# Functions and Operators

Functions and Operators (DML)

Operator | Description |

`+` `numeric` | Returns `numeric` |

`–` `numeric` | Returns negative value of `numeric` |

`numeric1` `+` `numeric2` | Sum of and `numeric1` `numeric2` |

`numeric1` `–` `numeric2` | Difference of and `numeric1` `numeric2` |

`numeric1` `*` `numeric2` | Product of and `numeric1` `numeric2` |

`numeric1` `/` `numeric2` | Quotient ( divided by `numeric1` )`numeric2` |

- 1.Parenthesization
- 2.Multiplication and division
- 3.Addition and subtraction

Operator | Description |

`=` | Equals |

`<>` | Not equals |

`>` | Greater than |

`>=` | Greater than or equal to |

`<` | Less than |

`<=` | Less than or equal to |

`BETWEEN` `x` `AND` `y` | Is a value within a range |

`NOT BETWEEN` `x` `AND` `y` | Is a value not within a range |

`IS NULL` | Is a value that is null |

`IS NOT NULL` | Is a value that is not null |

`NULLIF(` `x` `,` `y` `)` | Compare expressions x and y. If different, return x. If they are the same, return `null` . For example, if a dataset uses ‘NA’ for `null` values, you can use this statement to return `null` using `SELECT NULLIF(field_name,'NA')` . |

`IS TRUE` | True if a value resolves to TRUE. |

`IS NOT TRUE` | True if a value resolves to FALSE. |

Function | Description |

`ABS(` `x` `)` | Returns the absolute value of x |

`CEIL(` `x` `)` | Returns the smallest integer not less than the argument |

`DEGREES(` `x` `)` | Converts radians to degrees |

`EXP(` `x` `)` | Returns the value of e to the power of x |

`FLOOR(` `x` `)` | Returns the largest integer not greater than the argument |

`LN(` `x` `)` | Returns the natural logarithm of x |

`LOG(` `x` `)` | Returns the natural logarithm of x |

`LOG10(` `x` `)` | Returns the base-10 logarithm of the specified float expression x |

`MOD(` `x,y` `)` | Returns the remainder of int x divided by int y |

`PI()` | Returns the value of pi |

`POWER(` `x,y` `)` | Returns the value of x raised to the power of y |

`RADIANS(` `x` `)` | Converts degrees to radians |

`ROUND(` )`x` | Rounds x to the nearest integer value, but does not change the data type. For example, the double value 4.1 rounds to the double value 4. |

`ROUND_TO_DIGIT (` `x,y` `)` | Rounds x to y decimal places |

`SIGN(` `x` `)` | Returns the sign of x as -1, 0, 1 if x is negative, zero, or positive |

`SQRT(` `x` `)` | Returns the square root of x. |

`TRUNCATE(` `x,y` `)` | Truncates x to y decimal places |

`WIDTH_BUCKET(` `target,lower-boundary,upper-boundary,bucket-count` `)` | Define equal-width intervals (buckets) in a range between the lower boundary and the upper boundary, and returns the bucket number to which the target expression is assigned. `target` - A constant, column variable, or general expression for which a bucket number is returned.`lower-boundary` - Lower boundary for the range of values to be partitioned equally.`upper-boundary` - Upper boundary for the range of values to be partitioned equally.`partition_count` - Number of equal-width buckets in the range defined by the lower and upper boundaries.
Expressions can be constants, column variables, or general expressions. Example
Create 10 age buckets of equal size, with lower bound 0 and upper bound 100 ([0,10], [10,20]... [90,100]), and classify the age of a customer accordingly: `SELECT WIDTH_BUCKET(age, 0, 100, 10) FROM customer;` `` For example, a customer of age 34 is assigned to bucket 3 ([30,40]) and the function returns the value 3. |

Function | Description |

`ACOS(` `x` `)` | Returns the arc cosine of x |

`ASIN(` `x` `)` | Returns the arc sine of x |

`ATAN(` `x` `)` | Returns the arc tangent of x |

`ATAN2(` `y` `,` `x` `)` | Returns the arc tangent of (x, y) in the range (-π,π]. Equal to `ATAN(y/x)` for `x > 0` . |

`COS(` `x` `)` | Returns the cosine of x |

`COT(` `x` `)` | Returns the cotangent of x |

`SIN(` `x` `)` | Returns the sine of x |

`TAN(` `x` `)` | Returns the tangent of x |

Function | Description |

`DISTANCE_IN_METERS(` `fromLon` `,` `fromLat` `,` `toLon` `,` `toLat` `)` | Calculates distance in meters between two WGS84 positions. |

`CONV_4326_900913_X(` `x` `)` | Converts WGS84 latitude to WGS84 Web Mercator x coordinate. |

`CONV_4326_900913_Y(` `y` `)` | Converts WGS84 longitude to WGS84 Web Mercator y coordinate. |

Function | Description |

`BASE64_DECODE(`
`)` | Decodes a BASE64-encoded string. |

`BASE64_ENCODE(`
`)` | Encodes a string to a BASE64-encoded string. |

`CHAR_LENGTH(` `str` `)` | Returns the number of characters in a string. Only works with unencoded fields (ENCODING set to `none` ). |

|| `str1 ` [ || `str2 ` ... ]`str3` | Returns the string that results from concatenating the strings specified. Note that numeric, date, timestamp, and time types will be implicitly casted to strings as necessary, so explicit casts of non-string types to string types is not required for inputs to the concatenation operator.
Note that concatenating a variable string with a string literal, i.e. `county_name || ' County'` is significantly more performant than concatenating two or more variable strings, i.e. `county_name || ', ' || state_name. Hence for ` for multi-variable string concatenation, it is recommended to use an update statement to materialize the concatenated output rather than performing it inline when such operations are expected to be routinely repeated. |

`ENCODE_TEXT(` `none_encoded_str` `)` | Converts a none-encoded string to a transient dictionary-encoded string to allow for operations like group-by on top. When the watchdog is enabled, the number of strings that can be casted using this operator is capped by the value set with the `watchdog-none-encoded-string-translation-limit` flag (1,000,000 by default). |

`INITCAP(` `str` `)` | Returns the string with initial caps after any of the defined delimiter characters, with the remainder of the characters lowercased. Valid delimiter characters are , , , , , , , , , , , , , , , , ,
, , , , , , , , , , , . |

`JSON_VALUE(` `json_str, path` `)` | Returns the string of a field given by `path in` str. Paths start with the `$` character, with sub-fields split by `.` and array members indexed by `[]` , with array indices starting at 0. For example, `JSON_VALUE('{"name": "Brenda", "scores": [89, 98, 94]}', '$.scores[1]')` would yield a TEXT return field of `'98'` .
Note that currently`LAX` parsing mode (any unmatched path returns null rather than errors) is the default, and `STRICT` parsing mode is not supported. |

| |

`KEY_FOR_STRING(` `str` `)` | Returns the dictionary key of a dictionary-encoded string column. |

`LCASE(` `str` `)` | Returns the string in all lower case. Only ASCII character set is currently supported. Same as `LOWER` . |

`LEFT(` `str, num` `)` | Returns the left-most number ( `num` ) of characters in the string (`str` ). |

`LENGTH(` `str` `)` | Returns the length of a string in bytes. Only works with unencoded fields (ENCODING set to `none` ). |

`LOWER(` `str` `)` | Returns the string in all lower case. Only ASCII character set is currently supported. Same as `LCASE` . |

`LPAD(` `str` `, ` `len` `, [` `lpad_str` ` ])` | Left-pads the string with the string defined in `lpad_str` to a total length of `len` . If the optional `lpad_str` is not specified, the space character is used to pad.
If the length of `str` is greater than `len` , then characters from the end of `str` are truncated to the length of `len` .
Characters are added from `lpad_str` successively until the target length `len` is met. If `lpad_str` concatenated with `str` is not long enough to equal the target `len` , `lpad_str` is repeated, partially if necessary, until the target length is met. |

`LTRIM(` `str` `,` ` chars` `)` | Removes any leading characters specified in `chars` from the string. Alias for `TRIM` . |

`OVERLAY(` `str` `PLACING ` `replacement_str` `FROM ` `start` ` [FOR` `len` `])` | Replaces in `str` the number of characters defined in `len` with characters defined in `replacement_str` at the location `start` .
Regardless of the length of `replacement_str` , `len` characters are removed from `str` unless `start` + `replacement_str` is greater than the length of `str` , in which case all characters from `start` to the end of `str` are replaced.
If`start` is negative, it specifies the number of characters from the end of `str` . |

`POSITION ( `
` IN `
` [FROM `
`])` | Returns the position of the first character in `search_str` if found in `str` , optionally starting the search at `start_position` .
If `search_str` is not found, 0 is returned. If `search_str` or `str` are null, null is returned. |

`REGEXP_REPLACE(` `str` `, ` `pattern` ` [, ` `new_str` `, ` `position` `, ` `occurrence` `, [` `flags` `]])` | Replace one or all matches of a substring in string `str` that matches `pattern` , which is a regular expression in POSIX regex syntax. `` `new_str` (optional) is the string that replaces the string matching the pattern. If `new_str` is empty or not supplied, all found matches are removed. The `occurrence` integer argument (optional) specifies the single match occurrence of the pattern to replace, starting from the beginning of `str` ; 0 (replace all) is the default. Use a negative `occurrence` argument to signify the nth-to-last occurrence to be replaced. Use a positive `position` argument to indicate the number of characters from the beginning of `str` . Use a negative `position` argument to indicate the number of characters from the end of `str` . Back-references/capture groups can be used to capture and replace specific sub-expressions.
Use the following optional `flags` to control the matching behavior:
`c` - Case-sensitive matching.
`i ` - Case-insensitive matching.
If not specified, REGEXP_REPLACE defaults to case sensitive search. |

`REGEXP_SUBSTR(` `str` `, ` `pattern` ` [, ` `position` `,` ` occurrence` `, ` `flags` , `group_num` `])` | Search string `str` for `pattern` , which is a regular expression in POSIX syntax, and return the matching substring. Use `position` to set the character position to begin searching. Use `occurrence` to specify the occurrence of the pattern to match. Use a positive `position` argument to indicate the number of characters from the beginning of `str` . Use a negative `position` argument to indicate the number of characters from the end of `str` . The `occurrence` integer argument (optional) specifies the single match occurrence of the pattern to replace, with 0 being mapped to the first (1) occurrence. Use a negative `occurrence` argument to signify the nth-to-last group in `pattern` is returned. Use optional `flags` to control the matching behavior:
`c` - Case-sensitive matching.`e` - Extract submatches.
`i ` - Case-insensitive matching. The `c` and `i` flags cannot be used together; `e` can be used with either. If neither `c` nor `i` are specified, or if `pattern` is not provided, REGEXP_SUBSTR defaults to case-sensitive search. If the `e` flag is used, REGEXP_SUBSTR returns the capture group `group_num` of `pattern` matched in `str` . If the `e` flag is used, but no capture groups are provided in `pattern` , REGEXP_SUBSTR returns the entire matching `pattern` , regardless of `group_num` . If the e flag is used but no `group_num` is provided, a value of 1 for `group_num` is assumed, so the first capture group is returned. |

`REPEAT(` `str` `, ` `num` `)` | Repeats the string the number of times defined in `num` . |

`REPLACE(` `str` `, ` `from_str` `, ` `new_str` `)` | Replaces all occurrences of substring `from_str` within a string, with a new substring `new_str` . |

`REVERSE(` `str` `)` | Reverses the string. |

`RIGHT(` `str, num` `)` | Returns the right-most number ( `num` ) of characters in the string (`str` ). |

`RPAD(` `str` `, ` `len` `, ` `rpad_str` `)` | Right-pads the string with the string defined in `rpad_str` to a total length of `len` . If the optional `rpad_str` is not specified, the space character is used to pad.
If the length of `str` is greater than `len` , then characters from the beginning of `str` are truncated to the length of `len` .
Characters are added from `rpad_str` successively until the target length `len` is met. If `rpad_str` concatenated with `str` is not long enough to equal the target `len` , r`pad_str` is repeated, partially if necessary, until the target length is met. |

`RTRIM(` `str` `)` | Removes any trailing spaces from the string. |

`SPLIT_PART(` `str` `, ` `delim` `, ` `field_num` `)` | Split the string based on a delimiter `delim` and return the field identified by `field_num` . Fields are numbered from left to right. |

`STRTOK_TO_ARRAY(` `str` `, [` `delim` `])` | Tokenizes the string `str` using optional delimiter(s) `delim` and returns an array of tokens.
An empty array is returned if no tokens are produced in tokenization. NULL is returned if either parameter is a NULL. |

`SUBSTR(` `str` `, ` `start` `, [` `len` `])` | Alias for `SUBSTRING` . |

`SUBSTRING(` `str FROM` ` ` `start [ FOR` ` ` `len` `])` | Returns a substring of `str` starting at index `start` for `len` characters. The start position is 1-based (that is, the first character of `str` is at index 1, not 0). However, `start ` 0 aliases to `start` 1. If `start` is negative, it is considered to be `|start|` characters from the end of the string. If `len` is not specified, then the substring from `start` to the end of `str` is returned. If `len` is not specified, then the substring from `start` to the end of str is returned. If `start` + `len` is greater than the length of `str` , then the characters in `str` from `start` to the end of the string are returned. |

`TRIM([BOTH | LEADING | TRAILING] [` `trim_str ` `FROM ` `str` `])` | Removes characters defined in `trim_str` from the beginning, end, or both of `str` . If `trim_str` is not specified, the space character is the default.
If the trim location is not specified, defined characters are trimmed from both the beginning and end of `str` . |

TRY_CAST( str AS type) | Attempts to cast/convert a string type to any valid numeric, timestamp, date, or time type. If the conversion cannot be performed, null is returned.
Note that `TRY_CAST` is not valid for non-string input types. |

`UCASE(` `str` `)` | Returns the string in uppercase format. Only ASCII character set is currently supported. Same as `UPPER` . |

`UPPER(` `str` `)` | Returns the string in uppercase format. Only ASCII character set is currently supported. Same as `UCASE` . |

Name | Example | Description |

`str` `LIKE` `pattern` | `'ab' LIKE 'ab'` | Returns true if the string matches the pattern (case-sensitive) |

`str` `NOT LIKE` `pattern` | `'ab' NOT LIKE 'cd'` | Returns true if the string does not match the pattern |

`str` `ILIKE` `pattern` | `'AB' ILIKE 'ab'` | Returns true if the string matches the pattern (case-insensitive). Supported only when the right side is a string literal; for example, `colors.name ILIKE 'b%` |

`str` `REGEXP` `POSIX pattern` | `'^[a-z]+r$'` | Lowercase string ending with r |

`REGEXP_LIKE (` `str` `,` `POSIX pattern` `)` | `'^[hc]at'` | cat or hat |

**Usage Notes**

The following wildcard characters are supported by

`LIKE`

and `ILIKE`

:`%`

matches any number of characters, including zero characters.`_`

matches exactly one character.

Function | Description |

`CURRENT_DATE` `CURRENT_DATE()` | Returns the current date in the GMT time zone. Example: `SELECT CURRENT_DATE();` |

`CURRENT_TIME` `CURRENT_TIME()` | Returns the current time of day in the GMT time zone. Example: `SELECT CURRENT_TIME();` |

`CURRENT_TIMESTAMP` `CURRENT_TIMESTAMP()` `NOW()` | Return the current timestamp in the GMT time zone. Example: `SELECT CURRENT_TIMESTAMP();` |

`DATE_TRUNC(`
`,`
`)` | Truncates the timestamp to the specified date_part. `DATE_TRUNC(week,...)` starts on Monday (ISO), which is different than `EXTRACT(dow,...)` , which starts on Sunday.Example: `SELECT DATE_TRUNC(MINUTE, arr_timestamp) Arrival FROM flights_2008_10k LIMIT 10;` |

`EXTRACT(` `FROM`
`)` | Returns the specified date_part from timestamp.Example: `SELECT EXTRACT(HOUR FROM arr_timestamp) Arrival_Hour FROM flights_2008_10k LIMIT 10;` |

`INTERVAL`
| Adds or Subtracts count date_part units from a timestamp. Note that 'count' is enclosed in single quotes.Example: `SELECT arr_timestamp + INTERVAL '10' YEAR FROM flights_2008_10k LIMIT 10;` |

`TIMESTAMPADD(`
`,`
`,` `|`
`)` | Adds an interval of count date_part to timestamp or date and returns signed date_part units in the provided timestamp or date form.Example: `SELECT TIMESTAMPADD(DAY, 14, arr_timestamp) Fortnight FROM flights_2008_10k LIMIT 10;` |

`TIMESTAMPDIFF(`
`,`
`,`
`)` | Subtracts timestamp1 from timestamp2 and returns the result in signed date_part units.Example: `SELECT TIMESTAMPDIFF(MINUTE, arr_timestamp, dep_timestamp) Flight_Time FROM flights_2008_10k LIMIT 10;` |

`DATEDIFF(`
`,`
`,`
`)` | Returns the difference between two dates, calculated to the lowest level of the date_part you specify. For example, if you set the date_part as DAY, only the year, month, and day are used to calculate the result. Other fields, such as hour and minute, are ignored.Example: `SELECT DATEDIFF('YEAR', plane_issue_date, now()) Years_In_Service FROM flights_2008_10k LIMIT 10;` |

`DATEADD(`
`,`
`,` `|`
`)` | Returns a date after a specified time/date interval has been added. Example: `SELECT DATEADD('MINUTE', 6000, dep_timestamp) Arrival_Estimate FROM flights_2008_10k LIMIT 10;` |

`DATEPART(`
`,` `|`
`)` | Returns a specified part of a given date or timestamp as an integer value. Note that 'interval' must be enclosed in single quotes.Example: `SELECT DATEPART('YEAR', plane_issue_date) Year_Issued FROM flights_2008_10k LIMIT 10;` |

Supported

**date_part**types:DATE_TRUNC [YEAR, QUARTER, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND,

MICROSECOND, NANOSECOND, MILLENNIUM, CENTURY, DECADE, WEEK,

WEEK_SUNDAY, QUARTERDAY]

EXTRACT [YEAR, QUARTER, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND,

MICROSECOND, NANOSECOND, DOW, ISODOW, DOY, EPOCH, QUARTERDAY,

WEEK, WEEK_SUNDAY, DATEEPOCH]

DATEDIFF [YEAR, QUARTER, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND,

MICROSECOND, NANOSECOND, WEEK]

Supported

**interval**types:DATEADD [DECADE, YEAR, QUARTER, MONTH, WEEK, WEEKDAY, DAY,

HOUR, MINUTE, SECOND, MILLISECOND, MICROSECOND, NANOSECOND]

TIMESTAMPADD [YEAR, QUARTER, MONTH, WEEKDAY, DAY, HOUR, MINUTE,

SECOND, MILLISECOND, MICROSECOND, NANOSECOND]

DATEPART [YEAR, QUARTER, MONTH, DAYOFYEAR, QUARTERDAY, WEEKDAY, DAY, HOUR,

MINUTE, SECOND, MILLISECOND, MICROSECOND, NANOSECOND]

Datatype | Formats | Examples |

DATE | YYYY-MM-DD | 2013-10-31 |

DATE | MM/DD/YYYY | 10/31/2013 |

DATE | DD-MON-YY | 31-Oct-13 |

DATE | DD/Mon/YYYY | 31/Oct/2013 |

EPOCH | | 1383262225 |

TIME | HH:MM | 23:49 |

TIME | HHMMSS | 234901 |

TIME | HH:MM:SS | 23:49:01 |

TIMESTAMP | DATE TIME | 31-Oct-13 23:49:01 |

TIMESTAMP | DATETTIME | 31-Oct-13T23:49:01 |

TIMESTAMP | DATE:TIME | 11/31/2013:234901 |

TIMESTAMP | DATE TIME ZONE | 31-Oct-13 11:30:25 -0800 |

TIMESTAMP | DATE HH.MM.SS PM | 31-Oct-13 11.30.25pm |

TIMESTAMP | DATE HH:MM:SS PM | 31-Oct-13 11:30:25pm |

TIMESTAMP | | 1383262225 |

- For two-digit years, years 69-99 are assumed to be previous century (for example, 1969), and 0-68 are assumed to be current century (for example, 2016).
- For four-digit years, negative years (BC) are not supported.
- Hours are expressed in 24-hour format.
- When time components are separated by colons, you can write them as one or two digits.
- Months are case insensitive. You can spell them out or abbreviate to three characters.
- For timestamps, decimal seconds are ignored. Time zone offsets are written as +/-HHMM.
- For timestamps, a numeric string is converted to +/- seconds since January 1, 1970. Supported timestamps range from -30610224000 (January 1, 1000) through 29379456000 (December 31, 2900).
- On output, dates are formatted as YYYY-MM-DD. Times are formatted as HH:MM:SS.
- Linux EPOCH values range from -30610224000 (1/1/1000) through 185542587100800 (1/1/5885487). Complete range in years: +/-5,883,517 around epoch.

Both double-precision (standard) and single-precision floating point statistical functions are provided. Single-precision functions run faster on GPUs but might cause overflow errors.

Double-precision FP Function | Single-precision FP Function | Description |

`AVG(`
`)` | | Returns the average value of x |

`COUNT()` | | Returns the count of the number of rows returned |

`COUNT(DISTINCT`
`)` | | Returns the count of distinct values of x |

`APPROX_COUNT_DISTINCT(`
`,`
`)` | | Returns the approximate count of distinct values of x with defined expected error rate e, where e is an integer from 1 to 100. If no value is set for e, the approximate count is calculated using the system-wide`hll-precision-bits` configuration parameter. |

`APPROX_MEDIAN(`
`)` | | Returns the approximate median of x. Two server configuration parameters affect memory usage: |

`APPROX_PERCENTILE(`
`,`
`)` | | Returns the approximate quantile of , where `x` is the value between 0 and 1.`y` For example, `y=0` returns `MIN(x)` , `y=1` returns `MAX(x)` , and `y=0.5` returns `APPROX_MEDIAN(x)` . |

`MAX(`
`)` | | Returns the maximum value of x |

`MIN(`
`)` | | Returns the minimum value of x |

`SINGLE_VALUE` | | Returns the input value if there is only one distinct value in the input; otherwise, the query fails. |

`SUM(`
`)` | | Returns the sum of the values of x |

`SAMPLE(`
`)` | | Returns one sample value from aggregated column x. For example, the following query returns population grouped by city, along with one value from the state column for each group:Note: This was previously `LAST_SAMPLE` , which is now deprecated. |

`CORRELATION(x, y)` | `CORRELATION_FLOAT(x, y)` | Alias of CORR. Returns the coefficient of correlation of a set of number pairs. |

`CORR(x, y)` | `CORR_FLOAT(x, y)` | Returns the coefficient of correlation of a set of number pairs. |

`COUNT_IF(conditional_expr)` | | Returns the number of rows satisfying the given `condition_expr` . |

`COVAR_POP(x, y)` | `COVAR_POP_FLOAT(x, y)` | Returns the population covariance of a set of number pairs. |

`COVAR_SAMP(x, y)` | `COVAR_SAMP_FLOAT(x, y)` | Returns the sample covariance of a set of number pairs. |

`STDDEV(x)` | `STDDEV_FLOAT(x)` | Alias of STDDEV_SAMP. Returns sample standard deviation of the value. |

`STDDEV_POP(x)` | `STDDEV_POP_FLOAT(x)` | Returns the population standard the standard deviation of the value. |

`STDDEV_SAMP(x)` | `STDDEV_SAMP_FLOAT(x)` | Returns the sample standard deviation of the value. |

`SUM_IF(conditional_expr)` | | Returns the sum of all expression values satisfying the given `condition_expr` . |

`VARIANCE(x)` | `VARIANCE_FLOAT(x)` | Alias of VAR_SAMP. Returns the sample variance of the value. |

`VAR_POP(x)` | `VAR_POP_FLOAT(x)` | Returns the population variance sample variance of the value. |

`VAR_SAMP(x)` | `VAR_SAMP_FLOAT(x)` | Returns the sample variance of the value. |

`COUNT(DISTINCT`

`x`

`)`

, especially when used in conjunction with GROUP BY, can require a very large amount of memory to keep track of all distinct values in large tables with large cardinalities. To avoid this large overhead, use APPROX_COUNT_DISTINCT.`APPROX_COUNT_DISTINCT(`

`x`

`,`

`e`

`)`

gives an approximate count of the value**x**, based on an expected error rate defined in**e**. The error rate is an integer value from 1 to 100. The lower the value of**e**, the higher the precision, and the higher the memory cost. Select a value for**e**based on the level of precision required. On large tables with large cardinalities, consider using`APPROX_COUNT_DISTINCT`

when possible to preserve memory. When data cardinalities permit, OmniSci uses the precise implementation of`COUNT(DISTINCT`

`x`

`)`

for`APPROX_COUNT_DISTINCT`

. Set the default error rate using the`-hll-precision-bits`

configuration parameter.- The accuracy of
`APPROX_MEDIAN (`

`x`

`)`

upon the distribution of data. For example:- For 100,000,000 integers (1, 2, 3, ... 100M) in random order, APPROX_MEDIAN can provide a highly accurate answer 5+ significant digits.
- For 100,000,001 integers, where 50,000,000 have value of 0 and 50,000,001 have value of 1, APPROX_MEDIAN returns a value close to 0.5, even though the median is 1.

- Currently, OmniSci does not support grouping by non-dictionary-encoded strings. However, with the
`SAMPLE`

aggregate function, you can select non-dictionary-encoded strings that are presumed to be unique in a group. For example:SELECT user_name, SAMPLE(user_decription) FROM tweets GROUP BY user_name;If the aggregated column (user_description in the example above) is not unique within a group,`SAMPLE`

selects a value that might be nondeterministic because of the parallel nature of OmniSci query execution.

Function | Description |

`SAMPLE_RATIO(`
`)` | Returns a Boolean value, with the probability of `True` being returned for a row equal to the input argument. The input argument is a numeric value between 0.0 and 1.0. Negative input values (return `False` ), input values greater than 1.0 returns `True` , and null input values return `False` .The result of the function is deterministic per row; that is, all calls of the operator for a given row return the same result. The sample ratio is probabilistic, but is generally within a thousandth of a percentile of the actual range when the underlying dataset is millions of records or larger. The following example filters approximately 50% of the rows from `t` and returns a count that is approximately half the number of rows in `t` :`SELECT COUNT(*) FROM t WHERE SAMPLE_RATIO(0.5)` |

You can create your own C++ functions and use them in your SQL queries.

- User-defined Functions (UDFs) require clang++ version 9. You can verify the version installed using the command
`clang++ --version`

. - UDFs currently allow any authenticated user to register and execute a runtime function. By default, runtime UDFs are globally disabled but can be enabled with the runtime flag
`enable-runtime-udf`

.

- 1.Create your function and save it in a .cpp file; for example, /var/lib/omnisci/udf_myFunction.cpp.
- 2.Add the UDF configuration flag to omnisci.conf. For example:udf = "/var/lib/omnisci/udf_myFunction.cpp"
- 3.Use your function in a SQL query. For example:SELECT udf_myFunction FROM myTable

This function, udf_diff.cpp, returns the difference of two values from a table.

#include <cstdint>

#if defined(__CUDA_ARCH__) && defined(__CUDACC__) && defined(__clang__)

#define DEVICE __device__

#define NEVER_INLINE

#define ALWAYS_INLINE

#else

#define DEVICE

#define NEVER_INLINE __attribute__((noinline))

#define ALWAYS_INLINE __attribute__((always_inline))

#endif

#define EXTENSION_NOINLINE extern "C" NEVER_INLINE DEVICE

EXTENSION_NOINLINE int32_t udf_diff(const int32_t x, const int32_t y) { return x - y; }

Include the standard integer library, which supports the following datatypes:

- bool
- int8_t (cstdint), char
- int16_t (cstdint), short
- int32_t (cstdint), int
- int64_t (cstdint), size_t
- float
- double
- void

#include <cstdint>

The next four lines are boilerplate code that allows OmniSci to determine whether the server is running with GPUs. OmniSci chooses whether it should compile the function inline to achieve the best possible performance.

#include <cstdint>

#if defined(__CUDA_ARCH__) && defined(__CUDACC__) && defined(__clang__)

#define DEVICE __device__

#define NEVER_INLINE

#define ALWAYS_INLINE

#else

#define DEVICE

#define NEVER_INLINE __attribute__((noinline))

#define ALWAYS_INLINE __attribute__((always_inline))

#endif

#define EXTENSION_NOINLINE extern "C" NEVER_INLINE DEVICE

The next line is the actual user-defined function, which returns the difference between INTEGER values x and y.

EXTENSION_NOINLINE int32_t udf_diff(const int32_t x, const int32_t y) { return x - y; }

To run the

`udf_diff`

function, add this line to your /var/lib/omnisci/omnisci.conf file (in this example, the .cpp file is stored at /var/lib/omnisci/udf_diff.cpp):udf = "/var/lib/omnisci/udf_diff.cpp"

Restart the OmniSci server.

Use your command from an OmniSci SQL client to query, for example, a table named myTable that contains the INTEGER columns

`myInt1`

and `myInt2`

.SELECT udf_diff(myInt1, myInt2) FROM myTable LIMIT 1;

OmniSci returns the difference as an INTEGER value.

Last modified 1mo ago