I have a simple table with one column of numbers. I want to load about 3000 numbers in it. I want to do that in memory, without using SQL*Loader. I tried
INSERT ALL
INTO t_table (code) VALUES (n1)
INTO t_table (code) VALUES (n2)
...
...
INTO t_table (code) VALUES (n3000)
SELECT * FROM dual
But I fails at 1000 values. What should I do ? Is SQL*Loader the only way ? Can I do LOAD with SQL only ?
Presumably you have an initial value of n. If so, this code will populate code with values n to n+2999 :
insert into t_table (code)
select (&N + level ) - 1
from dual
connect by level <=3000
This query uses a SQL*Plus substitution variable to post the initial value of n. Other clients will need to pass the value in a different way.
"Assume that I am in c++ with a stl::vector, what query should I
write ?"
So when you wrote n3000 what you really meant was n(3000). It's easy enough to use an array in SQL. This example uses one of Oracle's pre-defined collections, a table of type NUMBER:
declare
ids system.number_tbl_type;
begin
insert into t_table (code)
select column_value
from table ( select ids from dual )
;
end;
As for mapping your C++ vector to Oracle types, that's a different question (and one which I can't answer).
Related
Given the following example:
BEGIN
FOR r IN (
SELECT * FROM table_one WHERE change_id = 0
) LOOP
r.change_id := -1;
INSERT INTO table_one VALUES r;
END LOOP;
END;
This inserts new rows to table_one with the exact same content, except the intended change on column change_id to the value -1. I don't have to specify the columns inside of the script as I have to in an INSERT INTO table_one (change_id, ...) SELECT -1, ... FROM table_one WHERE change_id=0;
It works perfectly fine. But how to modify this script to work with a list of tables? The internal structure of those tables are different, but all of them have the necessary column change_id.
Of course the easiest solution would be to copy and paste this snippet x-times and replace the fix table name inside. But is there an option to work with a list of tables in an array?
My approach was like this:
DECLARE
TYPE tablenamearray IS VARRAY(30) OF VARCHAR2(30);
tablenames tablenamearray;
BEGIN
tablenames := tablenamearray('TABLE_ONE', 'TABLE_TWO', 'TABLE_THREE'); -- up to table 30...
FOR i IN tablenames.first..tablenames.last LOOP
/* Found no option to use tablenames(i) here with dynamic SQL */
END LOOP;
END;
Note: There is no technical primary key like an id with a sequence behind. The primary key is build by three columns incl. the change_id column.
You cannot create a SQL statement where the statement is not known at parse time. So, you cannot have a variable as a table name. What you're looking for is Dynamic SQL, which is a fairly complicated topic, but basically you're going to wind up building a SQL statement with DBMS_SQL or running a statement as a string with EXECUTE IMMEDIATE.
I'm playing around with array support in Oracle and hit a roadblock regarding array access within a SQL query. I'm using the following schema:
create type smallintarray as varray(10) of number(3,0);
create table tbl (
id number(19,0) not null,
the_array smallintarray,
primary key (id)
);
What I would like to do is get the id and the first element i.e. at index 1 of the array. In PostgreSQL I could write select id, the_array[1] from tbl t but I don't see how I could do that with Oracle. I read that array access by index is only possible in PL/SQL, which would be fine if I could return a "decorated cursor" to achieve the same result through JDBC, but I don't know if that's possible.
DECLARE
c1 SYS_REFCURSOR;
varr smallintarray2;
BEGIN
OPEN c1 FOR SELECT t.id, t.THE_ARRAY from tbl t;
-- SELECT t.THE_ARRAY INTO varr FROM table_with_enum_arrays2 t;
-- return a "decorated cursor" with varr(1) at select item position 1
dbms_sql.return_result(c1);
END;
You can do this in plain SQL; it's not pretty, but it does work. You would prefer that Oracle had syntax to hide this from the programmer (and perhaps it does, at least in the most recent versions; I am still stuck at 12.2).
select t.id, q.array_element
from tbl t cross apply
( select column_value as array_element,
rownum as ord
from table(the_array)
) q
where ord = 1
;
EDIT If order of generating the elements through the table operator is a concern, you could do something like this (in Oracle 12.1 and higher; otherwise the function can't be part of the query itself, but it can be defined on its own):
with
function select_element(arr smallintarray, i integer)
return number
as
begin
return arr(i);
end;
select id, select_element(the_array, 1) as the_array_1
from tbl
/
First of all, please don't do that on production. Use tables instead of storing arrays within a table.
Answer to your question is to use column as a table source
SELECT t.id, ta.*
from tbl t,
table(t.THE_ARRAY) ta
order by column_value
-- offset 1 row -- in case if sometime you'll need to skip a row
fetch first 1 row only;
UPD: as for ordering the array I can only say playing with 2asc/desc" parameters provided me with results I've expected - it has been ordered ascending or descending.
UPD2: found a cool link to description of performance issues might happen
I have function which returns column names and i am trying to use the column name as part of my select statement, but my results are coming as column name instead of values
FUNCTION returning column name:
get_col_name(input1, input2)
Can И use this query to the results of the column from table -
SELECT GET_COL_NAME(input1,input2) FROM TABLE;
There are a few ways to run dynamic SQL directly inside a SQL statement. These techniques should be avoided since they are usually complicated, slow, and buggy. Before you do this try to find another way to solve the problem.
The below solution uses DBMS_XMLGEN.GETXML to produce XML from a dynamically created SQL statement, and then uses XML table processing to extract the value.
This is the simplest way to run dynamic SQL in SQL, and it only requires built-in packages. The main limitation is that the number and type of columns is still fixed. If you need a function that returns an unknown number of columns you'll need something more powerful, like the open source program Method4. But that level of dynamic code gets even more difficult and should only be used after careful consideration.
Sample schema
--drop table table1;
create table table1(a number, b number);
insert into table1 values(1, 2);
commit;
Function that returns column name
create or replace function get_col_name(input1 number, input2 number) return varchar2 is
begin
if input1 = 0 then
return 'a';
else
return 'b';
end if;
end;
/
Sample query and result
select dynamic_column
from
(
select xmltype(dbms_xmlgen.getxml('
select '||get_col_name(0,0)||' dynamic_column from table1'
)) xml_results
from dual
)
cross join
xmltable
(
'/ROWSET/ROW'
passing xml_results
columns dynamic_column varchar2(4000) path 'DYNAMIC_COLUMN'
);
DYNAMIC_COLUMN
--------------
1
If you change the inputs to the function the new value is 2 from column B. Use this SQL Fiddle to test the code.
I'm trying to use a nested table inside the IN clause in a PL-SQL block.
First, I have defined a TYPE:
CREATE OR REPLACE TYPE VARCHAR_ARRAY AS TABLE OF VARCHAR2(32767);
Here is my PL-SQL block using the 'BULK COLLECT INTO':
DECLARE
COL1 VARCHAR2(50) := '123456789';
N_TBL VARCHAR_ARRAY := VARCHAR_ARRAY();
C NUMBER;
BEGIN
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('START: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
SELECT COLUMN1
BULK COLLECT INTO N_TBL
FROM MY_TABLE
WHERE COLUMN1 = COL1;
SELECT COUNT(COLUMN1)
INTO C
FROM MY_OTHER_TABLE
WHERE COLUMN1 IN (SELECT column_value FROM TABLE(N_TBL));
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('ENDED: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
END;
And the output is:
START: 01-08-2014 12:36:14.997
ENDED: 01-08-2014 12:36:17.554
It takes more than 2.5 seconds (2.557 seconds exactly)
Now, If I replace the nested table by a subquery, like this:
DECLARE
COL1 VARCHAR2(50) := '123456789';
N_TBL VARCHAR_ARRAY := VARCHAR_ARRAY();
C NUMBER;
BEGIN
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('START: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
SELECT COUNT(COLUMN1)
INTO C
FROM MY_OTHER_TABLE
WHERE COLUMN1 IN (
-- Nested table replaced by a subquery
SELECT COLUMN1
FROM MY_TABLE
WHERE COLUMN1 = COL1
);
-- Print timestamp
DBMS_OUTPUT.PUT_LINE('ENDED: ' || TO_CHAR(SYSTIMESTAMP ,'dd-mm-yyyy hh24:mi:ss.FF'));
END;
The output is:
START: 01-08-2014 12:36:08.889
ENDED: 01-08-2014 12:36:08.903
It takes only 14 milliseconds...!!!
What could I do to enhance this PL-SQL block ?
Is there any database configuration needed?
Are the two query plans different?
Assuming that they are, the difference is likely that the optimizer has reasonable estimates about the number of rows the subquery will return and, thus, is able to choose the most efficient plan. When your data is in a nested table (I'd hate to use the word array in the type declaration here since that implies that you're using a varray when you're not), Oracle doesn't have information about how many elements are going to be in the collection. By default, it's going to guess that the collection has as many elements as your data blocks have bytes. So if you have 8k blocks, Oracle will guess that your collection has 8192 elements.
Assuming that your actual query doesn't return anywhere close to 8192 rows and that it actually returns many more or many fewer rows, you can potentially use the cardinality hint to let the optimizer make a more accurate guess. For example, if your query generally returns a few dozen rows, you probably want something like
SELECT COUNT(COLUMN1)
INTO C
FROM MY_OTHER_TABLE
WHERE COLUMN1 IN (SELECT /*+ cardinality(t 50) */ column_value
FROM TABLE(N_TBL) t);
The literal you put in the cardinality hint doesn't need to be particularly accurate, just close to general reality. If the number of rows is completely unknown the dynamic_sampling hint can help.
If you are using Oracle 11g, you may also benefit from cardinality feedback helping the optimizer learn to better estimate the number of elements in a collection.
I'm sure this is something simple, but I'm really new to PL/SQL and this has me stuck.
I've written a simple stored procedure to return a few values about a customer. Right off the bat, the %rowtype's are not coming up as reserved keywords but the compiler isn't flagging those as errors.
It is, however, ignoring the entire SQL statement flagging the line FROM demo_customers as too many values. Even if I try reducing it to only select one column it still gives me the same error.
create or replace
PROCEDURE GETCUSTOMER
(
arg_customerID demo_customers.customer_id%type,
returnRec OUT demo_customers%rowtype
)
AS
BEGIN
SELECT customer_id, cust_first_name, cust_last_name, cust_email
INTO returnRec
FROM demo_customers
WHERE customer_id = arg_customerID ;
END GETCUSTOMER;
If you want to select into a %ROWTYPE record, you'll want to do a SELECT * rather than selecting individual columns
create or replace
PROCEDURE GETCUSTOMER
(
arg_customerID demo_customers.customer_id%type,
returnRec OUT demo_customers%rowtype
)
AS
BEGIN
SELECT *
INTO returnRec
FROM demo_customers
WHERE customer_id = arg_customerID ;
END GETCUSTOMER;
If you select 4 columns explicitly, Oracle expects you to have 4 variables to select those values into.