MySQL - 遞歸查詢部門組織
Max.Bai
2019-11
0x00: 背景
項目需要查詢某個人所屬的部門,上級,上上上級部門,就是查到這個人所屬的部門路徑。
0x01: MySQL 代碼
SELECT id, dept_name, `level`, parent_dept_id
FROM (
SELECT
@r AS _id,
(SELECT @r := parent_dept_id FROM dept WHERE id = _id) AS parent_id,
@l := @l + 1 AS lvl
FROM
(SELECT @r := 3478, @l := 0) vars,
dept h
WHERE @r <> 0
) T1
JOIN dept T2
ON T1._id = T2.id
ORDER BY `level`;
代碼裏面的3478 就是這個人所屬的當前部門id,
查到結果:
0x02: 核心代碼理解
SELECT
@r AS _id,
(SELECT @r := parent_dept_id FROM dept WHERE id = _id) AS parent_id,
@l := @l + 1 AS lvl
FROM
(SELECT @r := 3478, @l := 0) vars,
dept h
WHERE @r <> 0
有2個變量
@r 就是部門id
@l 就是遞歸查詢的層數
首先給變量賦值
(SELECT @r := 3478, @l := 0) vars,
@r<>0 就是遞歸結束的條件,不然一直遞歸下去了
select 裏面的內容就是每次遞歸執行的內容,有3個部分:
1. 顯示當前@r 變量的值,就是這裏的當前部門id @r AS _id,
2. 以當前id查到父id,顯示父id,並把父id賦值給@r變量
(SELECT @r := parent_dept_id FROM dept WHERE id = _id) AS parent_id,
3. 層級加1 並顯示當前層級 @l := @l + 1 AS lvl
from 裏面是變量初始值,和部門表
where 裏面是停止循環的條件,這裏是當前部門id不等於0 的時候一直執行循環
0x03 查詢所有部門的所有上級部門id
SELECT
`dept_name`,
id AS id,
parent_dept_id AS PID,
levels AS Level,
CONCAT(paths,',',id) AS path
FROM
(
SELECT
`dept_name`,
id,
parent_dept_id,
@le :=
IF
(
parent_dept_id = 0,
0,
IF
(
LOCATE( CONCAT( '|', parent_dept_id, ':' ), @pathlevel ) > 0,
SUBSTRING_INDEX( SUBSTRING_INDEX( @pathlevel, CONCAT( '|', parent_dept_id, ':' ),- 1 ), '|', 1 ) + 1,
@le + 1
)
) levels,
@pathlevel := CONCAT( @pathlevel, '|', id, ':', @le, '|' ) pathlevel,
@pathnodes :=
IF
(
parent_dept_id = 0,
',0',
CONCAT_WS(
',',
IF
(
LOCATE( CONCAT( '|', parent_dept_id, ':' ), @pathall ) > 0,
SUBSTRING_INDEX( SUBSTRING_INDEX( @pathall, CONCAT( '|', parent_dept_id, ':' ),- 1 ), '|', 1 ),
@pathnodes
),
parent_dept_id
)
) paths,
@pathall := CONCAT( @pathall, '|', id, ':', @pathnodes, '|' ) pathall
FROM
dept,
( SELECT @le := 0, @pathlevel := '', @pathall := '', @pathnodes := '' ) vv
ORDER BY
parent_dept_id,
id
) src
ORDER BY
parent_dept_id;