注意: 达梦数据库谓词无法推进VIEW，table最大查询优化个数限制（8 or 9）

原创 weizhao.zhang （anbob） 2023-08-17

392

达梦数据库(v8)在设计和实现上参考了Oracle数据库，并提供了一些兼容Oracle的功能和语法。这使得在某些情况下，可以将Oracle数据库应用迁移到达梦数据库上，而无需进行大量的修改和调整。但并不是所有的Oracle功能和特性都完全支持。在进行迁移或使用Oracle兼容性功能时，建议先进行充分的测试和验证，确保功能的正确性和性能的满足。最近协助一客户优化已上线2年的DM库，当view修改定义增加超过一定数量的union all后性能突然变差的案例。

描述一下背景，某客户的业务数据量很少，前台页面需要查询的数据来自多个表，对加载时间有较高的要求。数据源是一个view，该view中包含了几个单表数据的union all操作。随着业务的增加，union all的结果集也在不断增加。然而，当增加到第9个union all时，查询的响应时间突然增加近10倍。但是，当将最后一个view单独作为子查询时，查询速度却非常快（小于20毫秒）。是否达梦数据库对一个view中的union all操作有限制？

构建测试环境

SQL> select * from v$version;

行号     BANNER
---------- ---------------------------------
1          DM Database Server 64 V8
2          DB Version: 0x7000c
3          03134283890-20220720-165295-10045


create table test1(id int,name varchar2(200),addr VARCHAR2(300),sec char(1),dept number(3);

insert into test1 select rownum,'anbob.com'||rownum,lpad('*',30,'*'),'1',mod(rownum,5) from dual connect by rownum<=1e4;
create table test2 as select * from test1;
...
create table test7 as select * from test1;
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note:
上面构建几张测试表，可以在id列创建索引或定义主键，但不影响这们测试结果。

创建2张view

CREATE OR REPLACE VIEW V_TEST8 AS 
SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST1 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST2 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST3 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST4 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST5 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST6 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST8 WHERE SEX = '1'
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1' 
;

CREATE OR REPLACE VIEW V_TEST9 AS 
SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST1 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST2 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST3 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST4 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST5 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST6 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST8 WHERE SEX = '1'
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1' 
;
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Note:
V_TEST8 视图8个union all，一共9张表， V_TEST9 视图9个union all，一共10张表.

达梦数据库执行计划

NSET2 结果收集执行计划最顶层操作符
PRJT2 投影
SLCT2 选择表示过滤
FAGR2 快速聚集 select count(*) from 表; 会自动走这个执行计划
CSCN2 全表扫描 cluster index scan 的缩写，达梦默认创建的表是索引组织表
AAGR2 聚集用于无group by的count,sum,max,min,avg运算
HAGR2 分组聚集用于全表扫描GROUP BY聚集
BLKUP2 回表
SSEK2 二级索引扫描
SSCN 索引全扫描不回表
CSEK2 聚集索引扫描不回表

对比2个view的谓词推进

SQL> EXPLAIN SELECT * FROM V_TEST8 WHERE ID=1;

1   #NSET2: [22, 56, 226]
2     #PRJT2: [22, 56, 226]; exp_num(6), is_atom(FALSE)
3       #PRJT2: [22, 56, 226]; exp_num(6), is_atom(FALSE)
4         #UNION ALL: [22, 56, 226]
5           #PRJT2: [19, 50, 226]; exp_num(6), is_atom(FALSE)
6             #UNION ALL: [19, 50, 226]
7               #PRJT2: [17, 43, 226]; exp_num(6), is_atom(FALSE)
8                 #UNION ALL: [17, 43, 226]
9                   #PRJT2: [14, 37, 226]; exp_num(6), is_atom(FALSE)
10                    #UNION ALL: [14, 37, 226]
11                      #PRJT2: [11, 31, 226]; exp_num(6), is_atom(FALSE)
12                        #UNION ALL: [11, 31, 226]
13                          #PRJT2: [9, 25, 226]; exp_num(6), is_atom(FALSE)
14                            #UNION ALL: [9, 25, 226]
15                              #PRJT2: [6, 18, 226]; exp_num(6), is_atom(FALSE)
16                                #UNION ALL: [6, 18, 226]
17                                  #PRJT2: [4, 12, 226]; exp_num(6), is_atom(FALSE)
18                                    #UNION ALL: [4, 12, 226]
19                                      #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
20                                        #SLCT2: [1, 6, 226]; (TEST1.SEX = '1' AND TEST1.ID = 1)
21                                          #CSCN2: [1, 10000, 226]; INDEX33555471(TEST1)
22                                      #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
23                                        #SLCT2: [1, 6, 226]; (TEST2.SEX = '1' AND TEST2.ID = 1)
24                                          #CSCN2: [1, 10000, 226]; INDEX33555472(TEST2)
25                                  #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
26                                    #SLCT2: [1, 6, 226]; (TEST3.SEX = '1' AND TEST3.ID = 1)
27                                      #CSCN2: [1, 10000, 226]; INDEX33555473(TEST3)
28                              #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
29                                #SLCT2: [1, 6, 226]; (TEST4.SEX = '1' AND TEST4.ID = 1)
30                                  #CSCN2: [1, 10000, 226]; INDEX33555474(TEST4)
31                          #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
32                            #SLCT2: [1, 6, 226]; (TEST5.SEX = '1' AND TEST5.ID = 1)
33                              #CSCN2: [1, 10000, 226]; INDEX33555475(TEST5)
34                      #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
35                        #SLCT2: [1, 6, 226]; (TEST6.SEX = '1' AND TEST6.ID = 1)
36                          #CSCN2: [1, 10000, 226]; INDEX33555476(TEST6)
37                  #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
38                    #SLCT2: [1, 6, 226]; (TEST7.SEX = '1' AND TEST7.ID = 1)
39                      #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)
40              #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
41                #SLCT2: [1, 6, 226]; (TEST8.SEX = '1' AND TEST8.ID = 1)
42                  #CSCN2: [1, 10000, 226]; INDEX33555478(TEST8)
43          #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
44            #SLCT2: [1, 6, 226]; (TEST7.SEX = '1' AND TEST7.ID = 1)
45              #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)
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Note:
可见view 的查询谓词id=1 推进到了view内部，每个表过滤后聚合，如果表上ID列有索引还能更快。

SQL> EXPLAIN SELECT * FROM V_TEST9 WHERE ID=1;

1   #NSET2: [26, 62, 226]
2     #PRJT2: [26, 62, 226]; exp_num(6), is_atom(FALSE)
3       #SLCT2: [26, 62, 226]; V_TEST9.ID = 1
4         #PRJT2: [26, 2500, 226]; exp_num(6), is_atom(FALSE)
5           #UNION ALL: [26, 2500, 226]
6             #PRJT2: [23, 2250, 226]; exp_num(6), is_atom(FALSE)
7               #UNION ALL: [23, 2250, 226]
8                 #PRJT2: [20, 2000, 226]; exp_num(6), is_atom(FALSE)
9                   #UNION ALL: [20, 2000, 226]
10                    #PRJT2: [18, 1750, 226]; exp_num(6), is_atom(FALSE)
11                      #UNION ALL: [18, 1750, 226]
12                        #PRJT2: [15, 1500, 226]; exp_num(6), is_atom(FALSE)
13                          #UNION ALL: [15, 1500, 226]
14                            #PRJT2: [12, 1250, 226]; exp_num(6), is_atom(FALSE)
15                              #UNION ALL: [12, 1250, 226]
16                                #PRJT2: [9, 1000, 226]; exp_num(6), is_atom(FALSE)
17                                  #UNION ALL: [9, 1000, 226]
18                                    #PRJT2: [6, 750, 226]; exp_num(6), is_atom(FALSE)
19                                      #UNION ALL: [6, 750, 226]
20                                        #PRJT2: [4, 500, 226]; exp_num(6), is_atom(FALSE)
21                                          #UNION ALL: [4, 500, 226]
22                                            #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
23                                              #SLCT2: [1, 250, 226]; TEST1.SEX = '1'
24                                                #CSCN2: [1, 10000, 226]; INDEX33555471(TEST1)
25                                            #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
26                                              #SLCT2: [1, 250, 226]; TEST2.SEX = '1'
27                                                #CSCN2: [1, 10000, 226]; INDEX33555472(TEST2)
28                                        #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
29                                          #SLCT2: [1, 250, 226]; TEST3.SEX = '1'
30                                            #CSCN2: [1, 10000, 226]; INDEX33555473(TEST3)
31                                    #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
32                                      #SLCT2: [1, 250, 226]; TEST4.SEX = '1'
33                                        #CSCN2: [1, 10000, 226]; INDEX33555474(TEST4)
34                                #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
35                                  #SLCT2: [1, 250, 226]; TEST5.SEX = '1'
36                                    #CSCN2: [1, 10000, 226]; INDEX33555475(TEST5)
37                            #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
38                              #SLCT2: [1, 250, 226]; TEST6.SEX = '1'
39                                #CSCN2: [1, 10000, 226]; INDEX33555476(TEST6)
40                        #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
41                          #SLCT2: [1, 250, 226]; TEST7.SEX = '1'
42                            #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)
43                    #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
44                      #SLCT2: [1, 250, 226]; TEST8.SEX = '1'
45                        #CSCN2: [1, 10000, 226]; INDEX33555478(TEST8)
46                #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
47                  #SLCT2: [1, 250, 226]; TEST7.SEX = '1'
48                    #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)
49            #PRJT2: [1, 250, 226]; exp_num(6), is_atom(FALSE)
50              #SLCT2: [1, 250, 226]; TEST7.SEX = '1'
51                #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)

已用时间: 2.464(毫秒). 执行号:0.
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NOTE:
当增加到第9个union all(或union、minus)后, 执行计划改变，谓词并没有推进，而是当view内所有结果聚合后过滤。业务SQL同样的现象，无论第9个union all是什么查询(即使是前8个中的查询)，排查因第9个union all语法限制。

业务SQL的执行计划对比

select * from WK_V_XXXXX_2023-08-14 where id='11';

77          #PRJT2: [1, 1, 432]; exp_num(18), is_atom(FALSE) 
78            #SLCT2: [1, 1, 432]; (TABLE_XXXXXX.IS_DELETE = '0' AND TABLE_XXXXXX.STATUS = '1')
79              #BLKUP2: [1, 1, 432]; INDEX33557689(TABLE_XXXXXX)
80                #SSEK2: [1, 1, 432]; scan_type(ASC), INDEX33557689(TABLE_XXXXXX), scan_range['11','11']   ---id 列 unique index 

-- 超过9个(含)union all后的view，执行计划变为下面:

2     #PRJT2: [271, 1162, 864]; exp_num(18), is_atom(FALSE) 
3       #SLCT2: [271, 1162, 864]; WK_V_XXXXX_2023-08-14.id = '11'
...
76            #PRJT2: [1, 1, 432]; exp_num(18), is_atom(FALSE) 
77              #BLKUP2: [1, 1, 432]; TABLE_XXXXXX_IS_DELETE_STATUS_0717(TABLE_XXXXXX)
78                #SSEK2: [1, 1, 432]; scan_type(ASC), TABLE_XXXXXX_IS_DELETE_STATUS_0717(TABLE_XXXXXX), scan_range[('0','1'),('0','1')]


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Note:
谓词没有推进，还使用了选择率不好的二级索引delete state类似性别状态列的索引再回表，所以响应时间明显增加。尝试增加merge hint无法改变执行计划。

查看数据库参数

SQL> select * from v$dm_ini where PARA_VALUE in ('8','9') or MAX_VALUE in ('8','9');

行号     PARA_NAME            PARA_VALUE MIN_VALUE MAX_VALUE  DEFAULT_VALUE MPP_CHK SESS_VALUE FILE_VALUE DESCRIPTION                                                                 PARA_TYPE
---------- -------------------- ---------- --------- ---------- ------------- ------- ---------- ---------- --------------------------------------------------------------------------- ---------
1          KEEP                 8          8         1048576    8             N       8          8          Initial System KEEP Buffer Size In Megabytes                                IN FILE
2          MTAB_MEM_SIZE        8          1         1048576    8             N       8          8          mtab memory size in KB                                                      IN FILE
3          CASE_WHEN_CVT_IFUN   9          0         63         9             N       9          9          Flag of converting subquery in case-when expression to IF operator          SESSION
4          SPEED_SEMI_JOIN_PLAN 9          0         31         9             N       9          9          Flag of speeding up the generating process of semi join plan                SESSION
5          FORCE_FLUSH_PAGES    8          0         1000       8             N       8          8          Schedule Thread Force Flush Pages                                           SYS
6          IO_THR_GROUPS        8          1         512        8             N       8          8          The Number Of Io Thread Groups(Non-Windows Only)                            IN FILE
7          HLDR_BUF_SIZE        8          4         1024       8             N       8          8          HUGE table fast loader buffer size in Megabytes                             SYS
8          DBLINK_LOB_LEN       8          4         1024       8             N       8          8          BLOB/TEXT buffer size(KB) for dblink                                        SYS
9          PWD_MIN_LEN          9          9         48         9             N       9          9          Password min length in byte, it's valid only if PWD_POLICY&2 not equal to 0 SYS
10         UDP_BTU_COUNT        8          4         32         8             N       8          8          Count of udp batch transfer units                                           IN FILE
11         PAGE_TAIL_SIZE       8          0         4294967294 8             N       8          8          page_tail_size                                                              READ ONLY
12         DSC_FREQ_CONFLICT    8          1         1000       8             N       8          8          High frequency conflict counts                                              SYS
13         MAX_OPT_N_TABLES     6          3         8          6             N       6          6          Maximum Number Of Tables For Query Optimization                             SESSION

13 rows got


SQL> select name ,type,value,sys_value,file_value,description from v$parameter where upper(name) like upper('%max%\_N\_%') escape '\';

行号     NAME                TYPE    VALUE SYS_VALUE FILE_VALUE DESCRIPTION
---------- ------------------- ------- ----- --------- ---------- ------------------------------------------------------------
1          MAX_OPT_N_TABLES    SESSION 6     6         6          Maximum Number Of Tables For Query Optimization
2          MAX_N_GRP_PUSH_DOWN SESSION 5     5         5          Maximum Number Of RELs For GRP push down Optimization
3          MAX_OPT_N_OR_BEXPS  SESSION 7     7         7          maximum number of OR bool expressions for query optimization

SQL> select para_name,para_value,MAX_VALUE,DEFAULT_VALUE,DESCRIPTION,PARA_TYPE from v$dm_ini where para_name like '%&1%';

行号     PARA_NAME           PARA_VALUE MAX_VALUE DEFAULT_VALUE DESCRIPTION                                                       PARA_TYPE
---------- ------------------- ---------- --------- ------------- ----------------------------------------------------------------- ---------
1          VIEW_PULLUP_MAX_TAB 7          16        7             Maximum number of tables that can be handled when pulling up view SESSION


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Note:
在达梦数据库中确实有一些表个数的查询优化限制，但修改参数未能解决，怀疑是数据库软件hard code编码限制。

临时解决方法：
1，改写SQL减少同一层子查询的个数，如合并前面查询
2，其中部分union all 创建为中间view, 在主view 拼接
3，在view定义中再增加一层部分view的子查询,如下：

CREATE OR REPLACE VIEW V_TEST9_2 AS 
SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST1 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST2 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST3 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST4 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST5 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST6 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1' 
UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST8 WHERE SEX = '1'
UNION  ALL  select * from (
                            SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1' 
                            UNION  ALL  SELECT "ID","NAME","ADDR","SEX","REMARK","DEPT" FROM TEST7 WHERE SEX = '1'
 							)
;


SQL> EXPLAIN SELECT * FROM V_TEST9_2 WHERE ID=1;

1   #NSET2: [24, 62, 226]
2     #PRJT2: [24, 62, 226]; exp_num(6), is_atom(FALSE)
3       #PRJT2: [24, 62, 226]; exp_num(6), is_atom(FALSE)
4         #UNION ALL: [24, 62, 226]
5           #PRJT2: [19, 50, 226]; exp_num(6), is_atom(FALSE)
6             #UNION ALL: [19, 50, 226]
7               #PRJT2: [17, 43, 226]; exp_num(6), is_atom(FALSE)
8                 #UNION ALL: [17, 43, 226]
9                   #PRJT2: [14, 37, 226]; exp_num(6), is_atom(FALSE)
10                    #UNION ALL: [14, 37, 226]
11                      #PRJT2: [11, 31, 226]; exp_num(6), is_atom(FALSE)
12                        #UNION ALL: [11, 31, 226]
13                          #PRJT2: [9, 25, 226]; exp_num(6), is_atom(FALSE)
14                            #UNION ALL: [9, 25, 226]
15                              #PRJT2: [6, 18, 226]; exp_num(6), is_atom(FALSE)
16                                #UNION ALL: [6, 18, 226]
17                                  #PRJT2: [4, 12, 226]; exp_num(6), is_atom(FALSE)
18                                    #UNION ALL: [4, 12, 226]
19                                      #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
20                                        #SLCT2: [1, 6, 226]; (TEST1.SEX = '1' AND TEST1.ID = 1)
21                                          #CSCN2: [1, 10000, 226]; INDEX33555471(TEST1)
22                                      #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
23                                        #SLCT2: [1, 6, 226]; (TEST2.SEX = '1' AND TEST2.ID = 1)
24                                          #CSCN2: [1, 10000, 226]; INDEX33555472(TEST2)
25                                  #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
26                                    #SLCT2: [1, 6, 226]; (TEST3.SEX = '1' AND TEST3.ID = 1)
27                                      #CSCN2: [1, 10000, 226]; INDEX33555473(TEST3)
28                              #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
29                                #SLCT2: [1, 6, 226]; (TEST4.SEX = '1' AND TEST4.ID = 1)
30                                  #CSCN2: [1, 10000, 226]; INDEX33555474(TEST4)
31                          #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
32                            #SLCT2: [1, 6, 226]; (TEST5.SEX = '1' AND TEST5.ID = 1)
33                              #CSCN2: [1, 10000, 226]; INDEX33555475(TEST5)
34                      #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
35                        #SLCT2: [1, 6, 226]; (TEST6.SEX = '1' AND TEST6.ID = 1)
36                          #CSCN2: [1, 10000, 226]; INDEX33555476(TEST6)
37                  #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
38                    #SLCT2: [1, 6, 226]; (TEST7.SEX = '1' AND TEST7.ID = 1)
39                      #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)
40              #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
41                #SLCT2: [1, 6, 226]; (TEST8.SEX = '1' AND TEST8.ID = 1)
42                  #CSCN2: [1, 10000, 226]; INDEX33555478(TEST8)
43          #PRJT2: [4, 12, 226]; exp_num(6), is_atom(FALSE)
44            #PRJT2: [4, 12, 226]; exp_num(6), is_atom(FALSE)
45              #UNION ALL: [4, 12, 226]
46                #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
47                  #SLCT2: [1, 6, 226]; (TEST7.SEX = '1' AND TEST7.ID = 1)
48                    #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)
49                #PRJT2: [1, 6, 226]; exp_num(6), is_atom(FALSE)
50                  #SLCT2: [1, 6, 226]; (TEST7.SEX = '1' AND TEST7.ID = 1)
51                    #CSCN2: [1, 10000, 226]; INDEX33555477(TEST7)

已用时间: 2.888(毫秒). 执行号:0.

注： 本人仅对达梦研究处于初期，如果有表达错误，欢迎指正。
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— over —

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注意: 达梦数据库谓词无法推进VIEW，table最大查询优化个数限制（8 or 9）

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