Question

我有以下查询将数据插入多对多连接表

INSERT INTO playlist_genre(playlist_id, genre_id)
VALUES  (${playlistId}, ${genre1Id}),
        (${playlistId}, ${genre2Id}),
        (${playlistId}, ${genre3Id})
);

然而，我遇到的问题是，用户不需要值genre2Id和genre3Id，因此可以是INTEGER或NULL

我试图找到一种方法来编写同样的查询，但只有在存在值时才会插入。两列都有NOT NULL个约束。

修改：

这是我的播放列表

class Playlist {
  constructor(playlist) {
    // required fields
    this.title = playlist.title;
    this.playlistType = playlist.playlistType;
    this.userId = playlist.userId;
    this.numberOfTracks = playlist.numberOfTracks;
    this.lengthInSeconds = playlist.lengthInSeconds;
    this.genre1Id = playlist.genre1Id;
    // not required fields
    this.genre2Id = playlist.genre2Id || null;
    this.genre3Id = playlist.genre3Id || null;
    this.description = playlist.description || null;
    this.releaseDate = playlist.releaseDate || null;
  }

  save() {
    return new Promise((resolve, reject) => {
      db.one(sqlCreatePlaylist, this)
        .then((insertedPlaylist) => {
          // Here is where i want to use insertedPlaylist's id 
          // to insert data into 'playlist_genre' table
          resolve(insertedPlaylist);
        })
        .catch(error => reject(error));
    });
  }

这是sqlCreatePlaylist的样子

INSERT INTO playlists(
  user_id,
  title,
  playlist_type,
  number_of_tracks,
  duration,
  description,
  release_date
)
VALUES(
  ${userId},
  ${title},
  ${playlistType},
  ${numberOfTracks},
  ${lengthInSeconds},
  ${description},
  ${releaseDate}
)
RETURNING *;

Answer 1

仅插入非空值：

insert into playlist_genre (playlist_id, genre_id)
select playlist_id, genre_id
from (values
    (${playlistid}, ${genre1id}),
    (${playlistid}, ${genre2id}),
    (${playlistid}, ${genre3id})
) s (playlist_id, genre_id)
where genre_id is not null

如何避免在postgres数据库中插入空值

1 个答案: