需要有關SQL查詢的幫助

Question

當前查詢

SELECT *
FROM employee AS E
INNER JOIN credential AS C ON (C.id = E.credentialId)
LEFT JOIN person AS P ON (C.personId = P.id)

我想修改此查詢，以便僅選擇同時具有登錄名1和登錄名2（loginrole.id）的員工/憑證。

相關表

loginrole
    id
    name
credential_has_loginrole
    id
    credentialId
    loginroleId

Answer 1

您可以加入子查詢，該子查詢將返回具有兩個登錄角色的憑據ID。

SELECT E.*, C.*, P.*
FROM employee AS E
  INNER JOIN (
      SELECT credentialId
      FROM credential_has_loginrole
      WHERE loginroleId IN (1,2)
      GROUP BY credentialId
      HAVING COUNT(DISTINCT loginroleId) = 2
    ) g ON E.credentialId = g.credentialId
  INNER JOIN credential AS C ON (C.id = E.credentialId)
  LEFT JOIN person AS P ON (C.personId = P.id)

更新 ：根據評論，查找具有以下任一項的員工：

SELECT E.*, C.*, P.*
FROM employee AS E
  INNER JOIN (
      SELECT credentialId
      FROM credential_has_loginrole
      WHERE loginroleId IN (1,2)
      GROUP BY credentialId
    ) g ON E.credentialId = g.credentialId
  INNER JOIN credential AS C ON (C.id = E.credentialId)
  LEFT JOIN person AS P ON (C.personId = P.id)

另外，您可以將JOIN與DISTINCT一起使用：

SELECT DISTINCT E.*, C.*, P.*
FROM employee AS E
  INNER JOIN credential AS C ON (C.id = E.credentialId)
  INNER JOIN credential_has_loginrole chr
    ON E.credentialId = chr.credentialId
      AND chr.loginroleId IN (1,2)
  LEFT JOIN person AS P ON (C.personId = P.id)

Answer 2

Scrum Meister的答案是正確的。 您也可以使用2個連接樹：

    SELECT *
    FROM employee AS E
    INNER JOIN credential AS c 
        INNER JOIN credential_has_loginrole chl0 ON (c0.id=chl0.credentialId AND chl0.loginroleId=1)
        INNER JOIN credential_has_loginrole chl1 ON (c0.id=chl1.credentialId AND chl1.loginroleId=2)
    ON (c.id = E.credentialId)