# Functions and Operators

## Basic Mathematical Operators

Operator Description
`+numeric` Returns numeric
`–numeric` Returns negative value of numeric
`numeric1 + numeric2` Sum of numeric1 and numeric2
`numeric1 – numeric2` Difference of numeric1 and numeric2
`numeric1 * numeric2` Product of numeric1 and numeric2
`numeric1 / numeric2` Quotient (numeric1 divided by numeric2)

#### Mathematical Operator Precedence

1. Parenthesization
2. Multiplication and division

## Comparison Operators

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.

## Mathematical Functions

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

## Trigonometric Functions

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(x, y)` Returns the arc tangent of x and y
`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

## Geometric Functions

Function Description
```DISTANCE_IN_METERS(fromLon, fromLat, toLon, toLat)``` Calculates distance in meters between two WGS-84 positions.
`CONV_4326_900913_X(x)` Converts WGS-84 latitude to WGS-84 Web Mercator x coordinate.
`CONV_4326_900913_Y(y)` Converts WGS-84 longitude to WGS-84 Web Mercator y coordinate.

## String Functions

Function Description
`CHAR_LENGTH(str)` Returns the number of characters in a string
`LENGTH(str)` Returns the length of a string in bytes
 Note String functions only work with unencoded fields (ENCODING set to `none`).

## Pattern-matching Functions

Name Example Description
`str LIKE pattern` `'ab' LIKE 'ab'` Returns true if the string matches the pattern
`str NOT LIKE pattern` `'ab' NOT LIKE 'cd'` Returns true if the string does not match the pattern
`str ILIKE pattern` `'AB' ILIKE 'ab'` Case-insensitive LIKE
`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.

## Date/Time Functions

Function Description
```DATE_TRUNC(date_part, timestamp)``` Truncates the timestamp to the specified date_part. Note that date_part is not enclosed in single quotes.
Example
```SELECT DATE_TRUNC(MINUTE, arr_timestamp) Arrival \
FROM flights_2008_10k LIMIT 10;```
```EXTRACT(date_part FROM timestamp)``` Returns the specified date_part from timestamp. Note that date_part is not enclosed in single quotes.
Example
```SELECT EXTRACT(HOUR FROM arr_timestamp) Arrival_Hour \
FROM flights_2008_10k LIMIT 10;```
`INTERVAL 'count' date_part` Adds or Subtracts count date_part units from a timestamp. Note that 'count' is enclosed in single quotes and date_part is not enclosed in single quotes.
Example
```SELECT arr_timestamp + INTERVAL '10' YEAR \
FROM flights_2008_10k LIMIT 10;```
`NOW()` Returns the current timestamp.
Example
`SELECT NOW() FROM flights_2008_10k LIMIT 1;`
```TIMESTAMPADD(date_part, count, timestamp | date)``` Adds an interval of count date_part to timestamp or date and returns signed date_part units in the provided timestamp or date form. Note that neither count nor date_part are enclosed in single quotes.
Example
```SELECT TIMESTAMPADD(DAY, 14, arr_timestamp) Fortnight \
FROM flights_2008_10k LIMIT 10;```
```TIMESTAMPDIFF(date_part, timestamp1, timestamp2)``` Subtracts timestamp1 from timestamp2 and returns the result in signed date_part units. Note that date_part is not enclosed in single quotes.
Example
```SELECT TIMESTAMPDIFF(MINUTE, arr_timestamp, dep_timestamp) Flight_Time \
FROM flights_2008_10k LIMIT 10;```
```DATEDIFF('date_part', date, date)``` 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.

Note that 'date_part' must be enclosed in single quotes.
Example
```SELECT DATEDIFF('YEAR', plane_issue_date, now()) Years_In_Service \
FROM flights_2008_10k LIMIT 10;```
```DATEADD('date_part', interval, date | timestamp)``` Returns a date after a specified time/date interval has been added. Note that 'date_part' must be enclosed in single quotes.
Example
```SELECT DATEADD('MINUTE', 6000, dep_timestamp) Arrival_Estimate \
FROM flights_2008_10k LIMIT 10;```
`DATEPART('interval', date | timestamp)` 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;```

### Usage Notes

Supported date_part types:

```DATE_TRUNC [YEAR, QUARTER, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND,
MICROSECOND, NANOSECOND, MILLENNIUM, CENTURY, DECADE, WEEK,
QUARTERDAY]
EXTRACT    [YEAR, QUARTER, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND,
MICROSECOND, NANOSECOND, DOW, ISODOW, DOY, EPOCH, QUARTERDAY,
WEEK]
DATEDIFF   [YEAR, QUARTER, MONTH, DAY, HOUR, MINUTE, SECOND, MILLISECOND,
MICROSECOND, NANOSECOND, MILLENNIUM, CENTURY, DECADE, WEEK,
QUARTERDAY]
```

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]
```

### Accepted Date, Time, and Timestamp Formats

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

#### Usage Notes

• 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.

## Statistical and Aggregate Functions

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(x)` Returns the average value of x
`COUNT()` Returns the count of the number of rows returned
`COUNT(DISTINCT x)` Returns the count of distinct values of x
`APPROX_COUNT_DISTINCT(x, e)` Returns the approximate count of distinct values of x with defined expected error rate e
`MAX(x)` Returns the maximum value of x
`MIN(x)` Returns the minimum value of x
`SUM(x)` Returns the sum of the values of x
`SAMPLE(x)` 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:
```SELECT city, SAMPLE(state), sum (population)
FROM census_table
GROUP BY city```

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.
`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.
`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.

#### Usage Notes

• `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 paramenter.
• 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.

## User-defined Functions

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

 Note User-defined Functions (UDFs) require `clang++` version 7 or higher. 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`

### Sample User-defined Function

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

```#include <cstdint>
#if defined(clang) && defined(CUDA) && defined(CUDA_ARCH) #define DEVICE device #else #define DEVICE #endif
#if defined(clang) && defined(CUDA) && defined(CUDA_ARCH) #define NEVER_INLINE #else #define NEVER_INLINE attribute((noinline)) #endif
#if defined(clang) && defined(CUDA) && defined(CUDA_ARCH) #define ALWAYS_INLINE #else #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; }```

#### Code Commentary.

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 five 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.

```#if defined(clang) && defined(CUDA) && defined(CUDA_ARCH) #define DEVICE device #else #define DEVICE #endif
#if defined(clang) && defined(CUDA) && defined(CUDA_ARCH) #define NEVER_INLINE #else #define NEVER_INLINE attribute((noinline)) #endif
#if defined(clang) && defined(CUDA) && defined(CUDA_ARCH) #define ALWAYS_INLINE #else #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.