can filter for segments that "should be published" by filtering for `is_published = 1 AND is_overshadowed = 0`. Segments can briefly be both published and overshadowed if they were recently replaced, but have not been unpublished yet. See the [Architecture page](../design/architecture.md#segment-lifecycle) for more details.|
*Caveat:* Note that a segment can be served by more than one stream ingestion tasks or Historical processes, in that case it would have multiple replicas. These replicas are weakly consistent with each other when served by multiple ingestion tasks, until a segment is eventually served by a Historical, at that point the segment is immutable. Broker prefers to query a segment from Historical over an ingestion task. But if a segment has multiple realtime replicas, for e.g.. Kafka index tasks, and one task is slower than other, then the sys.segments query results can vary for the duration of the tasks because only one of the ingestion tasks is queried by the Broker and it is not guaranteed that the same task gets picked every time. The `num_rows` column of segments table can have inconsistent values during this period. There is an open [issue](https://github.com/apache/druid/issues/5915) about this inconsistency with stream ingestion tasks.
|tier|STRING|Distribution tier see [druid.server.tier](../configuration/index.html#historical-general-configuration). Only valid for HISTORICAL type, for other types it's null|
|max_size|LONG|Max size in bytes this server recommends to assign to segments see [druid.server.maxSize](../configuration/index.html#historical-general-configuration). Only valid for HISTORICAL type, for other types it's 0|
|group_id|STRING|Task group ID for this task, the value depends on the task `type`. For example, for native index tasks, it's same as `task_id`, for sub tasks, this value is the parent task's ID|
|type|STRING|Task type, for example this value is "index" for indexing tasks. See [tasks-overview](../ingestion/tasks.html)|
|created_time|STRING|Timestamp in ISO8601 format corresponding to when the ingestion task was created. Note that this value is populated for completed and waiting tasks. For running and pending tasks this value is set to 1970-01-01T00:00:00Z|
|queue_insertion_time|STRING|Timestamp in ISO8601 format corresponding to when this task was added to the queue on the Overlord|
|status|STRING|Status of a task can be RUNNING, FAILED, SUCCESS|
|runner_status|STRING|Runner status of a completed task would be NONE, for in-progress tasks this can be RUNNING, WAITING, PENDING|
|duration|LONG|Time it took to finish the task in milliseconds, this value is present only for completed tasks|
|location|STRING|Server name where this task is running in the format host:port, this information is present only for RUNNING tasks|
|host|STRING|Hostname of the server where task is running|
|plaintext_port|LONG|Unsecured port of the server, or -1 if plaintext traffic is disabled|
|tls_port|LONG|TLS port of the server, or -1 if TLS is disabled|
|error_msg|STRING|Detailed error message in case of FAILED tasks|
The supervisors table provides information about supervisors.
|Column|Type|Notes|
|------|-----|-----|
|supervisor_id|STRING|Supervisor task identifier|
|state|STRING|Basic state of the supervisor. Available states: `UNHEALTHY_SUPERVISOR`, `UNHEALTHY_TASKS`, `PENDING`, `RUNNING`, `SUSPENDED`, `STOPPING`. Check [Kafka Docs](../development/extensions-core/kafka-ingestion.html#operations) for details.|
|detailed_state|STRING|Supervisor specific state. (See documentation of the specific supervisor for details, e.g. [Kafka](../development/extensions-core/kafka-ingestion.html) or [Kinesis](../development/extensions-core/kinesis-ingestion.html))|
|healthy|LONG|Boolean represented as long type where 1 = true, 0 = false. 1 indicates a healthy supervisor|
|type|STRING|Type of supervisor, e.g. `kafka`, `kinesis` or `materialized_view`|
|source|STRING|Source of the supervisor, e.g. Kafka topic or Kinesis stream|
|suspended|LONG|Boolean represented as long type where 1 = true, 0 = false. 1 indicates supervisor is in suspended state|
|spec|STRING|JSON-serialized supervisor spec|
For example, to retrieve supervisor tasks information filtered by health status, use the query
|`druid.sql.enable`|Whether to enable SQL at all, including background metadata fetching. If false, this overrides all other SQL-related properties and disables SQL metadata, serving, and planning completely.|true|
|`druid.sql.avatica.maxConnections`|Maximum number of open connections for the Avatica server. These are not HTTP connections, but are logical client connections that may span multiple HTTP connections.|25|
|`druid.sql.avatica.maxRowsPerFrame`|Maximum number of rows to return in a single JDBC frame. Setting this property to -1 indicates that no row limit should be applied. Clients can optionally specify a row limit in their requests; if a client specifies a row limit, the lesser value of the client-provided limit and `maxRowsPerFrame` will be used.|5,000|
|`druid.sql.planner.maxTopNLimit`|Maximum threshold for a [TopN query](../querying/topnquery.md). Higher limits will be planned as [GroupBy queries](../querying/groupbyquery.md) instead.|100000|
|`druid.sql.planner.useApproximateTopN`|Whether to use approximate [TopN queries](../querying/topnquery.html) when a SQL query could be expressed as such. If false, exact [GroupBy queries](../querying/groupbyquery.html) will be used instead.|true|
|`druid.sql.planner.requireTimeCondition`|Whether to require SQL to have filter conditions on __time column so that all generated native queries will have user specified intervals. If true, all queries without filter condition on __time column will fail|false|
|`druid.sql.planner.sqlTimeZone`|Sets the default time zone for the server, which will affect how time functions and timestamp literals behave. Should be a time zone name like "America/Los_Angeles" or offset like "-08:00".|UTC|
|`druid.sql.planner.metadataSegmentCacheEnable`|Whether to keep a cache of published segments in broker. If true, broker polls coordinator in background to get segments from metadata store and maintains a local cache. If false, coordinator's REST API will be invoked when broker needs published segments info.|false|
|`druid.sql.planner.metadataSegmentPollPeriod`|How often to poll coordinator for published segments list if `druid.sql.planner.metadataSegmentCacheEnable` is set to true. Poll period is in milliseconds. |60000|
Please see [Defining SQL permissions](../development/extensions-core/druid-basic-security.html#sql-permissions) for information on what permissions are needed for making SQL queries in a secured cluster.
