根据列值过滤或分离 SQL 查询

Question

我有一个查询要从电路中获取练习列表：

SELECT * 
FROM workouts
INNER JOIN circuits ON workouts.id = circuits.workout_id
INNER JOIN circuit_steps ON circuits.id = circuit_steps.circuit_id
INNER JOIN exercises ON exercises.id = circuit_steps.exercise_id
WHERE workouts.id = ${req.params.id}

当前结果是这个（为简洁起见的基本字段）

[
  {
    name: "Push Up",
    circuit_id: 1
  },
  {
    name: "Bicep Curl",
    circuit_id: 1
  },
  {
    name: "Squat",
    circuit_id: 2
  },
  {
    name: "Walk out",
    circuit_id: 2
  }
]

我希望能够通过GROUPcircuit_steps.circuit_id 得到结果所以结果是这样的：

[
  [
    { name: 'Push Up', circuit_id: 1},
    { name: 'Bicep Curl', circuit_id: 1},
  ],
  [
    { name: 'Squat', circuit_id: 2},
    { name: 'Walk Out', circuit_id: 2},
  ],
]

Answer 1

你可以使用string_agg():

SELECT cs.circuit_id, string_agg(e.name, ',') as execise_names
FROM workouts w INNER JOIN
     circuits c
     ON w.id = c.workout_id INNER JOIN
     circuit_steps cs
     ON c.id = cs.circuit_id INNER JOIN
     exercises e
     ON e.id = cs.exercise_id
WHERE workouts.id=${req.params.id}
GROUP BY cs.circuit_id