4.2还书 条件 读者表 reader code name address 199304034 first address 199304035 second address2 199304036 third address3 图书表 book cod tatus firstbook secondbook thirdbook fourthbook 3456789012 fifthbook sixthbook seventhbook eighthbook ninthbook s1111111111211 eleventhbook twelfthbook 20 Twentithbook Twentififthbook 0 借书记录表 book_codereader_code out_date 199304035 2000/6/10 789 199304035 2000/5/31 199304035 2000/6/10 199304035 2000/5/31 10 199304035 2000/6/10 12 199304036 2000/6/15 199304034 2000/5/21 199304034 2000/6/30 2345 199304034 2000/6/30 199304034 2000/8/21 199304034 2000/6/1 199304036 2000/6/10 用户输入 1)1(图书书号)4.2 还书 条件： 读者表 reader_code name address 199304034 first address1 199304035 second address2 199304036 third address3 图书表 book_code book_name status 1 firstbook 1 2 secondbook 1 3 thirdbook 1 4 fourthbook 1 5 fifthbook 1 6 sixthbook 1 7 seventhbook 1 8 eighthbook 1 9 ninthbook 1 10 tenthbook 1 11 eleventhbook 2 12 twelfthbook 1 20 Twentithbook 1 25 Twentififthbook 0 借书记录表 book_code reader_code out_date 6 199304035 2000/6/10 7 199304035 2000/5/31 8 199304035 2000/6/10 9 199304035 2000/5/31 10 199304035 2000/6/10 12 199304036 2000/6/15 1 199304034 2000/5/21 2 199304034 2000/6/30 3 199304034 2000/6/30 4 199304034 2000/8/21 5 199304034 2000/6/1 20 199304036 2000/6/10 用户输入： 1) 1(图书书号)