PostgreSQL 游标的种类

1.说明：

1）cursor和refcursor的区别：
静态游标，不能修改里面的语句
动态游标，可以多次open和close，指定不同的SQL
隐式游标，DML和for操作，都在内部转换为了一个隐式游标在执行

2）fetch的区别：
使用fetch cur 和 fetch next from cur 一样，因为NEXT 是 FETCH 的默认选项.

2.创建测试表：

create table test(id int, info text, crt_time timestamp);
insert into test select generate_series(1,10), 'test', now();

　　

3.测试：

DO
$$
DECLARE
id integer;
one_row record;
ret_cur CURSOR FOR SELECT * FROM test; --静态游标，不能修改里面的语句
ret_cur2 refcursor;--动态游标，可以多次open和close，指定不同的SQL
BEGIN
id:=1;
raise notice 'test id: %', id;

--动态游标
OPEN ret_cur2 FOR SELECT * FROM test;
FETCH ret_cur2 INTO one_row;
while ret_cur2%FOUND loop
raise notice 'row info, id is: %, info is: %, crt_time is: %', one_row.id, one_row.info, one_row.crt_time;
FETCH ret_cur2 INTO one_row;
END loop;
CLOSE ret_cur2;

raise notice 'user fetch next: ';

--静态游标：
OPEN ret_cur;
FETCH NEXT FROM ret_cur INTO one_row;
while ret_cur%FOUND loop
raise notice 'row info, id is: %, info is: %, crt_time is: %', one_row.id, one_row.info, one_row.crt_time;
FETCH NEXT FROM ret_cur INTO one_row;
END loop;
CLOSE ret_cur;


--隐式游标，实际上select * from test是存在一个内部的游标中的：
raise notice '隐式游标：';
FOR one_row IN (SELECT * FROM test) loop
raise notice 'row info, id is: %, info is: %, crt_time is: %', one_row.id, one_row.info, one_row.crt_time;
END loop;

--最后执行：
EXCEPTION WHEN NO_DATA_FOUND THEN 
raise notice 'no data FOUND';

END 
$$

　　

4.执行结果：

00000: test id: 1
00000: row info, id is: 1, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 2, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 3, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 4, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 5, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 6, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 7, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 8, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 9, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 10, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: user fetch next: 
00000: row info, id is: 1, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 2, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 3, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 4, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 5, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 6, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 7, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 8, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 9, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 10, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: 隐式游标：
00000: row info, id is: 1, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 2, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 3, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 4, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 5, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 6, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 7, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 8, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 9, info is: test, crt_time is: 2020-09-09 15:01:35.837492
00000: row info, id is: 10, info is: test, crt_time is: 2020-09-09 15:01:35.837492

　　

5.游标属性：

%FOUND： bool - TRUE if >1 row returned 
%NOTFOUND：bool - TRUE if 0 rows returned 
%ISOPEN： bool - TRUE if cursor still open 
%ROWCOUNT：int - number of rows affected by last SQL statement

注：NO_DATA_FOUND和%NOTFOUND的用法是有区别的，小结如下： 
1）SELECT . . . INTO 语句触发 NO_DATA_FOUND； 
2）当一个显式光标的 where 子句未找到时触发 %NOTFOUND； 
3）当UPDATE或DELETE 语句的where 子句未找到时触发 SQL%NOTFOUND； 
4）在光标的提取(Fetch)循环中要用 %NOTFOUND 或%FOUND 来确定循环的退出条件，不要用NO_DATA_FOUND