比较的版本和配置
Oracle 19c
docker pull registry.cn-hangzhou.aliyuncs.com/zhuyijun/oracle:19c
SQL> SELECT BANNER_FULL FROM V$VERSION;
BANNER_FULL
--------------------------------------------------------------------------------
Oracle Database 19c Standard Edition 2 Release 19.0.0.0.0 - Production
Version 19.3.0.0.0
SQL> show sga;
Total System Global Area 3137338784 bytes
Fixed Size 9141664 bytes
Variable Size 654311424 bytes
Database Buffers 2466250752 bytes
Redo Buffers 7634944 bytes达梦
wget http://download.dameng.com/eco/dm8/dm8_20250206_x86_rh6_rq_single.tar
docker load -i ./dm8_20250206_x86_rh6_rq_single.tar
SQL> SELECT * FROM v$version;
LINEID BANNER
---------- ---------------------------------
1 DM Database Server 64 V8
2 DB Version: 0x7000d
3 03134284336-20250117-257733-20132
4 Msg Version: 32
5 Gsu level(5) cnt: 01.connect by语句
Oracle：
SQL> col a for 999999999999999
SQL> select sum(level) a from dual connect by level<=1e6;
A
----------------
500000500000
Elapsed: 00:00:00.22
SQL> select sum(i)a,substr(i,1,1) from(select level i from dual connect by level<=1e6)group by substr(i,1,1);
A SUBS
---------------- ----
85858530303 8
25252469697 2
55555500000 5
65656510101 6
75757520202 7
15152459596 1
35353479798 3
45454489899 4
95959540404 9
9 rows selected.
Elapsed: 00:00:00.24
SQL> select sum(level) a from dual connect by level<=1e7;
select sum(level) a from dual connect by level<=1e7
*
ERROR at line 1:
ORA-30009: Not enough memory for CONNECT BY operation
Elapsed: 00:00:00.29
SQL> select sum(level) a from dual connect by level<=3e6;
select sum(level) a from dual connect by level<=3e6
*
ERROR at line 1:
ORA-30009: Not enough memory for CONNECT BY operation
Elapsed: 00:00:00.22
SQL> select sum(level) a from dual connect by level<=2e6;
A
----------------
2000001000000
Elapsed: 00:00:00.25
SQL> select sum(i)a,substr(i,1,1) from(select level i from dual connect by level<=2e6)group by substr(i,1,1);
A SUBS
---------------- ----
85858530303 8
25254469697 2
55555500000 5
65656510101 6
75757520202 7
1515150959596 1
35353479798 3
45454489899 4
95959540404 9
9 rows selected.
Elapsed: 00:00:00.48可能是内存设置问题，千万行、三百万行connect by level均报内存不足。
百万行简单加总220毫秒，按数字第一个字符分组汇总240毫秒, 二百万行简单加总240毫秒，按数字第一个字符分组汇总480毫秒。
达梦：
SQL> select sum(level) from dual connect by level<=1e6;
LINEID SUM(LEVEL)
---------- --------------------
1 500000500000
used time: 47.203(ms). Execute id is 1817.
SQL> select sum(i)a,substr(i,1,1) from(select level i from dual connect by level<=1e6)group by substr(i,1,1);
LINEID A SUBSTR(I,1,1)
---------- -------------------- -------------
1 15152459596 1
2 25252469697 2
3 35353479798 3
4 45454489899 4
5 55555500000 5
6 65656510101 6
7 75757520202 7
8 85858530303 8
9 95959540404 9
9 rows got
used time: 114.917(ms). Execute id is 805.
SQL> select sum(level) a from dual connect by level<=2e6;
LINEID A
---------- --------------------
1 2000001000000
used time: 121.851(ms). Execute id is 807.
SQL> select sum(i)a,substr(i,1,1) from(select level i from dual connect by level<=2e6)group by substr(i,1,1);
LINEID A SUBSTR(I,1,1)
---------- -------------------- -------------
1 1515150959596 1
2 25254469697 2
3 35353479798 3
4 45454489899 4
5 55555500000 5
6 65656510101 6
7 75757520202 7
8 85858530303 8
9 95959540404 9
9 rows got
used time: 205.320(ms). Execute id is 806.
SQL> select sum(level) from dual connect by level<=1e7;
LINEID SUM(LEVEL)
---------- --------------------
1 50000005000000
used time: 432.414(ms). Execute id is 1818.
SQL> select sum(i),substr(i,1,1) from(select level i from dual connect by level<=1e7)group by substr(i,1,1);
LINEID SUM(I) SUBSTR(I,1,1)
---------- -------------------- -------------
1 1515160959596 1
2 2525251969697 2
3 3535352979798 3
4 4545453989899 4
5 5555555000000 5
6 6565656010101 6
7 7575757020202 7
8 8585858030303 8
9 9595959040404 9
used time: 845.997(ms). Execute id is 1819.百万行简单加总47毫秒，按数字第一个字符分组汇总115毫秒, 二百万行简单加总122毫秒，按数字第一个字符分组汇总205毫秒。千万行简单加总432毫秒，按数字第一个字符分组汇总846毫秒。
按比例推算Oracle比达梦慢一半。
2.with function功能
Oracle
SQL> WITH FUNCTION f1(C INT) RETURN INT AS BEGIN RETURN C* 10; END;
2 SELECT f1(5236) FROM DUAL;
3 /
F1(5236)
----------
52360
计算阶乘
SQL> WITH FUNCTION fac(C INT) RETURN INT AS BEGIN RETURN case when C=1 then 1 else C* fac(C-1) end; END;
SELECT fac(22)f FROM DUAL;
/
F
--------------------------
1124000727777607680000
Elapsed: 00:00:00.01
计算斐波那契数
SQL> WITH FUNCTION fib(C INT) RETURN INT AS BEGIN RETURN case when C=1 or C=2 then 1 else fib(C-1)+ fib(C-2) end; END;
SELECT fib(35)f FROM DUAL;
/
F
--------------------------
9227465
Elapsed: 00:00:01.76基本的函数，递归调用的函数都可以执行成功
达梦
SQL> WITH FUNCTION f1(C INT) RETURN INT AS BEGIN RETURN C* 10; END;
2 SELECT f1(5236) FROM DUAL;
3 /
LINEID F1(5236)
---------- -----------
1 52360
used time: 2.382(ms). Execute id is 66303.
WITH FUNCTION fac(C INT) RETURN INT AS BEGIN RETURN case when C=1 then 1 else C* fac(C-1) end; END;
SELECT fac(22)f FROM DUAL;
[-7057]:Too many nested level
-7057: FAC line 1
....
used time: 710.387(ms). Execute id is 0.
WITH FUNCTION fib(C INT) RETURN INT AS BEGIN RETURN case when C=1 or C=2 then 1 else fib(C-1)+ fib(C-2) end; END;
SELECT fib(35)f FROM DUAL;
[-7057]:Too many nested level
-7057: FIB line 1
....
used time: 743.573(ms). Execute id is 0.最基本的函数可以，递归调用的函数定义不报错但不能实用。搜索报错信息，参照这篇文章相关dm.ini参数配置如下
EXPR_N_LEVEL = 200 #Maximum nesting levels for expression
N_PARSE_LEVEL = 100 #Maximum nesting levels for parsing object
MAX_SQL_LEVEL = 500 #Maximum nesting levels of VM stack frame for sql修改参数还要重启服务就不测试了。