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在PostgreSQL裏，with子句提供了一種方法寫一個大的查詢中使用的輔助報表與查詢。它有助於打破復雜和大型查詢簡單易讀的形式。

1. 建表
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1. postgres=# create table tb9(id serial primary key,name character varying, parentid integer);
2. CREATE TABLE

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1. postgres=# \d tb9
2. Table "public.tb9"
3. Column | Type | Modifiers
4. ----------+-------------------+--------------------------------------------------
5. id | integer | not null default nextval(‘tb9_id_seq‘::regclass)
6. name | character varying |
7. parentid | integer |
8. Indexes:
9. "tb9_pkey" PRIMARY KEY, btree (id)

2. 插入測試數據
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1. postgres=# insert into tb9 values(generate_series(1,5),‘john‘,0);
2. INSERT 0 5
3. postgres=# insert into tb9 values(6,‘john1‘,1);
4. INSERT 0 1
5. postgres=# insert into tb9 values(7,‘john2‘,1);
6. INSERT 0 1
7. postgres=# insert into tb9 values(8,‘john11‘,6);
8. INSERT 0 1

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1. postgres=# select * from tb9;
2. id | name | parentid
3. ----+--------+----------
4. 1 | john | 0
5. 2 | john | 0
6. 3 | john | 0
7. 4 | john | 0
8. 5 | john | 0
9. 6 | john1 | 1
10. 7 | john2 | 1
11. 8 | john11 | 6
12. (8 rows)

3. with子句
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1. postgres=# with t as (select * from tb9 where parentid=1) select count(0) from t;
2. count
3. -------
4. 2
5. (1 row)

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1. postgres=# with t(a,b,c) as (select * from tb9 where parentid=1) select a,b,c from t;
2. a | b | c
3. ---+-------+---
4. 6 | john1 | 1
5. 7 | john2 | 1
6. (2 rows)

4. 多個with子句的結合使用
parentid=1的記錄的所有子記錄
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1. postgres=# with t1 as (select * from tb9),t2 as(select * from tb9 where parentid=1) select t1.* from t1,t2 where t2.id=t1.parentid;
2. id | name | parentid
3. ----+--------+----------
4. 8 | john11 | 6
5. (1 row)

5. 遞歸
id為1的記錄的所有子記錄
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1. postgres=# with recursive t as(select id,name,parentid from tb9 where id=1 union all select k.id,k.name,k.parentid from tb9 k,t where t.id=k.parentid) select * from t;
2. id | name | parentid
3. ----+--------+----------
4. 1 | john | 0
5. 6 | john1 | 1
6. 7 | john2 | 1
7. 8 | john11 | 6
8. 9 | john21 | 7
9. (5 rows)

轉自 http://blog.csdn.net/luojinbai/article/details/44015581

postgresql with遞歸