一些几个经典的postgresql的sql语句

1.强制类型转换:
1.1. select created_at::date from user
1.2. select created_at::varchar from user
1.3 select cast(created_at as date) from user

2.伴随语句查询
2.1. with tmp as (select name,age from user),
tmp2 as （select sal,join_at from company）
select * from user_detail,tmp,tmp2 where user_age = tmp.age [

3.批量插入
3.1 insert into user(name,age) select name,age from account

4.内嵌条件语句
4.1 select case when t.result=‘success’ then 0 else 1 end from table_result as t

5.无返回值且可以重复运行的函数

--将account中在t这一天时间里新增的用户同步到user表里
create function synchronize_user(t date) returns void as 
$$
begin
delete from user where created=t;
insert into user(name,age) select name,age from account where created=t;
end;      
$$
LANGUAGE 'plpgsql' VOLATILE;

调用方式:

select synchronize_user('2018-08-17')

6.函数名重载

--将account中所有的用户同步到user表里,可以与5并存
create function synchronize_user() returns void as 
$$
begin
delete from user;
insert into user(name,age) select name,age from account;
end;      
$$
LANGUAGE 'plpgsql' VOLATILE;

调用方法:

select synchronize_user()

7.创建视图

create view tmp as 
  (
	select user_id,created,sum(total_money) 
	from orders 
	group by user_id,created 
  )

使用时：

select * from tmp where created='2018-09-02'

8.自定义递增序列及使

CREATE SEQUENCE 
index_sequence 
START WITH 13 --自定义自增长开始的值 
INCREMENT BY 1 --每次递增多少 
NO MINVALUE 
NO MAXVALUE 
CACHE 1

create table t(
id integer default nextval('index_sequence')
)

9.伴随语句与批量插入同时进行

with tmp as (
select user_id,sum(money) as money from users group by user_id
)
insert into money_analysis(user_id,money) select * from tmp

10.左右全连接出现的null处理补0或者补’’

--student的id比class_student的student的id多，造成了一些补充数据null
--对fee补0，对introduction补''
select student.id,
       case when fee is null then 0 else fee end ,
       case when introduction is null then '' else introduction
from student left join class_student on student.id = class_student.student_id

返回table的函数

/*注意点
12. table声明的参数数量和类型要和内部的select一致,但取名不能一致，不然会冲突。
13. 调用时，对于插入修改删除类型的可以使用select fun(),但是对于select最好使用select * from fun()，因为select fun()对select查询会返回出raw message，比如(1,'fw',9)而不是 user_id|name|age \n 1|'fw'|9
*/
create function find_master() returns table(nm varchar,uid integer,ag integer) as
$$
begin
return query
(
 select name,user_id,age from tuser
);
end;
$$
language 'plpgsql' volatile;

使用时:

select * from find_master()
-- 千万不要使用,这是数据流
select find_master()

逻辑取反
并没有查到官方的取反操作,只有自己写了


create or replace function getnot(arg boolean) returns boolean as
$BODY$
begin
	if arg=true then
		return false;
	else 
		return true;
	end if;
end;
$BODY$
language 'plpgsql' volatile;

使用时:

-- 选出用户表里，排除掉 id >5 且age < 3 的用户
select * from tuser where getnot(id>5 and age<3)

一些几个经典的postgresql的sql语句

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