# MetricDataQuery
The metric data to return. Also defines whether this call is returning data for one metric only, or whether it is performing a math expression on the values of returned metric statistics to create a new time series. A time series is a series of data points, each of which is associated with a timestamp.
You can use `MetricDataQuery` structures with a [PutScalingPolicy](https://docs.aws.amazon.com/autoscaling/ec2/APIReference/API_PutScalingPolicy.html) operation when you specify a [PredictiveScalingConfiguration](https://docs.aws.amazon.com/autoscaling/ec2/APIReference/API_PredictiveScalingConfiguration.html) in the request. Predictive scaling uses the time series data received from CloudWatch to understand how to schedule capacity based on your historical workload patterns.
You can call for a single metric or perform math expressions on multiple metrics. Any expressions used in a metric specification must eventually return a single time series.
For more information and examples, see [Advanced predictive scaling policy configurations using custom metrics](https://docs.aws.amazon.com/autoscaling/ec2/userguide/predictive-scaling-customized-metric-specification.html) in the *Amazon EC2 Auto Scaling User Guide*.
## Contents
** Id **
A short name that identifies the object's results in the response. This name must be unique among all `MetricDataQuery` objects specified for a single scaling policy. If you are performing math expressions on this set of data, this name represents that data and can serve as a variable in the mathematical expression. The valid characters are letters, numbers, and underscores. The first character must be a lowercase letter.
Type: String
Length Constraints: Minimum length of 1. Maximum length of 255.
Pattern: `[\u0020-\uD7FF\uE000-\uFFFD\uD800\uDC00-\uDBFF\uDFFF\r\n\t]*`
Required: Yes
** Expression **
The math expression to perform on the returned data, if this object is performing a math expression. This expression can use the `Id` of the other metrics to refer to those metrics, and can also use the `Id` of other expressions to use the result of those expressions.
Conditional: Within each `MetricDataQuery` object, you must specify either `Expression` or `MetricStat`, but not both.
Type: String
Length Constraints: Minimum length of 1. Maximum length of 1023.
Pattern: `[\u0020-\uD7FF\uE000-\uFFFD\uD800\uDC00-\uDBFF\uDFFF\r\n\t]*`
Required: No
** Label **
A human-readable label for this metric or expression. This is especially useful if this is a math expression, so that you know what the value represents.
Type: String
Length Constraints: Maximum length of 2047.
Pattern: `[\u0020-\uD7FF\uE000-\uFFFD\uD800\uDC00-\uDBFF\uDFFF\r\n\t]*`
Required: No
** MetricStat **
Information about the metric data to return.
Conditional: Within each `MetricDataQuery` object, you must specify either `Expression` or `MetricStat`, but not both.
Type: [MetricStat](API_MetricStat.md) object
Required: No
** ReturnData **
Indicates whether to return the timestamps and raw data values of this metric.
If you use any math expressions, specify `true` for this value for only the final math expression that the metric specification is based on. You must specify `false` for `ReturnData` for all the other metrics and expressions used in the metric specification.
If you are only retrieving metrics and not performing any math expressions, do not specify anything for `ReturnData`. This sets it to its default (`true`).
Type: Boolean
Required: No
## See Also
For more information about using this API in one of the language-specific AWS SDKs, see the following:
+ [AWS SDK for C\$1\$1](https://docs.aws.amazon.com/goto/SdkForCpp/autoscaling-2011-01-01/MetricDataQuery)
+ [AWS SDK for Java V2](https://docs.aws.amazon.com/goto/SdkForJavaV2/autoscaling-2011-01-01/MetricDataQuery)
+ [AWS SDK for Ruby V3](https://docs.aws.amazon.com/goto/SdkForRubyV3/autoscaling-2011-01-01/MetricDataQuery)