rel-ops.txt

来自「answer to sd7 Exercise1」· 文本 代码 · 共 14 行

ANALYSE:
  Because title and price belong to the BOOK table,and the searching 
condition is in the PUBLISHER table.
(1) Selecting Title and Price refer to PublisherID,
    which  were selected from PUBLISHER TABLE where the 
  Publisher's name equals "Addison Wesley", from  the BOOK TABLE.
  Project the selected Title and Price in a unique-table.

(2) Selecting Title and Price refer to the PublisherID,
    which were selected from PUBLISHER TABLE where 
 the Publisher's name equals "McGraw Hill", from  the BOOK TABLE.
 Projection the selected Title and Price in a unique-table.

(3) Joining the two projection.