Five more things about Oracle SQL and PLSQL

Five things about
SQL and PLSQL
That you might not have known
Thomas Kyte
http://asktom.oracle.com/
Copyright © 2014, Oracle and/or its affiliates. All rights reserved. |

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information purposes only, and may not be incorporated into any contract. It is not a
commitment to deliver any material, code, or functionality, and should not be relied upon
in making purchasing decisions. The development, release, and timing of any features or
functionality described for Oracle’s products remains at the sole discretion of Oracle.

Program Agenda
The optimizer is learning from its mistakes
Functions used, without using a Function
PL/SQL warned you
Location, Location, Location
The most underutilized really cool feature (from five years
ago!)
1
2
3
4
5

tkyte%ORA12C> select /*+ gather_plan_statistics */ count(*)
2 from cities_state
3 where name = 'New York city'
4 and state = 'New York'
5 /
COUNT(*)
----------
8175132

-------------------------------------------------------------
| Id | Operation | Name | E-Rows | A-Rows |
-------------------------------------------------------------
| 0 | SELECT STATEMENT | | | 1 |
| 1 | SORT AGGREGATE | | 1 | 1 |
|* 2 | TABLE ACCESS FULL| CITIES_STATE | 3398 | 8175K|
-------------------------------------------------------------
Predicate Information (identified by operation id):
---------------------------------------------------
2 - filter(("NAME"='New York city' AND "STATE"='New York'))

-------------------------------------------------------------
-------------------------------------------------------------
|* 2 | TABLE ACCESS FULL| CITIES_STATE | 8175K| 8175K|
-------------------------------------------------------------
---------------------------------------------------
2 - filter(("NAME"='New York city' AND "STATE"='New York'))
Note
-----
- statistics feedback used for this statement

tkyte%ORA12C> exec dbms_spd.flush_sql_plan_directive;
PL/SQL procedure successfully completed.
tkyte%ORA12C> select o.object_name, o.subobject_name col_name,
o.object_type, d.type, d.state, d.reason
2 from dba_sql_plan_directives d, dba_sql_plan_dir_objects o
3 where d.directive_id = o.directive_id
4 and o.owner = user
5 order by 1, 2, 3, 4, 5;
OBJECT_NAME COL_NAME OBJECT TYPE STATE REASON
------------ ---------- ------ ---------------- ---------- ------------------------------------
CITIES_STATE NAME COLUMN DYNAMIC_SAMPLING USABLE SINGLE TABLE CARDINALITY MISESTIMATE
CITIES_STATE STATE COLUMN DYNAMIC_SAMPLING USABLE SINGLE TABLE CARDINALITY MISESTIMATE
CITIES_STATE TABLE DYNAMIC_SAMPLING USABLE SINGLE TABLE CARDINALITY MISESTIMATE

tkyte%ORA12C> select /*+ gather_plan_statistics */ count(*)
2 from cities_state
3 where name = 'Los Angeles city'
4 and state = 'California'
5 /
COUNT(*)
----------
3792620

-------------------------------------------------------------
-------------------------------------------------------------
|* 2 | TABLE ACCESS FULL| CITIES_STATE | 5196K| 3792K|
-------------------------------------------------------------
---------------------------------------------------
2 - filter(("NAME"='Los Angeles city' AND "STATE"='California'))
Note
-----
- dynamic statistics used: dynamic sampling (level=2)
- 1 Sql Plan Directive used for this statement

tkyte%ORA12C> select column_name, num_distinct, histogram
2 from user_tab_col_statistics
3 where table_name = 'CITIES_STATE';
COLUMN_NAME NUM_DISTINCT HISTOGRAM
----------- ------------ ---------------
NAME 675 NONE
STATE 50 NONE

tkyte%ORA12C> exec dbms_stats.gather_table_stats(user,'CITIES_STATE');
tkyte%ORA12C> select column_name cname, num_distinct, histogram
2 from user_tab_col_statistics
3 where table_name = 'CITIES_STATE';
CNAME NUM_DISTINCT HISTOGRAM
------------------------------ ------------ ---------------
NAME 675 HYBRID
STATE 50 FREQUENCY
SYS_STS652AVX5KJJE5OOY9V6#UOGP 714 HYBRID

Indexes on Expressions, aka FBI’s
• Available since Oracle 8i
• Index an expression
– Create index I on T(f(x));
• An index used to be used ONLY if the expression that was indexed was
referenced
• Since 11.2.0.2, this has changed…

TKYTE@ORA12C> create table t
2 as
3 select *
4 from all_objects;
Table created.
TKYTE@ORA12C> create index t1_idx on t(substr(object_name,1,10));
Index created.
TKYTE@ORA12C> create index t2_idx on t(trunc(created));
Index created.

TKYTE@ORA12C> select *
2 from t
3 where object_name = '12345678901';
no rows selected
--------------------------------------------------------------
| Id | Operation | Name | Rows |
--------------------------------------------------------------
| 0 | SELECT STATEMENT | | |
|* 1 | TABLE ACCESS BY INDEX ROWID BATCHED| T | 2 |
|* 2 | INDEX RANGE SCAN | T1_IDX | 358 |
--------------------------------------------------------------
---------------------------------------------------
1 - filter("OBJECT_NAME"='12345678901')
2 - access("T"."SYS_NC00019$"='1234567890')

TKYTE@ORA12C> select *
2 from t
3 where created = sysdate;
no rows selected
--------------------------------------------------------------
| Id | Operation | Name | Rows |
--------------------------------------------------------------
| 0 | SELECT STATEMENT | | |
|* 1 | TABLE ACCESS BY INDEX ROWID BATCHED| T | 110 |
|* 2 | INDEX RANGE SCAN | T2_IDX | 358 |
--------------------------------------------------------------
---------------------------------------------------
1 - filter("CREATED"=SYSDATE@!)
2 - access("T"."SYS_NC00020$"=TRUNC(SYSDATE@!))

Warnings
• PL/SQL Compiler has been warning us since 10.1 (2004!)
• Not widely used
• Can be warnings or compile errors

Warnings
• Severe: code might cause unexpected action or wrong results
• Performance: condition might cause performance issues
• Informational: code as written won’t be wrong or slow – just bad
code

TKYTE@ORA12C> alter session set plsql_warnings='enable:severe';
Session altered.
TKYTE@ORA12C> create or replace procedure p
2 as
3 procedure substr
4 is
5 begin
6 null;
7 end;
8 begin
9 null;
10 end;
11 /
SP2-0804: Procedure created with compilation warnings
TKYTE@ORA12C> show errors
Errors for PROCEDURE P:
LINE/COL ERROR
-------- -----------------------------------------------------------------
1/1 PLW-05018: unit P omitted optional AUTHID clause; default value
DEFINER used
3/19 PLW-05004: identifier SUBSTR is also declared in STANDARD or is a
SQL builtin

TKYTE@ORA12C> alter session set plsql_warnings='enable:performance';
Session altered.
2 as
3 l_string varchar2(5);
4 begin
5 for x in (select * from emp where empno = l_string)
6 loop
7 null;
8 end loop;
9 end;
10 /
LINE/COL ERROR
-------- -----------------------------------------------------------------
5/51 PLW-07204: conversion away from column type may result in
sub-optimal query plan

TKYTE@ORA12C> alter session set plsql_warnings='enable:informational';
Session altered.
2 as
3 begin
4 if (null is not null)
5 then
6 dbms_output.put_line( 'hello world' );
7 end if;
8 end;
9 /
LINE/COL ERROR
-------- -----------------------------------------------------------------
6/17 PLW-06002: Unreachable code

TKYTE@ORA12C> alter session set
2 plsql_warnings='enable:all,disable:5018,error:6009,error:7204';
Session altered.
2 as
3 begin
4 dbms_output.put_line( 'hello world' );
5 exception
6 when others
7 then null;
8 end;
9 /
Warning: Procedure created with compilation errors.
LINE/COL ERROR
-------- -----------------------------------------------------------------
6/6 PLS-06009: procedure "P" OTHERS handler does not end in RAISE or
RAISE_APPLICATION_ERROR

TKYTE@ORA12C> alter session set Plsql_Warnings = 'enable:all';
Session altered.
TKYTE@ORA12C> create or replace procedure p authid definer
2 as
3 l_date date := to_date( '01-jan-2011', 'dd-mon-yyyy' );
4 l_start number := dbms_utility.get_cpu_time;
5 begin
6 for x in ( select *
7 from big_table
8 where date_string = l_date )
9 loop
10 null;
11 end loop;
12 dbms_output.put_line( 'CPU: ' ||
13 to_char( dbms_utility.get_cpu_time-l_start ) );
14 end;
15 /

7 from big_table
9 loop
TKYTE@ORA12C> show errors procedure p
LINE/COL ERROR
-------- -----------------------------------------------------------------
TKYTE@ORA12C> exec p
CPU: 69003

TKYTE@ORA12C> create or replace procedure p authid definer
2 as
3 l_date varchar2(15) := '01-jan-2011';
4 l_start number := dbms_utility.get_cpu_time;
5 begin
6 for x in ( select *
7 from big_table
9 loop
10 null;
11 end loop;
12 dbms_output.put_line( 'CPU: ' ||
13 to_char( dbms_utility.get_cpu_time-l_start ) );
14 end;
15 /
Procedure created.
CPU: 343

TKYTE@ORA12C> create table t
2 ( x varchar2(20) constraint t_pk primary key,
3 y varchar2(30)
4 );
Table created.
TKYTE@ORA12C> insert into t
2 select rownum user_id, username
3 from all_users;
39 rows created.

TKYTE@ORA12C> create or replace procedure p authid current_user
2 as
3 l_rec t%rowtype;
4 l_key number := 5;
5 begin
6 select * into l_rec from t where x = l_key;
7 for x in (select plan_table_output
8 from TABLE( dbms_xplan.display_cursor() ) )
9 loop
10 dbms_output.put_line( x.plan_table_output );
11 end loop;
12 end;
13 /

5 begin
LINE/COL ERROR
-------- -----------------------------------------------------------------

SQL_ID 18796jgha0hwz, child number 0
-------------------------------------
SELECT * FROM T WHERE X = :B1
Plan hash value: 1601196873
---------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)|
---------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 3 (100)|
|* 1 | TABLE ACCESS FULL| T | 1 | 29 | 3 (0)|
---------------------------------------------------------------
---------------------------------------------------
1 - filter(TO_NUMBER("X")=:B1)

2 as
3 l_rec t%rowtype;
4 l_key varchar2(5) := '5';
5 begin
9 loop
10 dbms_output.put_line( x.plan_table_output );
11 end loop;
12 end;
13 /
Procedure created.

SQL_ID 18796jgha0hwz, child number 1
-------------------------------------
SELECT * FROM T WHERE X = :B1
Plan hash value: 1303508680
------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes |
------------------------------------------------------------
| 0 | SELECT STATEMENT | | | |
| 1 | TABLE ACCESS BY INDEX ROWID| T | 1 | 29 |
|* 2 | INDEX UNIQUE SCAN | T_PK | 1 | |
------------------------------------------------------------
---------------------------------------------------
2 - access("X"=:B1)

TKYTE@ORA12C> CREATE TABLE t
2 (
3 dt date,
4 x int,
5 y varchar2(30)
6 )
7 PARTITION BY RANGE (dt)
8 (
9 PARTITION part1 VALUES
LESS THAN(to_date('31-jan-2011', 'dd-mon-yyyy')),
10 PARTITION part2 VALUES
LESS THAN(to_date('28-feb-2011', 'dd-mon-yyyy'))
11 )
12 /
Table created.

2 as
3 l_date timestamp := timestamp'2011-01-15 00:00:00.000';
4 l_count number;
5 begin
6 select count(*) into l_count from t where dt = l_date;
7
10 loop
11 dbms_output.put_line( '.'||x.plan_table_output );
12 end loop;
13 end;
14 /

5 begin
7
LINE/COL ERROR
-------- -----------------------------------------------------------------

.SQL_ID 0t5m83d3m67q7, child number 1
.-------------------------------------
.SELECT COUNT(*) FROM T WHERE DT = :B1
.
.Plan hash value: 3225603066
.
.---------------------------------------------------------------------
.| Id | Operation | Name | Rows | Bytes | Pstart| Pstop |
.---------------------------------------------------------------------
.| 0 | SELECT STATEMENT | | | | | |
.| 1 | SORT AGGREGATE | | 1 | 9 | | |
.| 2 | PARTITION RANGE ALL| | 1 | 9 | 1 | 2 |
.|* 3 | TABLE ACCESS FULL | T | 1 | 9 | 1 | 2 |
.---------------------------------------------------------------------
.
.Predicate Information (identified by operation id):
.---------------------------------------------------
.
. 3 - filter(INTERNAL_FUNCTION("DT")=:B1)

2 as
3 l_date date := to_date( '2011-01-15', 'yyyy-mm-dd' );
4 l_count number;
5 begin
7
10 loop
11 dbms_output.put_line( '.'||x.plan_table_output );
12 end loop;
13 end;
14 /
Procedure created.

.SQL_ID 0t5m83d3m67q7, child number 2
.-------------------------------------
.SELECT COUNT(*) FROM T WHERE DT = :B1
.
.Plan hash value: 3660200434
.
.------------------------------------------------------------------------
.| Id | Operation | Name | Rows | Bytes | Pstart| Pstop |
.------------------------------------------------------------------------
.| 0 | SELECT STATEMENT | | | | | |
.| 1 | SORT AGGREGATE | | 1 | 9 | | |
.| 2 | PARTITION RANGE SINGLE| | 1 | 9 | KEY | KEY |
.|* 3 | TABLE ACCESS FULL | T | 1 | 9 | KEY | KEY |
.------------------------------------------------------------------------
.
.Predicate Information (identified by operation id):
.---------------------------------------------------
. 3 - filter("DT"=:B1)

TKYTE@ORA12C> alter session set Plsql_Warnings = 'error:all';
Session altered.

Warnings
• Can be set at
– The system level ALTER SYSTEM
– The session level ALTER SESSION
– Unit by unit
ALTER PROCEDURE P COMPILE PLSQL_WARNINGS=‘…’ REUSE
SETTINGS;

How your data is organized impacts the plan
• Empno, Hiredate and Ename – what is different about the way they arrive?
• An index on Empno or Hiredate would typically be used to retrieve many
more rows from the table then an index on Ename
• There are various techniques we can employ to “cluster” data differently
• Let’s look at the clustering factor first…

TKYTE@ORA12C> create table t1
2 as
3 select chr( ascii('A')+mod(rownum,26) ) ||
to_char(rownum, 'fm00000') key,
4 rpad( 'x', 260, 'x') data
5 from all_objects
6 where rownum <= 26*40;
Table created.
TKYTE@ORA12C> alter table t1 modify (key not null);
Table altered.
TKYTE@ORA12C> create index t1_idx on t1(key);
Index created.

TKYTE@ORA12C> create table t2
2 as
3 select key, data
4 from t1
5 order by key;
Table created.
TKYTE@ORA12C> create index t2_idx on t2(key);
Index created.

TKYTE@ORA12C> select min(cnt), max(cnt), avg(cnt)
2 from (
3 select bno, count(*) cnt
4 from (
5 select dbms_rowid.rowid_block_number( rowid ) bno
6 from t1 /* or t2! */
7 )
8 group by bno
9 )
10 /
MIN(CNT) MAX(CNT) AVG(CNT)
---------- ---------- ----------
26 26 26

TKYTE@ORA12C> select table_name, blocks, num_rows,
to_char(last_analyzed,'dd-mon hh24:mi:ss') la
2 from user_tables
3 where table_name in ('T1','T2')
4 order by 1;
TABLE_NAME BLOCKS NUM_ROWS LA
-------------------- ---------- ---------- ------------------------
T1 45 1040 25-sep 17:34:33
T2 45 1040 25-sep 17:34:33
TKYTE@ORA12C> select table_name, index_name, clustering_factor,
2 from user_indexes
4 order by 1;
TABLE_NAME INDEX_NAME CLUSTERING_FACTOR LA
-------------------- -------------------- ----------------- ----------------
T1 T1_IDX 1040 25-sep 17:34:33
T2 T2_IDX 40 25-sep 17:34:33

TKYTE@ORA12C> select /*+ index( t1 t1_idx ) */ count(data)
2 from t1;
COUNT(DATA)
-----------
1040
TKYTE@ORA12C> select /*+ index( t2 t2_idx ) */ count(data)
2 from t2;
COUNT(DATA)
-----------
1040

select /*+ index( t1 t1_idx ) */ count(data)
from t1
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 1044 0 1
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 0.00 0.00 0 1044 0 1
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 103
Number of plan statistics captured: 1
Rows (1st) Rows (avg) Rows (max) Row Source Operation
---------- ---------- ---------- ----------------------------------------------
1 1 1 SORT AGGREGATE (cr=1044 pr=0 pw=0 time=1920 us
1040 1040 1040 TABLE ACCESS BY INDEX ROWID BATCHED T1 (cr=10
1040 1040 1040 INDEX FULL SCAN T1_IDX (cr=4 pr=0 pw=0 time=
1044-4 = 1040, the clustering factor of T1_IDX

select /*+ index( t2 t2_idx ) */ count(data)
from t2
call count cpu elapsed disk query current rows
------- ------ -------- ---------- ---------- ---------- ---------- ----------
Parse 1 0.00 0.00 0 0 0 0
Execute 1 0.00 0.00 0 0 0 0
Fetch 2 0.00 0.00 0 44 0 1
------- ------ -------- ---------- ---------- ---------- ---------- ----------
total 4 0.00 0.00 0 44 0 1
Misses in library cache during parse: 1
Optimizer mode: ALL_ROWS
Parsing user id: 103
Number of plan statistics captured: 1
Rows (1st) Rows (avg) Rows (max) Row Source Operation
---------- ---------- ---------- ----------------------------------------------
1 1 1 SORT AGGREGATE (cr=44 pr=0 pw=0 time=1004 us)
1040 1040 1040 TABLE ACCESS BY INDEX ROWID BATCHED T2 (cr=44
1040 1040 1040 INDEX FULL SCAN T2_IDX (cr=4 pr=0 pw=0 time=
44-4 = 40, the clustering factor of T2_IDX

TKYTE@ORA12C> select count(data)
2 from t1
3 where key between 'A00000' and 'A00250';
COUNT(DATA)
-----------
9
TKYTE@ORA12C> select * from table(dbms_xplan.display_cursor);
------------------------------------------------------------------------------------
------------------------------------------------------------------------------------
| 1 | SORT AGGREGATE | | 1 | 268 | |
| 2 | TABLE ACCESS BY INDEX ROWID BATCHED| T1 | 9 | 2412 | 12 (0)|
|* 3 | INDEX RANGE SCAN | T1_IDX | 9 | | 2 (0)|
------------------------------------------------------------------------------------
---------------------------------------------------
3 - access("KEY">='A00000' AND "KEY"<='A00250')

2 from t2
COUNT(DATA)
-----------
9
------------------------------------------------------------------------------------
------------------------------------------------------------------------------------
| 1 | SORT AGGREGATE | | 1 | 268 | |
------------------------------------------------------------------------------------
---------------------------------------------------

2 from t1
COUNT(DATA)
-----------
19
---------------------------------------------------------------------------
| Id | Operation | Name | Rows | Bytes | Cost (%CPU)| Time |
---------------------------------------------------------------------------
| 0 | SELECT STATEMENT | | | | 14 (100)| |
| 1 | SORT AGGREGATE | | 1 | 268 | | |
|* 2 | TABLE ACCESS FULL| T1 | 20 | 5360 | 14 (0)| 00:00:01 |
---------------------------------------------------------------------------
---------------------------------------------------
2 - filter(("KEY"<='A00500' AND "KEY">='A00000'))

2 from t2
COUNT(DATA)
-----------
19
------------------------------------------------------------------------------------
------------------------------------------------------------------------------------
| 1 | SORT AGGREGATE | | 1 | 268 | |
------------------------------------------------------------------------------------
---------------------------------------------------

TKYTE@ORA12C> begin
2 dbms_stats.set_table_prefs
3 ( ownname => user,
4 tabname => 'T1',
5 pname => 'TABLE_CACHED_BLOCKS',
6 pvalue => 42 );
7 dbms_stats.set_table_prefs
8 ( ownname => user,
9 tabname => 'T2',
10 pname => 'TABLE_CACHED_BLOCKS',
11 pvalue => 42 );
12
13 dbms_stats.gather_index_stats( user, 'T1_IDX' );
14 dbms_stats.gather_index_stats( user, 'T2_IDX' );
15 end;
16 /

TKYTE@ORA12C> select table_name, index_name, clustering_factor,
2 from user_indexes
4 order by 1;
TABLE_NAME INDEX_NAME CLUSTERING_FACTOR LA
-------------------- -------------------- ----------------- ---------------
T1 T1_IDX 40 25-sep 17:34:36
T2 T2_IDX 40 25-sep 17:34:36

Quick Story…
I’m going to write a PL/SQL parser…

TKYTE%ORA12C> create user demo
2 identified by demo;
User created.
TKYTE%ORA12C> grant create session,
2 create procedure
3 to demo;
Grant succeeded.
TKYTE%ORA12C> create edition version2
2 as child of ora$base;
Edition created.

TKYTE%ORA12C> connect demo/demo
Connected.
DEMO%ORA12C> create or replace
2 procedure my_procedure
3 as
4 begin
5 dbms_output.put_line( 'I am buggy version 1.0' );
6 end;
7 /
Procedure created.
2 procedure my_procedure2
3 as
4 begin
5 my_procedure;
6 end;
7 /
Procedure created.

DEMO%ORA12C> exec my_procedure2
I am buggy version 1.0

DEMO%ORA12C> alter session
2 set edition = version2;
ERROR:
ORA-38802: edition does not exist

DEMO%ORA12C> connect tkyte/tkyte
Connected.
TKYTE%ORA12C> alter user demo
2 enable editions;
User altered.
TKYTE%ORA12C> grant use
2 on edition version2
3 to demo;
Grant succeeded.
TKYTE%ORA12C> grant use
2 on edition version2
3 to scott;
Grant succeeded.

TKYTE%ORA12C> connect demo/demo
Connected.
DEMO%ORA12C> alter session
Session altered.
DEMO%ORA12C> select object_name, object_type, status, edition_name
2 from user_objects;
OBJECT_NAME OBJECT_TYPE STATUS EDITION_NAME
------------------------------ ----------- ------ ------------
MY_PROCEDURE PROCEDURE VALID ORA$BASE
MY_PROCEDURE2 PROCEDURE VALID ORA$BASE

2 procedure my_procedure
3 as
4 begin
5 dbms_output.put_line( 'I am fixed in version 2.0' );
6 end;
7 /
Procedure created.

DEMO%ORA12C> select object_name, edition_name
2 from user_objects;
OBJECT_NAME EDITION_NAME
------------------------------ ------------
MY_PROCEDURE2 ORA$BASE
MY_PROCEDURE VERSION2
DEMO%ORA12C> select object_name, edition_name
2 from user_objects_AE;
------------------------------ ------------
MY_PROCEDURE ORA$BASE

DEMO%ORA12C> grant execute on my_procedure2 to scott;
Grant succeeded.
DEMO%ORA12C> select object_name, edition_name from user_objects;
------------------------------ ------------
MY_PROCEDURE2 VERSION2
DEMO%ORA12C> select object_name, edition_name from user_objects_AE;
------------------------------ ------------
MY_PROCEDURE ORA$BASE
MY_PROCEDURE2 VERSION2

DEMO%ORA12C> SELECT SYS_CONTEXT ('userenv', 'current_edition_name') sc
2 FROM DUAL;
SC
---------------
VERSION2
I am fixed in version 2.0

DEMO%ORA12C> connect demo/demo
Connected.
2 FROM DUAL;
SC
---------------
ORA$BASE
I am buggy version 1.0

DEMO%ORA12C> alter session set edition = version2;
Session altered.
2 FROM DUAL;
SC
---------------
VERSION2

DEMO%ORA12C> connect scott/tiger
Connected.
SCOTT%ORA12C> SELECT SYS_CONTEXT ('userenv', 'current_edition_name') sc
2 FROM DUAL;
SC
---------------
ORA$BASE
SCOTT%ORA12C> exec demo.my_procedure2
BEGIN demo.my_procedure2; END;
*
ERROR at line 1:
ORA-06550: line 1, column 7:
PLS-00201: identifier 'DEMO.MY_PROCEDURE2' must be declared
ORA-06550: line 1, column 7:
PL/SQL: Statement ignored

SCOTT%ORA12C> alter session
Session altered.
SCOTT%ORA12C> exec demo.my_procedure2

Five more things about Oracle SQL and PLSQL

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