（1）如果函数返回一个标量类型，表达式结果将自动转行成函数的返回类型。但要返回一个复合（行）值，必须写一个所需列集合的表达式。

标量示例

create or replace function fn_scalar() returns numeric as 
$$
declare 
begin 
	return (3+4*2)-(2*2-1);
end
$$
language plpgsql

select * from fn_scalar();

select * from fn_scalar() as cnt

复合示例

create or replace function fn_scalars() returns record as 
$$
declare 
begin 
	return (1,2,'hello world'::text);
end
$$
language plpgsql

select * from fn_scalars() as (no1 int,no2 int,msg text);

（2）如果声明带输出参数的函数，只需要写不带表达式的RETURN，输出参数变量的当前值被返回

有返回值

create or replace function fn_out_return(out rcd text) returns text as 
$$
declare 
begin 
	select name into rcd from product where id = 1 ;
end

$$
language plpgsql

select * from fn_out_return ()

函数返回void

如果声明函数返回void，RETURN可以用来提前结果函数，但函数最后不要写RETURN

create or replace function fn_void_return() returns void as 
$$
declare 
begin 
	raise notice '执行第一行....';
	raise notice '执行第二行....';
return;
	raise notice '执行第三行....';
end

$$ 
language plpgsql

select * from fn_void_return() 

执行第一行…
执行第二行…

RETURN NEXT ,RETURN QUERY

当函数被声明为返回returns setof sometype,规则和直接return sometype有所不同。这种情况下，返回的个体项被RETURN NEXT或者RETURN QUERY 命令序列指定，并接着会用一个不带参数的RETURN命令来指示这个函数已经完成执行。

（1）RETURN NEXT可以返回标量和复合类型，对于复合类型，将返回一个完整的结果“表”（结果集）。

create or replace function fn_return_nexts() returns setof product as 
$$
declare 
r product%rowtype;
begin 
	for r in select * from product
	loop
		
		raise notice 'name is :%',r.name;
	    return next r;
	end loop;
return;
end

$$
language plpgsql

select * from fn_return_nexts()

name is :diam
name is :vestibulum aliquet
name is :lacinia erat
name is :scelerisque quam turpis
name is :justo lacinia
name is :ultrices mattis odio
name is :hendrerit
name is :in hac habitasse
name is :orci eget orci
name is :pellentesque
name is :sit amet nunc
name is :sed vestibulum
name is :turpis eget
name is :cursus vestibulum
name is :orci nullam
name is :est quam pharetra
name is :posuere
name is :ligula
name is :convallis
name is :nulla elit ac

（2）RETURN QUERY 将执行一个查询的结果追加到一个函数结果中。

create or replace function fn_return_query() returns setof product as 
$$
declare 
r record;
begin 
	return query(select * from product);

end

$$
language plpgsql

select * from fn_return_query()

返回结果同上所示

RETURN EXECUTE

create or replace function fn_query_execute(v_name varchar) returns setof product as 
$$
declare 
_sql text;
begin 
	_sql := 'select * from product where name like '''|| v_name || '%'';';
	raise notice 'sql====%',_sql;
return query execute _sql;
end

$$ 
language plpgsql

select * from fn_query_execute('s')

sql====select * from product where name like ‘s%’;

IF THEN END IF

create or replace function fn_if_else(uid int) returns text as
$$
declare
v_value text;
begin
if uid = 1 then
v_value='参数值为1';
else
v_value='参数值不为1';
end if;
return v_value;
end 
$$
language plpgsql

FOREACH,LOOP

https://blog.csdn.net/qq_39727113/article/details/115756087

SLICE

create or replace function fn_foreach(int[]) returns void as 
$$
declare 
x int;
begin 
	foreach x slice 0 in array $1
	loop 
	  raise notice '输出value=%',x;	
	end loop;
	
end

$$
language plpgsql

select * from fn_foreach(array[[1,2,3],[4,5,6]]);
输出value=1
输出value=2
输出value=3
输出value=4
输出value=5
输出value=6

select * from fn_foreach(array[1,2,3])
输出value=1
输出value=2
输出value=3

create or replace function fn_foreach(int[]) returns void as 
$$
declare 
x int[];
begin 
	foreach x slice 2 in array $1
	loop 
	  raise notice '输出value=%',x;	
	end loop;
	
end

$$
language plpgsql

select * from fn_foreach(array[[1,2,3],[4,5,6]]);
输出value={{1,2,3},{4,5,6}}