@@ -22,8 +22,8 @@ SELECT COUNT([*|field_name]) FROM tb_name [WHERE clause];
**More explanation**:
- Wildcard (\*) can be used to represent all columns, it's used to get the number of all rows
- The number of non-NULL values will be returned if this function is used on a specific column
- Wildcard (\*) is used to represent all columns. The `COUNT` function is used to 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.
**Examples**:
...
...
@@ -87,7 +87,7 @@ SELECT TWA(field_name) FROM tb_name WHERE clause;
**More explanations**:
-From version 2.1.3.0, function TWA can be used on stable with `GROUP BY`, i.e. timelines generated by `GROUP BY tbname` on a STable.
-Since version 2.1.3.0, function TWA can be used on stable with `GROUP BY`, i.e. timelines generated by `GROUP BY tbname` on a STable.
### IRATE
...
...
@@ -105,7 +105,7 @@ SELECT IRATE(field_name) FROM tb_name WHERE clause;
**More explanations**:
-From version 2.1.3.0, function IRATE can be used on stble with `GROUP BY`, i.e. timelines generated by `GROUP BY tbname` on a STable.
-Since version 2.1.3.0, function IRATE can be used on stble with `GROUP BY`, i.e. timelines generated by `GROUP BY tbname` on a STable.
### SUM
...
...
@@ -149,7 +149,7 @@ SELECT STDDEV(field_name) FROM tb_name [WHERE clause];
**Applicable column types**: Data types except for timestamp, binary, nchar and bool
**Applicable table types**: table, STable (starting from version 2.0.15.1)
**Applicable table types**: table, STable (since version 2.0.15.1)
**Examples**:
...
...
@@ -193,13 +193,13 @@ 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. It can't be used on timestamp column or tags.
**Return value type**:Same as the data type of the column being operated
**Return value type**:Same as the data type of the column being operated upon
**Applicable column types**:Data types except for timestamp
**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.
**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.
**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
**Return value type**: Same as the column being operated upon
**Applicable column types**: Data types except for timestamp, binary, nchar and bool
**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
**Return value type**: Same as the column being operated upon
**Applicable column types**: Data types except for timestamp, binary, nchar and bool
-`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, `where` can be used to filter the original data. If no `where` condition is specified then all original data is the input.
- 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.
taos> SELECT INTERP(current) FROM t1 where ts >= '2017-07-14 17:00:00' and ts <= '2017-07-14 20:00:00' RANGE('2017-7-14 18:00:00','2017-7-14 19:00:00') EVERY(5s) FILL(LINEAR);
```
### INTERP [Prior to version 2.3.1]
### INTERP [Since version 2.0.15.0]
```
SELECT INTERP(field_name) FROM { tb_name | stb_name } WHERE ts='timestamp' [FILL ({ VALUE | PREV | NULL | LINEAR | NEXT})];
...
...
@@ -640,7 +640,7 @@ SELECT INTERP(field_name) FROM { tb_name | stb_name } WHERE ts='timestamp' [FILL
**Description**: The value of a specific column that matches the specified time slice
**Return value type**: Same as the column being operated
**Return value type**: Same as the column being operated upon
**Applicable column types**: Numeric data type
...
...
@@ -648,7 +648,6 @@ SELECT INTERP(field_name) FROM { tb_name | stb_name } WHERE ts='timestamp' [FILL
**More explanations**:
- It can be used from version 2.0.15.0
- Time slice must be specified. If there is no data matching the specified time slice, interpolation is performed based on `FILL` parameter. Conditions such as tags or `tbname` can be used `Where` clause can be used to filter data.
- The timestamp specified must be within the time range of the data rows of the table or STable. If it is beyond the valid time range, nothing is returned even with `FILL` parameter.
-`INTERP` can be used to query only single time point once. `INTERP` can be used with `EVERY` to get the interpolation value every time interval.
**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
**Return value type**: Same as the column or tag being operated upon
**Applicable column types**: Any data types except for timestamp
**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
**Return value type**: Same as the column being operated upon
**Applicable column types**: Data types except for timestamp, binary, nchar and bool
