column_ifexists()column_ifexists()

• 04/07/2021
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采用列名作为字符串和默认值。Takes a column name as a string and a default value. 返回对列的引用（如果存在），否则返回默认值。Returns a reference to the column if it exists, otherwise - returns the default value.

语法Syntax

column_ifexists(columnName, defaultValue)column_ifexists(columnName, defaultValue)

参数Arguments

• columnName：列的名称columnName: The name of the column
• defaultValue：在使用函数的上下文中不存在列时要使用的值。defaultValue: The value to use if the column doesn't exist in the context that the function was used in. 此值可以是任何标量表达式（例如，对另一列的引用）。This value can be any scalar expression (e.g. a reference to another column).

返回Returns

如果“columnName”存在，则使用它引用的列。If columnName exists, then the column it refers to. 否则使用“defaultValue”。Otherwise - defaultValue.

示例Examples

.create function with (docstring = "Wraps a table query that allows querying the table even if columnName doesn't exist ", folder="My Functions")
ColumnOrDefault(tableName:string, columnName:string)
{
    // There's no column "Capital" in "StormEvents", therefore, the State column will be used instead
    table(tableName) | project column_ifexists(columnName, State)
}


ColumnOrDefault("StormEvents", "Capital");