Question

String ag ="ALTER TABLE QUESTION"+
            "(ADD  FOREIGN KEY (a_status) REFERENCES ANSWER(a_status))";

                      stmt.executeUpdate(ag);

错误讯息： com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException：你有一个 SQL语法错误;查看与您的手册相对应的手册 MySQL服务器版本，用于在＆＃39; FOREIGN KEY附近使用正确的语法（a_status）REFERENCES ANSWER（a_status））＆＃39;在第1行

Answer 1

这应该是正确的。请参阅offical documentation：

String ag ="ALTER TABLE QUESTION ADD FOREIGN KEY (a_status) REFERENCES ANSWER(a_status)";

Answer 2

String ag ="ALTER TABLE QUESTION ADD CONSTRAINT (question_answer_ibfk1) FOREIGN KEY (a_status) REFERENCES ANSWER(a_status)";

一般

ALTER TABLE Child_tblName
ADD CONSTRAINT 'give any name to the foreign key generally I do Child_tblName_Parent_tblName_ibfk_number' FOREIGN KEY ('Child_tblName's Column') REFERENCES Parent_tblName('Parent_tblName's Column')

Answer 3

String ag ="ALTER TABLE QUESTION ADD CONSTRAINT (question_answer_fk1) FOREIGN KEY (a_status) REFERENCES ANSWER(a_status)";

此外，您还可以添加更多特定条件：

ON DELETE SET NULL / CASCADE
ON UPDATE SET NULL

什么是执行sql语法的正确语法？

3 个答案: