**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 plus the associated timestamp
**Return value type**: Same as the column being operated
**Applicable data types**: Any data type except for tags of STable
**Applicable data types**: Any data type
**Applicable nested query**: Inner query and Outer query
**Applicable table types**: standard tables and supertables
**More explanations**:
- This function cannot be used in expression calculation.
### TAIL
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@@ -1054,11 +1050,11 @@ TOP(expr, k)
UNIQUE(expr)
```
**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. The first occurrence of a timestamp or tag is used.
**Description**: The values that occur the first time in the specified column. The effect is similar to `distinct` keyword.
**Return value type**:Same as the data type of the column being operated upon
**Applicable column types**: Any data types except for timestamp