cols desc
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@ -2125,6 +2125,27 @@ UNIQUE(expr)
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**Applicable to**: Tables and supertables.
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### COLS
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```sql
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COLS(select_function(expr), output_expr1, [, output_expr2] ... )
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```
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**Function Description**: On the data row where the execution result of function func (expr) is located, execute the expression output_expr1, [, output_expr2], return its result, and the result of func (expr) is not output.
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**Return Data Type**: Returns multiple columns of data, and the data type of each column is the type of the result returned by the corresponding expression.
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**Applicable Data Types**: All type fields.
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**Applicable to**: Tables and Super Tables.
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**Usage Instructions**:
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- Func function type: must be a single-line selection function (output result is a single-line selection function, for example, last is a single-line selection function, but top is a multi-line selection function).
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- The result of the parameter func is not returned. If you want to output the result of func, you need to add the corresponding output_expr parameter to the letter.
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- When there is only one column in the output, you can set an alias for the function. For example, you can do it like this: "select cols(first (ts), c1) as c11 from ...".
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- Output one or more columns, and you can set an alias for each output column of the function. For example, you can do it like this: "select (first (ts), c1 as c11, c2 as c22) from ...".
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## Time-Series Specific Functions
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Time-Series specific functions are tailor-made by TDengine to meet the query scenarios of time-series data. In general databases, implementing similar functionalities usually requires complex query syntax and is inefficient. TDengine has built these functionalities into functions, greatly reducing the user's cost of use.
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@ -2051,6 +2051,26 @@ UNIQUE(expr)
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**适用于**: 表和超级表。
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### COLS
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```sql
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COLS(select_function(expr), output_expr1, [, output_expr2] ... )
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```
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**功能说明**:在选择函数 func(expr) 执行结果所在数据行上,执行表达式 output_expr1, [,output_expr2],返回其结果,func(expr)结果不输出.
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**返回数据类型**:返回多列数据,每列数据类型为对应表达式返回结果的类型。
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**适用数据类型**:全部类型字段。
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**适用于**:表和超级表。
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**使用说明:**
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- func 函数类型:必须是单行选择函数(输出结果为一行的选择函数,例如 last 是单行选择函数, 但 top 是多行选择函数)。
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- 注意, 参数 func 的结果并没有返回,如需输出 func 结果,需要在 cols 中加上相应的 output_expr 参数。
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- 输出只有一列时,可以对 cols 函数设置别名。例如: "select cols(first(ts), c1) as c11 from ..."
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- 输出一列或者多列,可以对 cols 函数的每个输出列设置命名。例如: "select cols(first(ts), c1 as c11, c2 as c22)"
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## 时序数据特有函数
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