The subject disclosure is directed towards technology by which an expression in a database engine is executed against stacks of data. Each instruction of the expression is evaluated against the data stacks until completed against each data stack, such as by iterating to execute an instruction through the data stacks before executing the next instruction. The data may be arranged in the data stacks (in memory) in various ways, such as to have each data stack contain the data of one database row, (e.g., with the data stack elements comprising column data. Data may be grouped, such as to put the data from different rows into the same data stack.