query-optimized - sql优化

对以下三个语句进行优化

SELECT [ ENAME = 'Mary' & DNAME = 'Research' ] ( EMPLOYEE JOIN DEPARTMENT )

查询树如下：

优化后如下：

PROJECTION [ BDATE ] ( SELECT [ ENAME = 'John' & DNAME = 'Research' ] ( EMPLOYEE JOIN DEPARTMENT ) )

请查看tree2*xx.pdf

SELECT [ ESSN = '01' ] ( PROJECTION [ ESSN , PNAME ] ( WORKS_ON JOIN PROJECT ) )

请查看tree3xx.pdf