Question

试图建立一个数据库，该数据库具有一个问题表和一个问题答案表。

如何选择一个问题（来自poll_question）和答案（来自poll_answer）？

CREATE TABLE poll_question(Id_question int primary key not null, question varchar(60));

CREATE TABLE poll_answer(Id_answer int primary key not null, answer varchar(100));

INSERT INTO poll_question(Id_questao, questao)
VALUES(1,"What kind of paper is allowed in tommorows exam?");

INSERT INTO poll_answer(Id_answer,answer)
VALUES(1,"A4 squared sheet");

INSERT INTO poll_answer(Id_answer,answer)
VALUES(2,"A4 lined sheet");

Answer 1

您的poll_answer表不完整。它需要另一列来表明每个答案属于哪个问题，例如

CREATE TABLE poll_answer(Id_answer int primary key not null, Id_question int, answer varchar(100));
INSERT INTO poll_answer(Id_answer,Id_question,answer)
VALUES(1,1,"A4 squared sheet"),
(2,1,"A4 lined sheet");

然后，您可以使用JOIN找到给定问题的答案：

SELECT q.question, a.answer
FROM poll_question q
JOIN poll_answer a ON a.Id_question = q.Id_question

输出：

question                                            answer
What kind of paper is allowed in tommorows exam?    A4 squared sheet
What kind of paper is allowed in tommorows exam?    A4 lined sheet

Demo on dbfiddle

如何从一个表中选择一列，从另一个表中选择另一列

1 个答案: