如何從一個表中選擇一列，從另一個表中選擇另一列

Question

試圖建立一個數據庫，其中有一個問題表和一個問題答案表。

如何選擇一個問題（來自poll_question）和答案（來自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。 它需要另一列來指示每個答案屬於哪個問題，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查找給定問題的答案：

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

輸出：

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

dbfiddle上的演示