I'm relatively new to the PostgreSQL environment, coming from years of experience in SQLServer. Not sure if this is an environmental thing with pgAdmin or just PostgreSQL itself but I'm wondering how to preserve comments in saved SQL statements.
For example, say you create a view like
create view MyView
as
/*
comment1
comment2
...
*/
select col1
,col2
--,col3 -- comment line
from tbl1
where 1 = 1;
and then highlight this created view in pgAdmin (in the object browser), none of those comments appear. You basically see something like
create or replace view myview as
select col1,
col2
from tbl1
where 1 = 1;
As you can see, the comments have been removed. Is this a config setting, am I "doing it wrong"?
Many thanks,
B
Related
In T-SQL I used to debug in script or stored procedure like below (very simple example), to check the data of the tables :
declare #my_variable nvarchar(4) = 'test';
....
update t
set t.my_column = case when t.my_column_3 = 1
then 1 + 1
when t.my_column_4 = 2
then 2 + 2
...
end
from my_table t
where t.column_2 = 'test';
--check the updated data
select t.my_column, t.my_column_2, t.my_column_3, t.my_column_4
from my_table t
where t.column_2 = 'test';
update t
set t.my_column_5 = case when t.my_column_6 + t.my_column_7 = t.my_column_8
then 'OK'
else 'NOT OK'
end,
....
from my_table t
where t.column_2 = 'test_2';
--check the updated data
select t.my_column_5, t.my_column_6, t.my_column_7, t.my_column_8
from my_table t
where t.column_2 = 'test_2';
etc..
I know that in Oracle is quite different but is there a similar way to check the data of some tables in a middle of a pl/sql script.
I did some research and apparently we can use dbms_output but it's not as simple as a select * from my_table like in T-SQL.
Also sometimes, after running a pl/sql script (manipulate the data etc), I need to display the datas of two or more tables in my script (for controlling purpose) is it possible ?
All suggestions are welcome.
Thank you.
Is there a hint to generate execution plan ignoring the existing one from the shared pool?
There is not a hint to create an execution plan that ignores plans in the shared pool. A more common way of phrasing this question is: how do I get Oracle to always perform a hard parse?
There are a few weird situations where this behavior is required. It would be helpful to fully explain your reason for needing this, as the solution varies depending why you need it.
Strange performance problem. Oracle performs some dynamic re-optimization of SQL statements after the first run, like adaptive cursor sharing and cardinality feedback. In the rare case when those features backfire you might want to disable them.
Dynamic query. You have a dynamic query that used Oracle data cartridge to fetch data in the parse step, but Oracle won't execute the parse step because the query looks static to Oracle.
Misunderstanding. Something has gone wrong and this is an XY problem.
Solutions
The simplest way to solve this problem are by using Thorsten Kettner's solution of changing the query each time.
If that's not an option, the second simplest solution is to flush the query from the shared pool, like this:
--This only works one node at a time.
begin
for statements in
(
select distinct address, hash_value
from gv$sql
where sql_id = '33t9pk44udr4x'
order by 1,2
) loop
sys.dbms_shared_pool.purge(statements.address||','||statements.hash_value, 'C');
end loop;
end;
/
If you have no control over the SQL, and need to fix the problem using a side-effect style solution, Jonathan Lewis and Randolf Geist have a solution using Virtual Private Database, that adds a unique predicate to each SQL statement on a specific table. You asked for something weird, here's a weird solution. Buckle up.
-- Create a random predicate for each query on a specific table.
create table hard_parse_test_rand as
select * from all_objects
where rownum <= 1000;
begin
dbms_stats.gather_table_stats(null, 'hard_parse_test_rand');
end;
/
create or replace package pkg_rls_force_hard_parse_rand is
function force_hard_parse (in_schema varchar2, in_object varchar2) return varchar2;
end pkg_rls_force_hard_parse_rand;
/
create or replace package body pkg_rls_force_hard_parse_rand is
function force_hard_parse (in_schema varchar2, in_object varchar2) return varchar2
is
s_predicate varchar2(100);
n_random pls_integer;
begin
n_random := round(dbms_random.value(1, 1000000));
-- s_predicate := '1 = 1';
s_predicate := to_char(n_random, 'TM') || ' = ' || to_char(n_random, 'TM');
-- s_predicate := 'object_type = ''TABLE''';
return s_predicate;
end force_hard_parse;
end pkg_rls_force_hard_parse_rand;
/
begin
DBMS_RLS.ADD_POLICY (USER, 'hard_parse_test_rand', 'hard_parse_policy', USER, 'pkg_rls_force_hard_parse_rand.force_hard_parse', 'select');
end;
/
alter system flush shared_pool;
You can see the hard-parsing in action by running the same query multiple times:
select * from hard_parse_test_rand;
select * from hard_parse_test_rand;
select * from hard_parse_test_rand;
select * from hard_parse_test_rand;
Now there are three entries in GV$SQL for each execution. There's some odd behavior in Virtual Private Database that parses the query multiple times, even though the final text looks the same.
select *
from gv$sql
where sql_text like '%hard_parse_test_rand%'
and sql_text not like '%quine%'
order by 1;
I think there is no hint indicating that Oracle shall find a new execution plan everytime it runs the query.
This is something we'd want for select * from mytable where is_active = :active, with is_active being 1 for very few rows and 0 for maybe billions of other rows. We'd want an index access for :active = 1 and a full table scan for :active = 0 then. Two different plans.
As far as I know, Oracle uses bind variable peeking in later versions, so with a look at the statistics it really comes up with different execution plans for different bind varibale content. But in older versions it did not, and thus we'd want some hint saying "make a new plan" there.
Oracle only re-used an execution plan for exactly the same query. It sufficed to add a mere blank to get a new plan. Hence a solution might be to generate the query everytime you want to run it with a random number included in a comment:
select /* 1234567 */ * from mytable where is_active = :active;
Or just don't use bind variables, if this is the problem you want to address:
select * from mytable where is_active = 0;
select * from mytable where is_active = 1;
I've a normal select:
e = session.query(MyTable).filter(MyTable.pk=='abc').all()
Where MyTable is mapped to my_table in db.
I've also created a derived view my_view in database that has the exact same named columns as my_table.
Is there a way to substitute in my_view for my_table at query time so that I get back rows from the view? Obviously the resulting objects would need to be read only - am not intending to alter them.
So basically I'd want the SQL to be
FROM my_view AS my_table
instead of
FROM my_table
With everything else the same in the query.
I'd prefer not to create another mapper unless it can be done automatically somehow as MyView has over 60 columns same as MyTable.
Update: select_entity_from seems to be what I need, but in this case it just adds to the FROM tables, instead of replacing:
v = Table('my_view', metadata, autoload=True)
print session.query(MyTable).select_entity_from(v).filter(MyTable.pk=='abc')
"SELECT ... FROM my_table, my_view WHERE my_table.pk = 'abc';"
But the following only has one FROM entity:
print session.query(MyTable).\
select_entity_from(select([MyTable])).\
filter(MyTable.pk=='abc')
"SELECT ... FROM (SELECT ... FROM my_tabl) AS anon_1 WHERE anon_1.pk = 'abc';"
Further digging has got me closer to the answer but no joy. Posting progress here in case it solicits further thoughts:
from sqlalchemy.orm.util import aliased
session.query(MyTable).select_entity_from(
select([aliased(MyTable, alias=v, adapt_on_names=True)])).\
filter(MyTable.pk=='abc')
adapt_on_names seems to be what I need, and I've double checked that the view has the exact same column names as the table, but the above still produces two froms.
Filed what I thought was a bug: https://bitbucket.org/zzzeek/sqlalchemy/issues/3933/allow-passing-aliased-to
Final answer was:
session.query(MyTable).select_entity_from(
text('SELECT * FROM my_view').columns(*MyTable.__table__.columns)).\
filter(MyTable.pk=='abc')
Using h2 in embedded mode, I am restoring an in memory database from a script backup that was previously generated by h2 using the SCRIPT command.
I use this URL:
jdbc:h2:mem:main
I am doing it like this:
FileReader script = new FileReader("db.sql");
RunScript.execute(conn,script);
which, according to the doc, should be similar to this SQL:
RUNSCRIPT FROM 'db.sql'
And, inside my app they do perform the same. But if I run the load using the web console using h2.bat, I get a different result.
Following the load of this data in my app, there are rows that I know are loaded but are not accessible to me via a query. And these queries demonstrate it:
select count(*) from MY_TABLE yields 96576
select count(*) from MY_TABLE where ID <> 3238396 yields 96575
select count(*) from MY_TABLE where ID = 3238396 yields 0
Loading the web console and using the same RUNSCRIPT command and file to load yields a database where I can find the row with that ID.
My first inclination was that I was dealing with some sort of locking issue. I have tried the following (with no change in results):
manually issuing a conn.commit() after the RunScript.execute()
appending ;LOCK_MODE=3 and the ;LOCK_MODE=0 to my URL
Any pointers in the right direction on how I can identify what is going on? I ended up inserting :
Server.createWebServer("-trace","-webPort","9083").start()
So that I could run these queries through the web console to sanity check what was coming back through JDBC. The problem happens consistently in my app and consistently doesn't happen via the web console. So there must be something at work.
The table schema is not exotic. This is the schema column from
select * from INFORMATION_SCHEMA.TABLES where TABLE_NAME='MY_TABLE'
CREATE MEMORY TABLE PUBLIC.MY_TABLE(
ID INTEGER SELECTIVITY 100,
P_ID INTEGER SELECTIVITY 4,
TYPE VARCHAR(10) SELECTIVITY 1,
P_ORDER DECIMAL(8, 0) SELECTIVITY 11,
E_GROUP INTEGER SELECTIVITY 1,
P_USAGE VARCHAR(16) SELECTIVITY 1
)
Any push in the right direction would be really appreciated.
EDIT
So it seems that the database is corrupted in some way just after running the RunScript command to load it. As I was trying to debug to find out what is going on, I tried executing the following:
delete from MY_TABLE where ID <> 3238396
And I ended up with:
Row not found when trying to delete from index "PUBLIC.MY_TABLE_IX1: 95326", SQL statement:
delete from MY_TABLE where ID <> 3238396 [90112-178] 90112/90112 (Help)
I then tried dropping and recreating all my indexes from within the context, but it had no effect on the overall problem.
Help!
EDIT 2
More information: The problem occurs due to the creation of an index. (I believe I have found a bug in h2 and I have working on creating a minimal case that reproduces it). The simple code below will reproduce the problem, if you have the right set of data.
public static void main(String[] args)
{
try
{
final String DB_H2URL = "jdbc:h2:mem:main;LOCK_MODE=3";
Class.forName("org.h2.Driver");
Connection c = DriverManager.getConnection(DB_H2URL, "sa", "");
FileReader script = new FileReader("db.sql");
RunScript.execute(c,script);
script.close();
Statement st = c.createStatement();
ResultSet rs = st.executeQuery("select count(*) from MY_TABLE where P_ID = 3238396");
rs.next();
if(rs.getLong(1) == 0)
System.err.println("It happened");
else
System.err.println("It didn't happen");
} catch (Throwable e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
I have reduced the db.sql script to about 5000 rows and it still happens. When I attempted to go to 2500 rows, it stopped happening. If I remove the last line of the db.sql (which is the index creation), the problem will also stop happening. The last line is this:
CREATE INDEX PUBLIC.MY_TABLE_IX1 ON PUBLIC.MY_TABLE(P_ID);
But the data is an important player in this. It still appears to only ever be the one row and the index somehow makes it inaccessible.
EDIT 3
I have identified the minimal data example to reproduce. I stripped the table schema down to a single column, and I found that the values in that column don't seem to matter -- just the number of rows. Here is the contents of (snipped with obvious stuff) of my db.sql generated via the SCRIPT command:
;
CREATE USER IF NOT EXISTS SA SALT '8eed806dbbd1ea59' HASH '6d55cf715c56f4ca392aca7389da216a97ae8c9785de5d071b49de5436b0c003' ADMIN;
CREATE MEMORY TABLE PUBLIC.MY_TABLE(
P_ID INTEGER SELECTIVITY 100
);
-- 5132 +/- SELECT COUNT(*) FROM PUBLIC.MY_TABLE;
INSERT INTO PUBLIC.MY_TABLE(P_ID) VALUES
(1),
(2),
(3),
... snipped you obviously have breaks in the bulk insert here ...
(5143),
(3238396);
CREATE INDEX PUBLIC.MY_TABLE_IX1 ON PUBLIC.MY_TABLE(P_ID);
But that will recreate the problem. [Note that my numbering skips a number every time there was a bulk insert line. So there really is 5132 rows, though you see 5143 select count(*) from MY_TABLE yields 5132]. Also, I seem to be able to recreate the problem in the WebConsole directly now by doing:
drop table MY_TABLE
runscript from 'db.sql'
select count(*) from MY_TABLE where P_ID = 3238396
You have recreated the problem if you get 0 back from the select when you know you have a row in there.
Oddly enough, I seem to be able to do
select * from MY_TABLE order by P_ID desc
and I can see the row at this point. But going directly for the row:
select * from MY_TABLE where P_ID = 3238396
Yields nothing.
I just realized that I should note that I am using h2-1.4.178.jar
The h2 folks have already apparently resolved this.
https://code.google.com/p/h2database/issues/detail?id=566
Just either need to get the code from version control or wait for the next release build. Thanks Thomas.
A weird request maybe but. My boss wants me to create an admin version of a page we have that displays data from an oracle query in a table.
The admin page, instead of displaying the data (query returns 1 row), needs to return the table name and column name
Ex: Instead of:
Name Initial
==================
Bob A
I want:
Name Initial
============================
Users.FirstName Users.MiddleInitial
I realize I can do this in code but would rather just modify the query to return the data I want so I can leave the report generation code mostly alone.
I don't want to do it in a stored procedure.
So when I spit out the data in the report using something like:
blah blah = MyDataRow("FirstName")
I can leave that as is but instead of it displaying "BOB" it would display "Users.FirstName"
And I want to do the query using select * if possible instead of listing all the columns
So for each of the columns I am querying in the * , I want to get (instead of the column value) the tablename.ColumnName or tablename|columnName
hope you are following- I am confusing myself...
pseudo:
select tablename + '.' + Columnname as WhateverTheColumnNameIs
from Table1
left join Table2 on whatever...
Join Table_Names on blah blah
Whew- after writing all this I think I will just do it on the code side.
But if you are up for it maybe a fun challenge
Oracle does not provide an authentic way(there is no pseudocolumn) to get the column name of a table as a result of a query against that table. But you might consider these two approaches:
Extract column name from an xmltype, formed by passing cursor expression(your query) in the xmltable() function:
-- your table
with t1(first_name, middle_name) as(
select 1,2 from dual
), -- your query
t2 as(
select * -- col1 as "t1.col1"
--, col2 as "t1.col2"
--, col3 as "t1.col3"
from hr.t1
)
select *
from ( select q.object_value.getrootelement() as col_name
, rownum as rn
from xmltable('//*'
passing xmltype(cursor(select * from t2 where rownum = 1))
) q
where q.object_value.getrootelement() not in ('ROWSET', 'ROW')
)
pivot(
max(col_name) for rn in (1 as "name", 2 as "initial")
)
Result:
name initial
--------------- ---------------
FIRST_NAME MIDDLE_NAME
Note: In order for column names to be prefixed with table name, you need to list them
explicitly in the select list of a query and supply an alias, manually.
PL/SQL approach. Starting from Oracle 11g you could use dbms_sql() package and describe_columns() procedure specifically to get the name of columns in the cursor(your select).
This might be what you are looking for, try selecting from system views USER_TAB_COLS or ALL_TAB_COLS.