MySQL foreach loop | 易学教程

问题

I have to iterate each row in my table User in MySQL. I need to create a new row Address for each iteration in User with some conditions described below.

I have 3 tables:

User: id, stuff, id_person, email
Person: id, stuff, id_address
Address: id, email

I need to create a new row in Address if the User.id_person is NOT NULL and that person.id_address IS NULL. I have to create the row with the same email that User.email. I have to do that for each row in User.

I tried to use MySQL cursor's but I do not know how to use them very well.

How can I do that? Is there any other way instead of using cursor's for that?

Thanks in advance.

EDIT: I have just realized that I also have to update person.id_address with the id of the address' row I have just created.

回答1:

From what I can gather, the following should suffice, so long as the fields are what you have provided.

INSERT INTO Address (email)
  SELECT User.email
    FROM User JOIN person ON User.id_person = person.id
   WHERE person.id_address IS NULL
;

EDIT (with Cursor)

This should be pretty simple with a cursor, however I highly advise you familiarize yourself with these and the implications.

DROP PROCEDURE IF EXISTS _tmp_update_address;
DELIMITER $$
CREATE PROCEDURE _tmp_update_address()
BEGIN
   DECLARE cursor_List_isdone BOOLEAN DEFAULT FALSE;
   DECLARE cur_userId, cur_personId INT;
   DECLARE cur_email VARCHAR(250) DEFAULT '';

   DECLARE cursor_List CURSOR FOR 
      SELECT User.id, person.id_address, User.email
      FROM User JOIN person ON User.id_person = person.id
      WHERE person.id_address IS NULL
    ;

   DECLARE CONTINUE HANDLER FOR NOT FOUND SET cursor_List_isdone = TRUE;

   OPEN cursor_List;

   loop_List: LOOP
      FETCH cursor_List INTO cur_userId, cur_personId, cur_email;
      IF cursor_List_isdone THEN
         LEAVE loop_List;
      END IF;

      INSERT INTO Address (email) VALUES (cur_email);
      UPDATE person SET person.id_address = LAST_INSERT_ID()
         WHERE person.id = cur_personId;

   END LOOP loop_List;

   CLOSE cursor_List;
END

$$

DELIMITER ;

CALL _tmp_update_address();

回答2:

You don't want to use a cursor for this. Based on what you describe:

insert into address (address)
    select u.email
    from user u join
         person p
         on u.id_person = p.id;

来源：https://stackoverflow.com/questions/49239885/mysql-foreach-loop

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mysql

loops

cursor