Oracle VIEW 显示在我的表中创建最后一条记录的时间
Oracle VIEW showing when last records were created in my tables
我有 tables t1 和 t2，它们都有包含创建每条记录时的时间戳的列 created_on。平常事。
现在我想创建一个视图来显示我的 tables 和最后创建的记录的时间戳 (MAX(created_on)) 在相应的 table.
结果应如下所示：
table | last_record
======+============
t1 | 10.05.2019
t2 | 12.11.2020
例如，我可以通过以下方式检索我的 table 的列表：
SELECT * FROM USER_TABLES WHERE table_name LIKE 'T%'
我想获取每个 table 的最后一条记录的时间戳。
如何创建这个视图？
这可能取决于表的描述；我认为它们之间存在某种关联。
无论如何：这就是我对这个问题的理解。阅读代码中的注释。
SQL> with
2 -- sample data
3 t1 (id, name, created_on) as
4 (select 1, 'Little', date '2021-12-14' from dual union all --> max for Little
5 select 2, 'Foot' , date '2021-12-13' from dual union all --> max for Foot
6 select 2, 'Foot' , date '2021-12-10' from dual
7 ),
8 t2 (id, name, created_on) as
9 (select 2, 'Foot' , date '2021-12-09' from dual union all
10 select 3, 'SBrbot', date '2021-12-14' from dual --> max for SBrbot
11 )
12 -- query you'd use for a view
13 select id, name, max(created_on) max_created_on
14 from
15 -- union them, so that it is easier to find max date
16 (select id, name, created_on from t1
17 union all
18 select id, name, created_on from t2
19 )
20 group by id, name;
ID NAME MAX_CREATE
---------- ------ ----------
1 Little 14.12.2021
2 Foot 13.12.2021
3 SBrbot 14.12.2021
SQL>
在您解决问题之后，这就更容易了；查看查询从第 12 行开始：
SQL> with
2 -- sample data
3 t1 (id, name, created_on) as
4 (select 1, 'Little', date '2021-12-14' from dual union all
5 select 2, 'Foot' , date '2021-12-13' from dual union all
6 select 2, 'Foot' , date '2021-12-10' from dual
7 ),
8 t2 (id, name, created_on) as
9 (select 2, 'Foot' , date '2021-12-09' from dual union all
10 select 3, 'SBrbot', date '2021-12-14' from dual
11 )
12 select 't1' source_table, max(created_on) max_created_on from t1
13 union
14 select 't2' source_table, max(created_on) max_created_on from t2;
SO MAX_CREATE
-- ----------
t1 14.12.2021
t2 14.12.2021
SQL>
如果它必须是 动态的，一种选择是创建一个 returns 引用游标的函数：
SQL> create or replace function f_max
2 return sys_refcursor
3 is
4 l_str varchar2(4000);
5 rc sys_refcursor;
6 begin
7 for cur_r in (select distinct c.table_name
8 from user_tab_columns c
9 where c.column_name = 'CREATED_ON'
10 order by c.table_name
11 )
12 loop
13 l_str := l_str ||' union all select ' || chr(39) || cur_r.table_name || chr(39) ||
14 ' table_name, max(created_on) last_updated from ' || cur_r.table_name;
15 end loop;
16
17 l_str := ltrim(l_str, ' union all ');
18
19 open rc for l_str;
20 return rc;
21 end;
22 /
Function created.
测试：
SQL> select f_max from dual;
F_MAX
--------------------
CURSOR STATEMENT : 1
CURSOR STATEMENT : 1
TA LAST_UPDAT
-- ----------
T1 14.12.2021
T2 14.12.2021
SQL>
I have 30+ tables and wanted avoid hard coding SELECT statements for each of these tables and UNION them all. I expected some solution where I would insert tablenames in kinda array and create JOIN to show result with all last records. I know problem is here that tablename is variable!
您不能在 SQL 中执行此操作，因为 VIEW 是在编译时设置的，并且表必须是已知的；你能做的最好的事情是在 PL/SQL 中动态创建一个 SQL 语句，然后使用 EXECUTE IMMEDIATE 然后重新 运行 如果你想重新创建视图：
DECLARE
v_tables SYS.ODCIVARCHAR2LIST := SYS.ODCIVARCHAR2LIST(
'TABLE1', 'TABLE2', 'table3', 'TABLE5'
);
v_sql CLOB := 'CREATE OR REPLACE VIEW last_dates (table_name, last_date) AS ';
BEGIN
FOR i in 1 .. v_tables.COUNT LOOP
IF i > 1 THEN
v_sql := v_sql || ' UNION ALL ';
END IF;
v_sql := v_sql || 'SELECT '
|| DBMS_ASSERT.ENQUOTE_LITERAL(v_tables(i))
|| ', MAX(created_on) FROM '
|| DBMS_ASSERT.ENQUOTE_NAME(v_tables(i), FALSE);
END LOOP;
EXECUTE IMMEDIATE v_sql;
END;
/
然后对于示例表：
CREATE TABLE table1 (created_on) AS
SELECT SYSDATE - LEVEL FROM DUAL CONNECT BY LEVEL <= 3;
CREATE TABLE table2 (created_on) AS
SELECT SYSDATE - LEVEL FROM DUAL CONNECT BY LEVEL <= 3;
CREATE TABLE "table3" (created_on) AS
SELECT SYSDATE - LEVEL FROM DUAL CONNECT BY LEVEL <= 3;
CREATE TABLE table5 (created_on) AS
SELECT SYSDATE FROM DUAL;
运行在 PL/SQL 块之后，然后：
SELECT * FROM last_dates;
输出：
TABLE_NAME
LAST_DATE
TABLE1
2021-12-13 13:21:58
TABLE2
2021-12-13 13:21:59
table3
2021-12-13 13:21:59
TABLE5
2021-12-14 13:21:59
db<>fiddle here
我有 tables t1 和 t2，它们都有包含创建每条记录时的时间戳的列 created_on。平常事。
现在我想创建一个视图来显示我的 tables 和最后创建的记录的时间戳 (MAX(created_on)) 在相应的 table.
结果应如下所示：
table | last_record
======+============
t1 | 10.05.2019
t2 | 12.11.2020
例如，我可以通过以下方式检索我的 table 的列表：
SELECT * FROM USER_TABLES WHERE table_name LIKE 'T%'
我想获取每个 table 的最后一条记录的时间戳。
如何创建这个视图？
这可能取决于表的描述；我认为它们之间存在某种关联。
无论如何：这就是我对这个问题的理解。阅读代码中的注释。
SQL> with
2 -- sample data
3 t1 (id, name, created_on) as
4 (select 1, 'Little', date '2021-12-14' from dual union all --> max for Little
5 select 2, 'Foot' , date '2021-12-13' from dual union all --> max for Foot
6 select 2, 'Foot' , date '2021-12-10' from dual
7 ),
8 t2 (id, name, created_on) as
9 (select 2, 'Foot' , date '2021-12-09' from dual union all
10 select 3, 'SBrbot', date '2021-12-14' from dual --> max for SBrbot
11 )
12 -- query you'd use for a view
13 select id, name, max(created_on) max_created_on
14 from
15 -- union them, so that it is easier to find max date
16 (select id, name, created_on from t1
17 union all
18 select id, name, created_on from t2
19 )
20 group by id, name;
ID NAME MAX_CREATE
---------- ------ ----------
1 Little 14.12.2021
2 Foot 13.12.2021
3 SBrbot 14.12.2021
SQL>
在您解决问题之后，这就更容易了；查看查询从第 12 行开始：
SQL> with
2 -- sample data
3 t1 (id, name, created_on) as
4 (select 1, 'Little', date '2021-12-14' from dual union all
5 select 2, 'Foot' , date '2021-12-13' from dual union all
6 select 2, 'Foot' , date '2021-12-10' from dual
7 ),
8 t2 (id, name, created_on) as
9 (select 2, 'Foot' , date '2021-12-09' from dual union all
10 select 3, 'SBrbot', date '2021-12-14' from dual
11 )
12 select 't1' source_table, max(created_on) max_created_on from t1
13 union
14 select 't2' source_table, max(created_on) max_created_on from t2;
SO MAX_CREATE
-- ----------
t1 14.12.2021
t2 14.12.2021
SQL>
如果它必须是 动态的，一种选择是创建一个 returns 引用游标的函数：
SQL> create or replace function f_max
2 return sys_refcursor
3 is
4 l_str varchar2(4000);
5 rc sys_refcursor;
6 begin
7 for cur_r in (select distinct c.table_name
8 from user_tab_columns c
9 where c.column_name = 'CREATED_ON'
10 order by c.table_name
11 )
12 loop
13 l_str := l_str ||' union all select ' || chr(39) || cur_r.table_name || chr(39) ||
14 ' table_name, max(created_on) last_updated from ' || cur_r.table_name;
15 end loop;
16
17 l_str := ltrim(l_str, ' union all ');
18
19 open rc for l_str;
20 return rc;
21 end;
22 /
Function created.
测试：
SQL> select f_max from dual;
F_MAX
--------------------
CURSOR STATEMENT : 1
CURSOR STATEMENT : 1
TA LAST_UPDAT
-- ----------
T1 14.12.2021
T2 14.12.2021
SQL>
I have 30+ tables and wanted avoid hard coding SELECT statements for each of these tables and UNION them all. I expected some solution where I would insert tablenames in kinda array and create JOIN to show result with all last records. I know problem is here that tablename is variable!
您不能在 SQL 中执行此操作，因为 VIEW 是在编译时设置的，并且表必须是已知的；你能做的最好的事情是在 PL/SQL 中动态创建一个 SQL 语句，然后使用 EXECUTE IMMEDIATE 然后重新 运行 如果你想重新创建视图：
DECLARE
v_tables SYS.ODCIVARCHAR2LIST := SYS.ODCIVARCHAR2LIST(
'TABLE1', 'TABLE2', 'table3', 'TABLE5'
);
v_sql CLOB := 'CREATE OR REPLACE VIEW last_dates (table_name, last_date) AS ';
BEGIN
FOR i in 1 .. v_tables.COUNT LOOP
IF i > 1 THEN
v_sql := v_sql || ' UNION ALL ';
END IF;
v_sql := v_sql || 'SELECT '
|| DBMS_ASSERT.ENQUOTE_LITERAL(v_tables(i))
|| ', MAX(created_on) FROM '
|| DBMS_ASSERT.ENQUOTE_NAME(v_tables(i), FALSE);
END LOOP;
EXECUTE IMMEDIATE v_sql;
END;
/
然后对于示例表：
CREATE TABLE table1 (created_on) AS
SELECT SYSDATE - LEVEL FROM DUAL CONNECT BY LEVEL <= 3;
CREATE TABLE table2 (created_on) AS
SELECT SYSDATE - LEVEL FROM DUAL CONNECT BY LEVEL <= 3;
CREATE TABLE "table3" (created_on) AS
SELECT SYSDATE - LEVEL FROM DUAL CONNECT BY LEVEL <= 3;
CREATE TABLE table5 (created_on) AS
SELECT SYSDATE FROM DUAL;
运行在 PL/SQL 块之后，然后：
SELECT * FROM last_dates;
输出：
TABLE_NAME LAST_DATE TABLE1 2021-12-13 13:21:58 TABLE2 2021-12-13 13:21:59 table3 2021-12-13 13:21:59 TABLE5 2021-12-14 13:21:59
db<>fiddle here