1. A method for optimizing query execution, the method comprising: identifying, in a query execution plan compiled for a query, a plurality of target operators that includes an expression that computes a common value; for a first target operator of the plurality of target operators, modifying a row output of the first target operator to add a column for an evaluation result comprising the common value; for at least one second target operator of the plurality of target operators, modifying a row input of the second target operator to add a column for the evaluation result comprising the common value; after modifying the row output for the first target operator and the row input for at least the second target operator, executing the query according to the plurality of target operators; wherein during said executing, the evaluation result comprising the common value is shared by passing the evaluation result from the row output for the first target operator to the row input for the at least one second target operator; wherein the method is performed by one or more computing devices.