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Postgresql join 操作
1. 建表&插入数据
2. inner join
3. full outer join
4. left outer join
5. 参考
1. 建表&插入数据
创建表 test_a, test_b
shop_5> CREATE TABLE test_a(id serial, name VARCHAR(32));
CREATE TABLE
Time: 0.019s
shop_5> \d test_a;
+----------+-----------------------+------------------------------------------------------+
| Column | Type | Modifiers |
|----------+-----------------------+------------------------------------------------------|
| id | integer | not null default nextval('test_a_id_seq'::regclass) |
| name | character varying(32) | |
+----------+-----------------------+------------------------------------------------------+
Time: 0.006s
shop_5> INSERT INTO test_a(name) VALUES ('a'),('b'),('c'),('d');
INSERT 0 4
Time: 0.011s
shop_5> SELECT * from test_a;
+------+--------+
| id | name |
|------+--------|
| 1 | a |
| 2 | b |
| 3 | c |
| 4 | d |
+------+--------+
SELECT 4
Time: 0.001s
shop_5> CREATE TABLE test_b(id serial, name VARCHAR(32));
CREATE TABLE
Time: 0.012s
shop_5> \d test_b;
+----------+-----------------------+------------------------------------------------------+
| Column | Type | Modifiers |
|----------+-----------------------+------------------------------------------------------|
| id | integer | not null default nextval('test_b_id_seq'::regclass) |
| name | character varying(32) | |
+----------+-----------------------+------------------------------------------------------+
Time: 0.003s
shop_5> INSERT INTO test_b(name) VALUES ('c'),('d'),('e'),('f');
INSERT 0 4
Time: 0.009s
shop_5> SELECT * from test_b;
+------+--------+
| id | name |
|------+--------|
| 1 | c |
| 2 | d |
| 3 | e |
| 4 | f |
+------+--------+
SELECT 4
Time: 0.002s2. inner join
内联合（inner join）只生成同时匹配表A和表B的记录集。
shop_5> SELECT * from test_a a INNER JOIN test_b b on a.name = b.name;
+------+--------+------+--------+
| id | name | id | name |
|------+--------+------+--------|
| 3 | c | 1 | c |
| 4 | d | 2 | d |
+------+--------+------+--------+
SELECT 2
Time: 0.001s3. full outer join
全外联合（full outer join）生成表A和表B里的记录全集，包括两边都匹配的记录。如果有一边没有匹配的，缺失的这一边为null。
shop_5> SELECT * from test_a a FULL OUTER JOIN test_b b on a.name = b.name;
+--------+--------+--------+--------+
| id | name | id | name |
|--------+--------+--------+--------|
| 1 | a | | |
| 2 | b | | |
| 3 | c | 1 | c |
| 4 | d | 2 | d |
| | | 3 | e |
| | | 4 | f |
+--------+--------+--------+--------+
SELECT 6
Time: 0.001s 4. left outer join
左外联合（left outer join）生成表A的所有记录，包括在表B里匹配的记录。如果没有匹配的，右边将是null。
shop_5> SELECT * from test_a a LEFT OUTER JOIN test_b b on a.name = b.name;
+------+--------+--------+--------+
| id | name | id | name |
|------+--------+--------+--------|
| 1 | a | | |
| 2 | b | | |
| 3 | c | 1 | c |
| 4 | d | 2 | d |
+------+--------+--------+--------+
SELECT 4
Time: 0.003s 5. 参考
http://francs3.blog.163.com/blog/static/405767272012101011193243/
http://www.yiibai.com/html/postgresql/2013/080569.html
http://blog.jobbole.com/40443/