MySQL CASE的INSERT INTO SELECT语句

Question

I am currently trying to insert multiple rows (three) of data into my database using one INSERT statement?

INSERT INTO dvd_price
( SELECT
, (SELECT max(dvd_price_id) + 1 FROM dvd_price) --dvd_price_id
, d.dvd_id                                      --dvd_id
, 2                                             --rental amount
, '1-day'                                       --time rented for
FROM dvd d);

The above will insert it once for 1-day ; I'd like to have the same statement also insert the data for 2-day and 3-day , with corresponding values ( 2 incremented once for each subsequent insert) for the rental amount.

Answer 1

To begin with, you should not be attempting to retrieve the next insert id by calling MAX(dvd_price_id) + 1 . That is not immune to race conditions, and can potentially cause problems as it is not reliable. If you do not have an AUTO_INCREMENT on dvd_price_id already, you are advised to add one and let the RDBMS handle the increment for you.

ALTER TABLE dvd_price MODIFY dvd_price_id INT NOT NULL PRIMARY KEY AUTO_INCREMENT;

Now, you don't need to worry about the dvd_price_id at all in the INSERT . To get all three values for 1-day, 2-day, 3-day you may create a cartesian product by joining against a list of those static values. That will result in one each of the day values for every row currently in the table.

INSERT INTO dvd_price (dvd_id, rental_amount, time_rented_for)
  SELECT
    dvd_id,
    2 AS rental_amount,
    rental_period
  FROM
    dvd
    /* join a subquery which creates a list of 'N-day' strings using
       SELECT 'value' UNION SELECT 'value'.....
       With no ON clause, it will do this for every row in `dvd`
     */
    CROSS JOIN (
      SELECT '1-day' AS rental_period 
      UNION SELECT '2-day' AS rental_period
      UNION SELECT '3-day' AS rental_period
  ) rental_periods

Test this first using only the SELECT portion of the query, without the INSERT .

Here is a demonstration of how it works: http://sqlfiddle.com/#!2/a0862/1