homework-jianmu/10-function.md at 7ce5fb11b09b51dfa1f1e8e93794e65344185f54

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Functions	4

Single-Row Functions

Single-Row functions return a result row for each row in the query result.

Numeric Functions

ABS

SELECT ABS(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The absolute value of a specific field.

Return value type: Same as input type.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Cannot be used with aggregate functions.

ACOS

SELECT ACOS(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The anti-cosine of a specific field.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Cannot be used with aggregate functions.

ASIN

SELECT ASIN(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The anti-sine of a specific field.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable

Applicable nested query: Inner query and Outer query.

More explanations:

Cannot be used with aggregate functions.

ATAN

SELECT ATAN(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: anti-tangent of a specific field.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable

Applicable nested query: Inner query and Outer query.

More explanations:

Cannot be used with aggregate functions.

CEIL

SELECT CEIL(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The rounded up value of a specific field.

Return value type: Same as input type.

Applicable data types: Numeric types.

Applicable table types: table, STable

Applicable nested query: Inner query and outer query.

More explanations:

Can't be used with aggregate functions.

COS

SELECT COS(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The cosine of a specific field.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Can't be used with aggregate functions.

FLOOR

SELECT FLOOR(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The rounded down value of a specific field.

More explanations: Refer to CEIL function for usage restrictions.

LOG

SELECT LOG(field_name, base) FROM { tb_name | stb_name } [WHERE clause]

Description: The logarithm of a specific field with base as the radix. If base parameter is ignored, natural logarithm of the field is returned.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Can't be used with aggregate functions

POW

SELECT POW(field_name, power) FROM { tb_name | stb_name } [WHERE clause]

Description: The power of a specific field with power as the index.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Can't be used with aggregate functions.

ROUND

SELECT ROUND(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The rounded value of a specific field.

More explanations: Refer to CEIL function for usage restrictions.

SIN

SELECT SIN(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The sine of a specific field.

Description: The anti-cosine of a specific field.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Can't be used with aggregate functions.

SQRT

SELECT SQRT(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The square root of a specific field.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Can't be used with aggregate functions.

TAN

SELECT TAN(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The tangent of a specific field.

Description: The anti-cosine of a specific field.

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Can't be used with aggregate functions.

String Functions

String functiosn take strings as input and output numbers or strings.

CHAR_LENGTH

SELECT CHAR_LENGTH(str|column) FROM { tb_name | stb_name } [WHERE clause]

Description: The mumber of characters of a string.

Return value type: INTEGER.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

CONCAT

SELECT CONCAT(str1|column1, str2|column2, ...) FROM { tb_name | stb_name } [WHERE clause]

Description: The concatenation result of two or more strings.

Return value type: If all input strings are VARCHAR type, the result is VARCHAR type too. If any one of input strings is NCHAR type, then the result is NCHAR. If input strings contain NULL value, the result is NULL.

Applicable data types: VARCHAR, NCHAR. At least 2 input strings are requird, and at most 8 input strings are allowed.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

CONCAT_WS

SELECT CONCAT_WS(separator, str1|column1, str2|column2, ...) FROM { tb_name | stb_name } [WHERE clause]

Description: The concatenation result of two or more strings with separator.

Applicable data types: VARCHAR, NCHAR. At least 3 input strings are requird, and at most 9 input strings are allowed.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

LENGTH

SELECT LENGTH(str|column) FROM { tb_name | stb_name } [WHERE clause]

Description: The length in bytes of a string.

Return value type: INTEGER.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

LOWER

SELECT LOWER(str|column) FROM { tb_name | stb_name } [WHERE clause]

Description: Convert the input string to lower case.

Return value type: Same as input type.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

LTRIM

SELECT LTRIM(str|column) FROM { tb_name | stb_name } [WHERE clause]

Description: Remove the left leading blanks of a string.

Return value type: Same as input type.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

RTRIM

SELECT RTRIM(str|column) FROM { tb_name | stb_name } [WHERE clause]

Description: Remove the right tailing blanks of a string.

Return value type: Same as input type.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

SUBSTR

SELECT SUBSTR(str,pos[,len]) FROM { tb_name | stb_name } [WHERE clause]

Description: The sub-string starting from pos with length of len from the original string str.

Return value type: Same as input type.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

If the input is NULL, the output is NULL
Parameter pos can be an positive or negative integer; If it's positive, the starting position will be counted from the beginning of the string; if it's negative, the starting position will be counted from the end of the string.
If len is not specified, it means from pos to the end of string.

UPPER

SELECT UPPER(str|column) FROM { tb_name | stb_name } [WHERE clause]

Description: Convert the input string to upper case.

Return value type: Same as input type.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

Conversion Functions

Conversion functions convert from one data type to another.

CAST

SELECT CAST(expression AS type_name) FROM { tb_name | stb_name } [WHERE clause]

Description: Used for type casting. Convert expression to the type specified by type_name.

Return value type: The type specified by parameter type_name.

Applicable data types: expression can be any data type except for JSON.

More explanations:

Error will be reported for unsupported type casting.
Some values of some supported data types may not be casted, below are known issues: 1）When casting VARCHAR/NCHAR to BIGINT/BIGINT UNSIGNED, some characters may be treated as illegal, for example "a" may be converted to 0. 2）When casting to numeric type, if converted result is out of range the destination data type can hold, overflow may occur and casting behavior is undefined. 3) When casting to VARCHAR/NCHAR type, if converted string length exceeds the length specified in type_name, the result will be truncated. (e.g. CAST("abcd" as BINARY(2)) will return string "ab").

TO_ISO8601

SELECT TO_ISO8601(ts[, timezone]) FROM { tb_name | stb_name } [WHERE clause];

Description: The ISO8601 date/time format converted from a UNIX timestamp, with timezone attached. timezone parameter allows attaching any customized timezone string to the output format. If timezone parameter is not specified, the timezone information of client side system will be attached.

Return value type: VARCHAR.

Applicable data types: INTEGER, TIMESTAMP.

Applicable table types: table, STable.

More explanations:

If the input is INTEGER represents UNIX timestamp, the precision of the returned value is determined by the digits of the input integer.
If the input is of TIMESTAMP type, The precision of the returned value is same as the precision set for the current database in use.

TO_JSON

SELECT TO_JSON(str_literal) FROM { tb_name | stb_name } [WHERE clause];

Description: Convert a JSON string to a JSON body.

Return value type: JSON.

Applicable data types: JSON string, in the format like '{ "literal" : literal }'. '{}' is NULL value. keys in the string must be string constants, values can be constants of numeric types, bool, string or NULL. Escaping characters are not allowed in the JSON string.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

TO_UNIXTIMESTAMP

SELECT TO_UNIXTIMESTAMP(datetime_string | ts_col) FROM { tb_name | stb_name } [WHERE clause];

Description: UNIX timestamp converted from a string of date/time format.

Return value type: BIGINT.

Applicable data types: VARCHAR, NCHAR.

Applicable table types: table, STable.

More explanations:

The input string must be compatible with ISO8601/RFC3339 standard, NULL will be returned if the string cannot be converted.
The precision of the returned timestamp is same as the precision set for the current database in use.

DateTime Functions

DateTime functions applied to timestamp data. NOW(), TODAY() and TIMEZONE() are executed only once even though they may occur multiple times in a single SQL statement.

NOW

SELECT NOW() FROM { tb_name | stb_name } [WHERE clause];
SELECT select_expr FROM { tb_name | stb_name } WHERE ts_col cond_operatior NOW();
INSERT INTO tb_name VALUES (NOW(), ...);

Description: The current time of the client side system.

Return value type: TIMESTAMP.

Applicable data types: TIMESTAMP only if used in WHERE/INSERT clause.

Applicable table types: table, STable.

More explanations:

Addition and Subtraction operation with time duration can be performed, for example NOW() + 1s, the time unit can be one of the followings: b(nanosecond), u(microsecond), a(millisecond)), s(second), m(minute), h(hour), d(day), w(week).
The precision of the returned timestamp is same as the precision set for the current database in use.

TIMEDIFF

SELECT TIMEDIFF(ts1 | datetime_string1, ts2 | datetime_string2 [, time_unit]) FROM { tb_name | stb_name } [WHERE clause];

Description: The difference(duration) between two timestamps, and rounded to the time unit specified by time_unit.

Return value type: BIGINT.

Applicable data types: INTEGER/TIMESTAMP represents UNIX timestamp, or VARCHAR/NCHAR string in date/time format.

Applicable table types: table, STable.

More explanations:

Time unit specified by time_unit can be: 1b(nanosecond), 1u(microsecond),1a(millisecond),1s(second),1m(minute),1h(hour),1d(day),1w(week).
If time_unit parameter is not specified, the precision of the returned time duration is same as the precision set for the current database in use.

TIMETRUNCATE

SELECT TIMETRUNCATE(ts_val | datetime_string | ts_col, time_unit) FROM { tb_name | stb_name } [WHERE clause];

Description: Truncate the input timestamp with unit specified by time_unit.

Return value type: TIMESTAMP.

Applicable data types: INTEGER/TIMESTAMP represents UNIX timestamp, or VARCHAR/NCHAR string in date/time format.

Applicable table types: table, STable.

More explanations:

Time unit specified by time_unit can be: 1b(nanosecond),1u(microsecond),1a(millisecond),1s(second),1m(minute),1h(hour),1d(day),1w(week).
The precision of the returned timestamp is same as the precision set for the current database in use.

TIMEZONE

SELECT TIMEZONE() FROM { tb_name | stb_name } [WHERE clause];

Description: The timezone of the client side system.

Return value type: VARCHAR.

Applicable data types: None.

Applicable table types: table, STable.

TODAY

SELECT TODAY() FROM { tb_name | stb_name } [WHERE clause];
SELECT select_expr FROM { tb_name | stb_name } WHERE ts_col cond_operatior TODAY()];
INSERT INTO tb_name VALUES (TODAY(), ...);

Description: The timestamp of 00:00:00 of the client side system.

Return value type: TIMESTAMP.

Applicable data types: TIMESTAMP only if used in WHERE/INSERT clause.

Applicable table types: table, STable.

More explanations:

Addition and Subtraction operation can be performed with time durations, for example NOW() + 1s, the time unit can be: b(nanosecond), u(microsecond), a(millisecond)), s(second), m(minute), h(hour), d(day), w(week).
The precision of the returned timestamp is same as the precision set for the current database in use.

Aggregate Functions

Aggregate functions return single result row for each group in the query result set. Groups are determined by GROUP BY clause or time window clause if they are used; or the whole result is considered a group if neither of them is used.

APERCENTILE

SELECT APERCENTILE(field_name, P[, algo_type])
FROM { tb_name | stb_name } [WHERE clause]

Description: Similar to PERCENTILE, but a approximated result is returned.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations

P is in range [0,100], when P is 0, the result is same as using function MIN; when P is 100, the result is same as function MAX.
algo_type can only be input as default or t-digest, if it's not specified default will be used, i.e. apercentile(column_name, 50) is same as apercentile(column_name, 50, "default").
If default is used, histogram based algorithm is used for calculation. If t-digest is used, t-digest sampling algorithm is used to calculate the result.

Nested query: It can be used in both the outer query and inner query in a nested query.

AVG

SELECT AVG(field_name) FROM tb_name [WHERE clause];

Description: Get the average value of a column in a table or STable.

Return value type: DOUBLE.

Applicable data types: Numeric type.

Applicable table types: table, STable.

COUNT

SELECT COUNT([*|field_name]) FROM tb_name [WHERE clause];

Description: Get the number of rows in a table or a super table.

Return value type: BIGINT.

Applicable data types: All data types.

Applicable table types: table, STable.

More explanation:

Wildcard (*) is used to represent all columns. If * used COUNT function will get the total number of all rows.
The number of non-NULL values will be returned if this function is used on a specific column.

ELAPSED

SELECT ELAPSED(field_name[, time_unit]) FROM { tb_name | stb_name } [WHERE clause] [INTERVAL(interval [, offset]) [SLIDING sliding]];

Description：elapsed function can be used to calculate the continuous time length in which there is valid data. If it's used with INTERVAL clause, the returned result is the calcualted time length within each time window. If it's used without INTERVAL caluse, the returned result is the calculated time duration within the specified time range. Please be noted that the calculated time duration is in the specified time_unit.

Return value type：DOUBLE.

Applicable Column type：TIMESTAMP.

Applicable tables: table, STable, outter in nested query.

Explanations：

field_name parameter can only be the first column of a table, i.e. timestamp primary key.
The minimum value of time_unit is the time precision of the database. If time_unit is not specified, the time precision of the database is used as the default ime unit.
It can be used with INTERVAL to get the time valid time length of each time window. Please be noted that the return value is same as the time window for all time windows except for the first and the last time window.
order by asc/desc has no effect on the result.
group by tbname must be used together when elapsed is used against a STable.
group by must NOT be used together when elapsed is used against a table or sub table.
When used in nested query, it's only applicable when the inner query outputs an implicit timestamp column as the primary key. For example, select elapsed(ts) from (select diff(value) from sub1) is legal usage while select elapsed(ts) from (select * from sub1) is not.
It cannot be used with leastsquares, diff, derivative, top, bottom, last_row, interp.

LEASTSQUARES

SELECT LEASTSQUARES(field_name, start_val, step_val) FROM tb_name [WHERE clause];

Description: The linear regression function of the specified column and the timestamp column (primary key), start_val is the initial value and step_val is the step value.

Return value type: VARCHAR string in the format of "(slope, intercept)".

Applicable data types: Numeric types.

Applicable table types: table only.

SPREAD

SELECT SPREAD(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The difference between the max and the min value of a specific column.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations: Can be used on a column of TIMESTAMP type, the result time unit precision is same as the current database in use.

STDDEV

SELECT STDDEV(field_name) FROM tb_name [WHERE clause];

Description: Standard deviation of a specific column in a table or STable.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table, STable.

SUM

SELECT SUM(field_name) FROM tb_name [WHERE clause];

Description: The summation of values of a specific column in a table or STable.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table, STable.

HYPERLOGLOG

SELECT HYPERLOGLOG(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description:The cardinal number of a specific column is returned by using hyperloglog algorithm.

Return value type: INTEGER.

Applicable column types: All data types.

More explanations: The benefit of using hyperloglog algorithm is that the memory usage is under control when the data volume is huge. However, when the data volume is very small, the result may be not accurate, it's recommented to use select count(data) from (select unique(col) as data from table) in this case.

HISTOGRAM

SELECT HISTOGRAM(field_name，bin_type, bin_description, normalized) FROM tb_name [WHERE clause];

Description：Returns count of data points in user-specified ranges.

Return value type：DOUBLE or BIGINT, depends on normalized parameter settings.

Applicable column type：Numerical types.

Applicable table types: table, STable.

Explanations：

bin_type: parameter to indicate the bucket type, valid inputs are: "user_input", "linear_bin", "log_bin"。
bin_description: parameter to describe the rule to generate buckets，can be in the following JSON formats for each bin_type respectively:
- "user_input": "[1, 3, 5, 7]": User specified bin values.
- "linear_bin": "{"start": 0.0, "width": 5.0, "count": 5, "infinity": true}" "start" - bin starting point. "width" - bin offset. "count" - number of bins generated. "infinity" - whether to add（-inf, inf）as start/end point in generated set of bins. The above "linear_bin" descriptor generates a set of bins: [-inf, 0.0, 5.0, 10.0, 15.0, 20.0, +inf].
- "log_bin": "{"start":1.0, "factor": 2.0, "count": 5, "infinity": true}" "start" - bin starting point. "factor" - exponential factor of bin offset. "count" - number of bins generated. "infinity" - whether to add（-inf, inf）as start/end point in generated range of bins. The above "log_bin" descriptor generates a set of bins:[-inf, 1.0, 2.0, 4.0, 8.0, 16.0, +inf].
normalized: setting to 1/0 to turn on/off result normalization.

PERCENTILE

SELECT PERCENTILE(field_name, P) FROM { tb_name } [WHERE clause];

Description: The value whose rank in a specific column matches the specified percentage. If such a value matching the specified percentage doesn't exist in the column, an interpolation value will be returned.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table.

More explanations: P is in range [0,100], when P is 0, the result is same as using function MIN; when P is 100, the result is same as function MAX.

Selector Functions

Selector functiosn choose one or more rows in the query result according to the semantics. You can specify to output primary timestamp column and other columns including tbname and tags so that you can easily know which rows the selected values belong to.

BOTTOM

SELECT BOTTOM(field_name, K) FROM { tb_name | stb_name } [WHERE clause];

Description: The least k values of a specific column in a table or STable. If a value has multiple occurrences in the column but counting all of them in will exceed the upper limit k, then a part of them will be returned randomly.

Return value type: Same as the column being operated upon.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations:

k must be in range [1,100].
The timestamp associated with the selected values are returned too.
Can't be used with FILL.

FIRST

SELECT FIRST(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The first non-null value of a specific column in a table or STable.

Return value type: Same as the column being operated upon.

Applicable column types: All data types.

Applicable table types: table, STable.

More explanations:

FIRST(*) can be used to get the first non-null value of all columns
NULL will be returned if all the values of the specified column are all NULL
A result will NOT be returned if all the columns in the result set are all NULL

INTERP

SELECT INTERP(field_name) FROM { tb_name | stb_name } [WHERE where_condition] [ RANGE(timestamp1,timestamp2) ] [EVERY(interval)] [FILL ({ VALUE | PREV | NULL | LINEAR | NEXT})];

Description: The value that matches the specified timestamp range is returned, if existing; or an interpolation value is returned.

Return value type: Same as the column being operated upon.

Applicable column types: Numeric data types.

Applicable table types: table, STable, nested query.

More explanations

INTERP is used to get the value that matches the specified time slice from a column. If no such value exists an interpolation value will be returned based on FILL parameter.
The input data of INTERP is the value of the specified column and a where clause can be used to filter the original data. If no where condition is specified then all original data is the input.
The output time range of INTERP is specified by RANGE(timestamp1,timestamp2) parameter, with timestamp1<=timestamp2. timestamp1 is the starting point of the output time range and must be specified. timestamp2 is the ending point of the output time range and must be specified. If RANGE is not specified, then the timestamp of the first row that matches the filter condition is treated as timestamp1, the timestamp of the last row that matches the filter condition is treated as timestamp2.
The number of rows in the result set of INTERP is determined by the parameter EVERY. Starting from timestamp1, one interpolation is performed for every time interval specified EVERY parameter. If EVERY parameter is not used, the time windows will be considered as no ending timestamp, i.e. there is only one time window from timestamp1.
Interpolation is performed based on FILL parameter. No interpolation is performed if FILL is not used, that means either the original data that matches is returned or nothing is returned.
INTERP can only be used to interpolate in single timeline. So it must be used with group by tbname when it's used on a STable. It can't be used with GROUP BY when it's used in the inner query of a nested query.
The result of INTERP is not influenced by ORDER BY TIMESTAMP, which impacts the output order only..

LAST

SELECT LAST(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The last non-NULL value of a specific column in a table or STable.

Return value type: Same as the column being operated upon.

Applicable column types: All data types.

Applicable table types: table, STable.

More explanations:

LAST(*) can be used to get the last non-NULL value of all columns
If the values of a column in the result set are all NULL, NULL is returned for that column; if all columns in the result are all NULL, no result will be returned.
When it's used on a STable, if there are multiple values with the timestamp in the result set, one of them will be returned randomly and it's not guaranteed that the same value is returned if the same query is run multiple times.

LAST_ROW

SELECT LAST_ROW(field_name) FROM { tb_name | stb_name };

Description: The last row of a table or STable.

Return value type: Same as the column being operated upon.

Applicable column types: All data type.

Applicable table types: table, STable.

More explanations:

When it's used against a STable, multiple rows with the same and largest timestamp may exist, in this case one of them is returned randomly and it's not guaranteed that the result is same if the query is run multiple times.
Cannot be used with INTERVAL.

MAX

SELECT MAX(field_name) FROM { tb_name | stb_name } [WHERE clause];

Description: The maximum value of a specific column of a table or STable.

Return value type: Same as the data type of the column being operated upon.

Applicable column types: Numeric types.

Applicable table types: table, STable.

MIN

SELECT MIN(field_name) FROM {tb_name | stb_name} [WHERE clause];

Description: The minimum value of a specific column in a table or STable.

Return value type: Same as the data type of the column being operated upon.

Applicable column types: Numeric types.

Applicable table types: table, STable.

MODE

SELECT MODE(field_name) FROM tb_name [WHERE clause];

Description:The value which has the highest frequency of occurrence. NULL is returned if there are multiple values which have highest frequency of occurrence.

Return value type:Same as the data type of the column being operated upon.

Applicable column types: All data types.

More explanations:Considering the number of returned result set is unpredictable, it's suggested to limit the number of unique values to 100,000, otherwise error will be returned.

SAMPLE

    SELECT SAMPLE(field_name, K) FROM { tb_name | stb_name } [WHERE clause]

Description: k sampling values of a specific column. The applicable range of k is [1,1000].

Return value type: Same as the column being operated.

Applicable data types: All data types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Arithmetic operation cannot be operated on the result of SAMPLE function
Must be used with Partition by tbname when it's used on a STable to force the result on each single timeline.

TAIL

SELECT TAIL(field_name, k, offset_val) FROM {tb_name | stb_name} [WHERE clause];

Description: The next k rows are returned after skipping the last offset_val rows, NULL values are not ignored. offset_val is optional parameter. When it's not specified, the last k rows are returned. When offset_val is used, the effect is same as order by ts desc LIMIT k OFFSET offset_val.

Parameter value range: k: [1,100] offset_val: [0,100].

Return value type: Same as the column being operated upon.

Applicable column types: All data types.

TOP

SELECT TOP(field_name, K) FROM { tb_name | stb_name } [WHERE clause];

Description: The greatest k values of a specific column in a table or STable. If a value has multiple occurrences in the column but counting all of them in will exceed the upper limit k, then a part of them will be returned randomly.

Return value type: Same as the column being operated upon.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations:

k must be in range [1,100].
The timestamp associated with the selected values are returned too.
Cannot be used with FILL.

UNIQUE

SELECT UNIQUE(field_name) FROM {tb_name | stb_name} [WHERE clause];

Description: The values that occur the first time in the specified column. The effect is similar to distinct keyword, but it can also be used to match tags or timestamp.

Return value type: Same as the column or tag being operated upon.

Applicable column types: All data types.

More explanations:

It can be used against table or STable, but can't be used together with time window, like interval, state_window or session_window .
Considering the number of result sets is unpredictable, it's suggested to limit the distinct values under 100,000 to control the memory usage, otherwise error will be returned.

Time-Series Specific Functions

TDengine provides a set of time-series specific functions to better meet the requirements in querying time-series data. In general databases, similar functionalities can only be achieved with much more complex syntax and much worse performance. TDengine provides these functionalities in builtin functions so that the burden on user side is minimized.

CSUM

    SELECT CSUM(field_name) FROM { tb_name | stb_name } [WHERE clause]

Description: The cumulative sum of each row for a specific column. The number of output rows is same as that of the input rows.

Return value type: BIGINT for signed integer input types; UNSIGNED BIGINT for unsigned integer input types; DOUBLE for floating point input types.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Inner query and Outer query.

More explanations:

Arithmetic operation cannot be performed on the result of csum function.
Can only be used with aggregate functions.
Partition by tbname must be used together on a STable to force the result on a single timeline.

DERIVATIVE

SELECT DERIVATIVE(field_name, time_interval, ignore_negative) FROM tb_name [WHERE clause];

Description: The derivative of a specific column. The time rage can be specified by parameter time_interval, the minimum allowed time range is 1 second (1s); the value of ignore_negative can be 0 or 1, 1 means negative values are ignored.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations:

The number of result rows is the number of total rows in the time range subtracted by one, no output for the first row.
It can be used together with PARTITION BY tbname against a STable.
Can be used together with selection of relative columns. E.g. select _rowts, DERIVATIVE() from.

DIFF

SELECT {DIFF(field_name, ignore_negative) | DIFF(field_name)} FROM tb_name [WHERE clause];

Description: The different of each row with its previous row for a specific column. ignore_negative can be specified as 0 or 1, the default value is 1 if it's not specified. 1 means negative values are ignored.

Return value type: Same as the column being operated upon.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations:

The number of result rows is the number of rows subtracted by one, no output for the first row.
It can be used on STable with PARTITION by tbname.
Can be used together with selection of relative columns. E.g. select _rowts, DIFF() from.

IRATE

SELECT IRATE(field_name) FROM tb_name WHERE clause;

Description: instantaneous rate on a specific column. The last two samples in the specified time range are used to calculate instantaneous rate. If the last sample value is smaller, then only the last sample value is used instead of the difference between the last two sample values.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations:

It can be used on stble with PARTITION BY, i.e. timelines generated by PARTITION BY tbname on a STable.

MAVG

    SELECT MAVG(field_name, K) FROM { tb_name | stb_name } [WHERE clause]

Description: The moving average of continuous k values of a specific column. If the number of input rows is less than k, nothing is returned. The applicable range of k is [1,1000].

Return value type: DOUBLE.

Applicable data types: Numeric types.

Applicable nested query: Inner query and Outer query.

Applicable table types: table, STable.

More explanations:

Arithmetic operation cannot be performed on the result of MAVG.
Cannot be used with aggregate functions.
Must be used with PARTITION BY tbname when it's used on a STable to force the result on each single timeline.

STATECOUNT

SELECT STATECOUNT(field_name, oper, val) FROM { tb_name | stb_name } [WHERE clause];

Description: The number of continuous rows satisfying the specified conditions for a specific column. If the specified condition is evaluated as true, the number is increased by 1; otherwise the number is reset to -1. If the input value is NULL, then the corresponding row is skipped.

Applicable parameter values:

oper : Can be one of "LT" (lower than), "GT" (greater than), "LE" (lower than or euqal to), "GE" (greater than or equal to), "NE" (not equal to), "EQ" (equal to).
val ： Numeric types.

Return value type: INTEGER.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Outer query only.

More explanations:

Must be used together with PARTITION BY tbname when it's used on a STable to force the result into each single timeline.
Cannot be used with window operation, like interval/state_window/session_window.

STATEDURATION

SELECT stateDuration(field_name, oper, val, unit) FROM { tb_name | stb_name } [WHERE clause];

Description: The length of time range in which all rows satisfy the specified condition for a specific column. The length for the first row that satisfies the condition is 0. Next, if the condition is evaluated as true for a row, the time interval between current row and its previous row is added up to the time range; otherwise the time range length is reset to -1. If the value of the column is NULL, the corresponding row is skipped.

Applicable parameter values:

oper : Can be one of "LT" (lower than), "GT" (greater than), "LE" (lower than or euqal to), "GE" (greater than or equal to), "NE" (not equal to), "EQ" (equal to).
val : Numeric types.
unit : The unit of time interval, can be: 1b(nanosecond), 1u(microsecond),1a(millisecond),1s(second),1m(minute),1h(hour),1d(day),1w(week). If not specified, default is same as the current database time precision in use.

Return value type: INTEGER.

Applicable data types: Numeric types.

Applicable table types: table, STable.

Applicable nested query: Outer query only.

More explanations:

Must be used together with PARTITION BY tbname when it's used on a STable to force the result into each single timeline.
Cannot be used with window operation, like interval/state_window/session_window.

TWA

SELECT TWA(field_name) FROM tb_name WHERE clause;

Description: Time weighted average on a specific column within a time range.

Return value type: DOUBLE.

Applicable column types: Numeric types.

Applicable table types: table, STable.

More explanations:

It can be used on stable with PARTITION BY, i.e. timelines generated by PARTITION BY tbname on a STable.

System Information Functions

DATABASE

SELECT DATABASE();

Description：Return the current database being used. If the user doesn't specify database when logon and doesn't use USE SQL command to switch the datbase, this function returns NULL.

CLIENT_VERSION

SELECT CLIENT_VERSION();

Description：Return the client version.

SERVER_VERSION

SELECT SERVER_VERSION();

Description：Returns the server version.

SERVER_STATUS

SELECT SERVER_VERSION();

Description：Returns the server's status.

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Single-Row Functions

Numeric Functions

ABS

ACOS

ASIN

ATAN

CEIL

COS

FLOOR

LOG

POW

ROUND

SIN

SQRT

TAN

String Functions

CHAR_LENGTH

CONCAT

CONCAT_WS

LENGTH

LOWER

LTRIM

RTRIM

SUBSTR

UPPER

Conversion Functions

CAST

TO_ISO8601

TO_JSON

TO_UNIXTIMESTAMP

DateTime Functions

NOW

TIMEDIFF

TIMETRUNCATE

TIMEZONE

TODAY

Aggregate Functions

APERCENTILE

AVG

COUNT

ELAPSED

LEASTSQUARES

SPREAD

STDDEV

SUM

HYPERLOGLOG

HISTOGRAM

PERCENTILE

Selector Functions

BOTTOM

FIRST

INTERP

LAST

LAST_ROW

MAX

MIN

MODE

SAMPLE

TAIL

TOP

UNIQUE

Time-Series Specific Functions

CSUM

DERIVATIVE

DIFF

IRATE

MAVG

STATECOUNT

STATEDURATION

TWA

System Information Functions

DATABASE

CLIENT_VERSION

SERVER_VERSION

SERVER_STATUS

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