PostgreSQL数据库-PL/PGSQL 使用学习

基本结构

create or replace function somefunc() 
returns varchar as 
$$
declare
   name varchar := 'wangzhen';
begin
   return name;
end   
$$ language plpgsql ；

$$作用

• 函数代码在function中实际上为一个字符串，代码1和代码2等价，但代码中字符串的单引号需要写两个进行转义。

-- 代码1
create or replace function somefunc() 
returns varchar as 
$$
declare
   name varchar := 'wangzhen';
begin
   return name;
end   
$$ language plpgsql ；

--代码2
create or replace function somefunc() 
returns varchar as 
'
declare
   name varchar := ''wangzhen'';
begin
   return name;
end   
' language plpgsql ;

• “美元符引用”书写字符串常量，使单引号、反斜线、$符等按照字面值进行解释，不需要写两个或在4个或着更多进行转义，代码3和代码4等价。

--代码3
create or replace function somefunc() 
returns varchar as 
$$
declare
   name varchar := 'wangzhen''blog';
begin
   return name;
end   
$$ language plpgsql ;

--代码4
create or replace function somefunc() 
returns varchar as 
$$
declare
   name varchar := $tag$wangzhen'blog$tag$;
begin
   return name;
end   
$$ language plpgsql ;

• $中间可以包含可选的标签，但是标签要成对出现，且大小写敏感。代码5和代码6和代码7等价。

--代码5
create or replace function somefunc() 
returns varchar as 
$body$
declare
   name varchar := $tag$wangzhen'blog$tag$;
begin
   return name;
end   
$body$ language plpgsql ;

--代码6
create or replace function somefunc() 
returns varchar as 
$func$
declare
   name varchar := $$wangzhen'blog$$;
begin
   return name;
end   
$func$ language plpgsql ;

--代码7
create or replace function somefunc() 
returns varchar as 
$$
declare
   name varchar := 'wangzhen''blog';
begin
   return name;
end   
$$ language plpgsql ;

代码块

• 块名可选，代码8和9等价

--代码8
create or replace function somefunc() 
returns varchar as
$$
<>
declare 
   name varchar := 'wangzhen';
begin
   return outblock.name;
end;        
$$ language plpgsql; 

--代码9
create or replace function somefunc() 
returns varchar as
$$
declare 
   name varchar := 'wangzhen';
begin
   return name;
end;        
$$ language plpgsql; 

• 块可嵌套，内层同名变量覆盖外层同名变量，可通过指定块名引用。

--代码10
create or replace function somefunc() 
returns varchar as
$$
<>
declare 
   name varchar := 'wangzhen';
begin
   <>
   declare 
      name varchar := 'xiaozhang';
   begin
      outblock.name = innerblock.name;
   end;   
   return outblock.name;
end;        
$$ language plpgsql; 

abase=# select somefunc();
 somefunc  
-----------
 xiaozhang

• 函数体是一个隐藏的块，块名是函数名。

--代码11
create or replace function somefunc(name varchar) 
returns varchar as
$$
<>
declare 
   name varchar := somefunc.name;
begin
   return outblock.name;
end;        
$$ language plpgsql; 

abase=# select somefunc('xiaoli');
 somefunc 
----------
 xiaoli
(1 row)

命名参数

• 在函数声明时直接命名参数

--代码12
create or replace function somefunc(newname varchar) 
returns varchar as
$$
declare 
   name varchar := newname;
begin
   return name;
end;        
$$ language plpgsql; 

• 使用别名和美元符号

--代码13
create or replace function somefunc(varchar,varchar) 
returns varchar as
$$
declare 
   newname alias for $1;
   name varchar := newname;
   name2 varchar := $2;
begin
   return name;
end;        
$$ language plpgsql; 

执行SQL

• 没有返回结果的SQL可以直接执行

--代码14
create or replace function somefunc2() 
returns void as
$$
begin
   create table test1 (n_id integer,c_mc varchar(300));
   insert into test1 (n_id,c_mc) values (1,'wangzhen');
end;        
$$ language plpgsql; 

• 不需要返回结果的select可以通过perform执行。perform替换select

--代码15
create or replace function somefunc3() 
returns void as
$$
begin
   perform * from test1;
end;        
$$ language plpgsql; 

--代码16
create or replace function somefunc3() 
returns void as
$$
begin
   perform somefunc();
   --perform 怎么处理with和其他复杂查询？
end;        
$$ language plpgsql; 

• 执行动态拼接SQL

--代码17
create or replace function somefunc3() 
returns void as
$$
declare
var_sql varchar := 'insert into test1 values (0,'||quote_literal('admin')||')';
begin
   execute var_sql;
   execute format('insert into %I values (%L,%L)','test1',2,'xiaoniu');
end;        
$$ language plpgsql; 

返回结果

返回结果分为返回标量（单行）和返回结果集合（多行）两种情况。

• 返回标量

-- 代码18
-- 返回单行int
create or replace function somefunc4()
returns int as
$$
begin
   return 100;
end   
$$ language plpgsql;

-- 代码19
-- 通过out参数返回
create or replace function somefunc4(out v1 integer) 
as
$$
begin
   v1 := 100;
end  
$$ language plpgsql;

-- 代码20
-- 返回单行record 复合类型
create or replace function somefunc4(id integer,mc varchar) 
returns record as
$$
declare 
   r record;
begin
   r := row(id,mc);
   return r;
end  
$$ language plpgsql;

• SETOF 作用

  返回结果集合（多行）时，需要使用SETOF指定

--代码21
--返回单列多行
create or replace function somefunc5()
returns setof int as
$$
declare
id int;
begin
   for id in select n_id from test1 
   loop
      return next id;
   end loop;
   return;  
end   
$$ language plpgsql;

结果：

abase=# select somefunc5();
 somefunc5 
-----------
         1
         1
         0
         0
         2
(5 rows)

• 返回结果集

-- 代码22
-- 通过out参数返回
-- returns setof record  可以省略
create or replace function somefunc6(out id integer,out name varchar)
returns setof record as 
$$
declare 
   r record;
begin
   for r in select n_id,c_mc from test1 
   loop
      id := r.n_id;
      name := r.c_mc;
      return next;
   end loop; 
end
$$ language plpgsql;

结果：

abase=# select * from somefunc6() ;
 id |   name    
----+-----------
  1 | wangzhen
  1 | xiaozhang
  0 | admin
  0 | admin
  2 | xiaoniu
(5 rows)

-- 代码23
-- 通过return next 返回自定义类型
create type test_rs as (id int,mc varchar);
create or replace function somefunc7()
returns setof test_rs as 
$$
declare
   r test_rs%rowtype;
begin
   for r in select n_id,c_mc from test1
   loop
      return next r;
   end loop;
   return;
end
$$ language plpgsql;

-- 代码24
-- 通过return query 返回自定义类型
create or replace function somefunc7()
returns setof test_rs as 
$$
declare
   r test_rs%rowtype;
begin
   return query select n_id,c_mc from test1;
   return;
end
$$ language plpgsql;

-- 代码25
-- 通过return next返回表类型
create or replace function somefunc7()
returns setof test1 as 
$$
declare
   r test1%rowtype;
begin
   for r in select n_id,c_mc from test1
   loop
      return next r;
   end loop;
   return;
end
$$ language plpgsql;

-- 代码26
-- 通过拼接sql  return next 返回自定义类型
create or replace function somefunc7()
returns setof test_rs as 
$$
declare
   r test_rs%rowtype;
begin
   for r in execute 'select n_id,c_mc from test1'
   loop
      return next r;
   end loop;
   return;
end
$$ language plpgsql;

-- 代码26
-- 通过拼接sql  return query 返回自定义类型
create or replace function somefunc7()
returns setof test_rs as 
$$
declare
   r test_rs%rowtype;
begin
   return query execute 'select n_id,c_mc from test1';
   return;
end
$$ language plpgsql;

• 返回结果集时PostgreSQL 9.5.4，需要使用自定义类型或表类型制定返回类型，不能用record匿名类型。

循环判断

• LOOP循环

create or replace function testloop1() 
returns void as
$$
declare
    count int :=0;
begin
    loop
       exit when count >=100;
       count := count + 1;
       raise notice 'count is %',count;
    end loop;
end
$$ language plpgsql ;

• WHILE循环

create or replace function testloop2() 
returns void as
$$
declare
    count int :=0;
begin
    while count <100 loop
       count := count + 1;
       raise notice 'count is %',count;
    end loop;
end
$$ language plpgsql ;

• FOR循环

create or replace function testloop3() 
returns void as
$$
begin
  for i in 1..100 loop
     raise notice 'count is %',i;
  end loop;
end
$$ language plpgsql;

create or replace function testloop4() 
returns void as
$$
begin
  for i in reverse 100..1 by 2 loop 
     raise notice 'count is %',i;
  end loop;
end
$$ language plpgsql;

• FOREACH循环

create or replace function testloop5()
returns void as
$$
declare
  v_arr int[]:= array[1,2,3,4,5];
  i int;
begin
  foreach i in array v_arr loop
      raise notice 'count is %',i;
  end loop;
end
$$ language plpgsql;