Question

给出以下表结构：我需要在人类可读的平面文件中获取记录：

    CREATE  TABLE `formsfiles`.`Teams` (
  `ID` INT NOT NULL AUTO_INCREMENT ,
  `Name` VARCHAR(45) NULL ,
  PRIMARY KEY (`ID`) );


INSERT INTO `Teams` (`Name`) VALUES ('Sharks');
INSERT INTO `Teams` (`Name`) VALUES ('Jets');
INSERT INTO `Teams` (`Name`) VALUES ('Fish');
INSERT INTO `Teams` (`Name`) VALUES ('Dodgers');
INSERT INTO `Teams` (`Name`) VALUES ('Pigs');

CREATE  TABLE `Players` (
  `ID` INT NOT NULL AUTO_INCREMENT ,
  `Name` VARCHAR(45) NULL ,
  `Team_ID` INT NULL ,
  PRIMARY KEY (`ID`) );

INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Jim', '1');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Tom', '1');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Harry', '2');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Dave', '2');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Tim', '3');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Trey', '4');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Jay', '4');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Steve', '4');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Ziggy', '5');
INSERT INTO `Players` (`Name`, `Team_ID`) VALUES ('Chris', '4');

我想要玩家表格的输出：

    ID     Name     Team_ID     Team
1      Jim      1           Sharks

2      Tom      1           Sharks

3      Harry    2           Jets

4      Dave     2           Jets

我认为这是一个简单的连接，但不是一个SQL人我踩着他的语法，似乎无法得到它。（请原谅问题的基本性质）

Answer 1

select p.ID, p.Name, t.ID as Team_ID, t.Name as Team
from formsfiles.Teams t inner join Players p on p.Team_ID = t.ID

Answer 2

基本上这是你追求的问题：

 dat <- structure(list(TEAM1 = c("A", "I", "P", "S", "S", "W", "A", "A", 
 "E"), TEAM2 = c("P", "S", "S", "I", "P", "P", "E", "S", "A"), 
 WINNER = c("A", "I", "S", "I", "P", "W", "A", "S", "E")),
 .Names =   c("TEAM1", 
 "TEAM2", "WINNER"), class = "data.frame", row.names = c(NA, -9L))

但是你应该真正阅读一些关于连接和sql的内容，这是非常有用的东西。

Answer 3

// returns all elements from arr1, that doesn't have matching ID in arr2
function except(arr1, arr2, propertyName='ID') {
    let exceptIds = new Set(arr2.map(el=>el[propertyName])); // get set of all IDs in array2
    return arr1.filter(el=>!exceptIds.has(el[propertyName]));
}

在mySql中简单加入理解 - 记录到平面文件

3 个答案: