The impressions you've received on the Search Network divided by the estimated number of impressions you were eligible to receive. A percentage returned as "xx.xx%", or the special value "< 10%". To prevent calculation accuracy issues, fields whose data type is Double can be used only with the following operators in predicates: LESS_THAN or GREATER_THAN. This is also true for AWQL: Only the operators < and > are allowed in the WHERE clause.
You know, we can't aggregate percent values, but mb we can recieve two metrics, which you are using to calculate this metric "SearchImpressionShare" into Google Adwords UI?
Thank you,
Roman