KADB行列转换

create table row2col(name varchar(20),subject varchar(20),grade varchar(10));

insert into row2col SELECT 'Tim' name, '数学' subject, 'A' grade

UNION

SELECT 'Tim' name, '英语' subject, 'B' grade

UNION

SELECT 'Tim' name, '语文' subject, null grade

UNION

SELECT 'Tom' name, '数学' subject, 'B' grade

UNION

SELECT 'Tom' name, '英语' subject, 'D' grade

UNION

SELECT 'Tom' name, '语文' subject, 'B' grade;

行转列:

select t.name,t.grades[1] 数学,t.grades[2] 英语,t.grades[3] 语文 from(

SELECT

t.name,

array_agg(t.grade order by t.subject) grades

FROM row2col t group by t.name)t;

name | 数学 | 英语 | 语文

------+------+------+------

Tim | A | B |

Tom | B | D | B

列转行:

select name,unnest(array['数学','英语','语文']),unnest(array[数学,英语,语文]) from (select t.name,t.grades[1] 数学,t.grades[2] 英语,t.grades[3] 语文 from(

SELECT

t.name,

array_agg(t.grade order by t.subject) grades

FROM row2col t group by t.name)t

)a;

name | unnest | unnest

------+--------+--------

Tim | 数学 | A

Tim | 英语 | B

Tim | 语文 |

Tom | 数学 | B

Tom | 英语 | D

Tom | 语文 | B

2、递归的实现方式

CREATE TABLE employees (

employee_id serial PRIMARY KEY,

full_name VARCHAR NOT NULL,

manager_id INT

);

INSERT INTO employees (

employee_id,

full_name,

manager_id

)

VALUES

(1, 'Michael North', NULL),

(2, 'Megan Berry', 1),

(3, 'Sarah Berry', 1),

(4, 'Zoe Black', 1),

(5, 'Tim James', 1),

(6, 'Bella Tucker', 2),

(7, 'Ryan Metcalfe', 2),

(8, 'Max Mills', 2),

(9, 'Benjamin Glover', 2),

(10, 'Carolyn Henderson', 3),

(11, 'Nicola Kelly', 3),

(12, 'Alexandra Climo', 3),

(13, 'Dominic King', 3),

(14, 'Leonard Gray', 4),

(15, 'Eric Rampling', 4),

(16, 'Piers Paige', 7),

(17, 'Ryan Henderson', 7),

(18, 'Frank Tucker', 8),

(19, 'Nathan Ferguson', 8),

(20, 'Kevin Rampling', 8);

返回id为2的经理的所有下属

WITH RECURSIVE subordinates AS (

SELECT

employee_id,

manager_id,

full_name

FROM

employees

WHERE

employee_id = 2

UNION

SELECT

e.employee_id,

e.manager_id,

e.full_name

FROM

employees e

INNER JOIN subordinates s ON s.employee_id = e.manager_id

) SELECT

*

FROM

subordinates;

employee_id | manager_id | full_name

-------------+------------+-----------------

2 | 1 | Megan Berry

9 | 2 | Benjamin Glover

8 | 2 | Max Mills

7 | 2 | Ryan Metcalfe

6 | 2 | Bella Tucker

19 | 8 | Nathan Ferguson

18 | 8 | Frank Tucker

20 | 8 | Kevin Rampling

16 | 7 | Piers Paige

17 | 7 | Ryan Henderson

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