I'm using informix IDS server, and I have this table table1 :
Column name Type Nulls
ad_code char(5) yes
ad_value smallint yes
I would like to generate a random, unique code for field ad_code (and then store it in the ad_code field) of table table1 using sql.
Is it possible ?
It would be enough, alternatively, an alphanumeric code sequnziale, es. 00001 ... 00009 ... 0000A unique
I have tried something like this, in the case of hexadecimal values in the
field ad_code:
select first 5 ('0x'||NVL( l.ad_code, '0'))::INT + 1
from table1 as l
left outer join table1 as r on
('0x'||NVL( l.ad_code, '0'))::INT + 1 =
('0x'||NVL( r.ad_code, '0'))::INT
where
r.ad_code is null ORDER BY 1 ASC;
commit;
but is very slow despite having created an index on ad_code.
You can generate 15-bit random numbers using this pair of stored procedures:
-- #(#)$Id: random.spl,v 1.2 1997/12/08 19:31:44 johnl Exp $
--
-- Simple emulation of SRAND and RAND in SPL
-- Using random number generator suggested by C standard (ISO 9899:1990)
CREATE PROCEDURE sp_setseed(n INTEGER)
DEFINE GLOBAL seed DECIMAL(10) DEFAULT 1;
LET seed = n;
END PROCEDURE;
CREATE PROCEDURE sp_random() RETURNING INTEGER;
DEFINE GLOBAL seed DECIMAL(10) DEFAULT 1;
DEFINE d DECIMAL(20,0);
LET d = (seed * 1103515245) + 12345;
-- MOD function does not handle 20-digit values... Dammit!!
LET seed = d - 4294967296 * TRUNC(d / 4294967296);
RETURN MOD(TRUNC(seed / 65536), 32768);
END PROCEDURE;
You can use those numbers to generate a sequence of alphanumeric characters, with more or less finesse. A simple approach uses the random number modulo the number of alphanumeric characters (do you want [A-Z0-9] or [a-z0-9] or [A-Za-z0-9], or something else), and select a character each time. There is potential for unequal distributions if you are not careful (because if there are 32768 possible random numbers, and you have 36 possible characters, 8 of characters will have a 911 out of 32768 chance of being selected, while the other 28 will only have a 910 out of 32768 chance of being selected (and the problem is bigger if you use 62 characters — lower-case, upper-case and digits). There are ways to deal with that if it is a problem.
Here's the simple-minded, slightly skewed approach at work:
-- #(#)$Id: randomstring.spl,v 1.1 2018/08/27 16:43:59 jonathanleffler Exp $
--
-- Generate a random sequence of characters from given list
CREATE FUNCTION sp_randomstring(str VARCHAR(255), num INTEGER)
RETURNING VARCHAR(255) AS random_string;
DEFINE r VARCHAR(255);
DEFINE i INTEGER;
DEFINE n INTEGER;
DEFINE j INTEGER;
LET r = "";
LET n = LENGTH(str);
FOR i = 1 TO num
LET j = MOD(sp_random(), n) + 1;
LET r = r || SUBSTR(str, j, 1);
END FOR;
RETURN r;
END FUNCTION;
EXECUTE FUNCTION sp_randomstring("ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789", 20);
EXECUTE FUNCTION sp_randomstring("abcdefghijklmnopqrstuvwxyz0123456789", 21);
EXECUTE FUNCTION sp_randomstring("ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789", 22);
EXECUTE FUNCTION sp_randomstring("abcdefghijklmnopqrstuvwxyz0123456789", 23);
EXECUTE FUNCTION sp_randomstring("ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789", 24);
EXECUTE FUNCTION sp_randomstring("abcdefghijklmnopqrstuvwxyz0123456789", 24);
EXECUTE FUNCTION sp_randomstring("ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789", 23);
EXECUTE FUNCTION sp_randomstring("abcdefghijklmnopqrstuvwxyz0123456789", 22);
EXECUTE FUNCTION sp_randomstring("ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789", 21);
EXECUTE FUNCTION sp_randomstring("abcdefghijklmnopqrstuvwxyz0123456789", 20);
Sample output:
087TTLGDMSNXMAFL7PJG
cklp14dfk66308lxkzjyu
6JDTOJLC47UE9GWSHRBH55
gwpmrfwwwcykgqbn494bmeh
TNY3U3VMHN01UZS1GV4LOF0K
tm38v8qwqj6o0vrsh9gbb0w6
YF6QP6NT3VK5ARTFDL1N32B
vrb9pvww5cw6egsz9tniex
9OIY799Z694DBENBDFSFE
1gkj5adm3bswlo26wd5i
I didn't set the seed, so that code generates the same sequence every time. You might use a sequence to generate a new seed each time, or you might do something else to seed the generator. The seed is private to each session.
Related
Tables(columns) that are important here (there are more in my actual DB but I simplified):
Patients(PatientID, PatientNumber, DOB, Weight, RandomCode)
RandomNumbers(RandomNumberID, Available)
Sites(SiteID, SiteNumber)
Patients does not contain any data and is to be populated via a 3rd party GUI. RandomNumbers contains 50 entries. When a patient's data is first added to Patients, a random number 1-50 is selected, which is tied to RandomNumberID. The "available" column in RandomNumbers is treated as a boolean (T meaning available, F meaning unavailable). After the RandomNumberID is tied to a patient, that RandomNumberID cannot be used again (Available is switched to "F"). If an already used RandomNumber is assigned to a patient upon data entry, another randomly selected RandomNumberID is selected until one is found where Available is T.
Here is the storedproc that I've written so far:
GO
CREATE PROCEDURE uspPatientEntry
#intPatientID AS INTEGER OUTPUT
,#intPatientNumber AS INTEGER
,#intSiteID AS INTEGER
,#intRandomCode AS INTEGER
AS
SET NOCOUNT ON
SET XACT_ABORT ON
BEGIN TRANSACTION
SELECT #intPatientID = MAX (intPatientID) + 1
FROM TPatients TP (TABLOCKX)
SELECT #intPatientID = COALESCE(#intPatientID, 1)
SELECT #intPatientNumber = CONCAT(#intSiteID, #intPatientID)
INSERT INTO TPatients (intPatientID, intPatientNumber, intSiteID, intRandomCodeID)
VALUES (#intPatientID, #intPatientNumber, #intSiteID, #intRandomCode)
COMMIT TRANSACTION
GO
And here is another function I wrote to test it out:
DECLARE #intPatientID AS INTEGER = 0;
DECLARE #intSiteNumber AS INTEGER = 0;
DECLARE #intPatientNumber AS INTEGER = CONCAT(#intSiteNumber, #intPatientID);
DECLARE #intRandomCode AS INTEGER = FLOOR(RAND()*50)+1; -- This just picks a random integer 1-40. <- this is the heart of my question
EXECUTE uspPatientEntry #intPatientID OUTPUT, #intPatientNumber, 2, #intRandomCode
Would something like this work? Ignore syntax, just the general idea:
DECLARE #intRandomCode AS INTEGER;
SELECT #intRandomCode = FLOOR(RAND()*50+1;
FROM TRandomCodes TRC
WHERE TRC.blnAvailable = "T"
UPDATE TRandomCodes TRC
SET TRC.blnAvailable = "F"
WHERE #intRandomCode = TRC.intRandomNumberID;
Thank you
We have kiosks for customers to check their purchase volume for two different categories of items. They will input their mobile number, which will send an OTP to their mobile numbers and they will input it back to authenticate, the system has to check the data and display for them. As a developer, the kiosk supplier has provided us with a limited functionality development kit by which we can execute select statement on the database and display the returned values on the kiosk.
I have created an object type as follows:
CREATE OR REPLACE TYPE rebate_values
AS
OBJECT (ASales_total number,
ACurrent_Rebate_Percent number,
ANeeded_Sales number,
ANext_Rebate_Percent number,
BSales_total number,
BCurrent_Rebate_Percent number,
BNeeded_Sales number,
BNext_Rebate_Percent number);
A function to which I will pass customers' mobile to get their sales and rebate information:
CREATE OR REPLACE FUNCTION AA_rebate_function (P_phone IN NUMBER)
RETURN rebate_values
IS
A_P_Sales_total NUMBER;
A_P_Current_Rebate_Percent NUMBER;
A_P_Needed_Sales NUMBER;
A_P_Next_Rebate_Percent NUMBER;
B_P_Sales_total NUMBER;
B_P_Current_Rebate_Percent NUMBER;
B_P_Needed_Sales NUMBER;
B_P_Next_Rebate_Percent NUMBER;
P_CODE VARCHAR (10);
BEGIN
SELECT CC_CODE
INTO P_CODE
FROM CUSTOMERS
WHERE C_MOBILE = P_phone;
FOR OUTDATA
IN (
--My Query to retrieve the data
Select ................
)
LOOP
IF OUTDATA.CLASS = 'X'
THEN
A_P_Sales_total := OUTDATA.SALES_TOTAL;
A_P_Current_Rebate_Percent := OUTDATA.CURRENT_REBATE_PERCENT;
A_P_Needed_Sales := OUTDATA.NEEDED_SALES_FOR_HIGHER_REBATE;
A_P_Next_Rebate_Percent := OUTDATA.NEXT_HIGHER_REBATE_PERCENT;
END IF;
IF OUTDATA.CLASS = 'Y'
THEN
B_P_Sales_total := OUTDATA.SALES_TOTAL;
B_P_Current_Rebate_Percent := OUTDATA.CURRENT_REBATE_PERCENT;
B_P_Needed_Sales := OUTDATA.NEEDED_SALES_FOR_HIGHER_REBATE;
B_P_Next_Rebate_Percent := OUTDATA.NEXT_HIGHER_REBATE_PERCENT;
END IF;
END LOOP;
RETURN rebate_values (A_P_Sales_total,
A_P_Current_Rebate_Percent,
A_P_Needed_Sales,
A_P_Next_Rebate_Percent,
B_P_Sales_total,
B_P_Current_Rebate_Percent,
B_P_Needed_Sales,
B_P_Next_Rebate_Percent);
END;
/
The query takes 27 seconds to retrieve the values for each customer. Each customer will have 2 rows, so that's why I have used LOOP to collect the values.
When I execute the function:
SELECT AA_rebate_function (XXXXXXXXXX) FROM DUAL;
I get data as follows in a single column within 27 seconds:
(XXXX, X, XXXX, X, XXXX, X, XXXX, X)
But when I execute the function to get the values in different columns, it takes 27 x 8 seconds = 216 seconds, i.e., approximately 3.6 minutes which is a big issue as the customer cannot wait for 3.6 minutes on the kiosk to view the data.
SELECT x.c.ASales_total,
x.c.ACurrent_Rebate_Percent,
x.c.ANeeded_Sales,
x.c.ANext_Rebate_Percent,
x.c.BSales_total,
x.c.BCurrent_Rebate_Percent,
x.c.BNeeded_Sales,
x.c.BNext_Rebate_Percent
FROM (SELECT AA_rebate_function (XXXXXXXXXX) c FROM DUAL) x;
I have tried using stored procedure with OUT values but it doesn't fit in my environment as I cannot program to execute stored procedures from the kiosk development toolkit because it only supports select statements, checked with the supplier and they don't have any plan to add that support in near future.
I tried converting the single field into multiple columns using REGEXP_SUBSTR but I get a type conversion error as it is an array.
The query is very complex and has to calculate data for the last 10 years and has millions of rows, 27 seconds is actually the optimum time to get the desired results.
Interesting! I didn't realize that when you query a function that returns an object, it runs the function once for each column you reference the object in. That's awkward.
The easiest solution I could find for this is to switch your function to be PIPELINED. You'll need to create a nested table type to do this.
create type rebate_values_t is table of rebate_values;
/
CREATE OR REPLACE FUNCTION AA_rebate_function (P_phone IN NUMBER)
RETURN rebate_values_t PIPELINED
IS
... your code here ...
PIPE ROW (rebate_values (A_P_Sales_total,
A_P_Current_Rebate_Percent,
A_P_Needed_Sales,
A_P_Next_Rebate_Percent,
B_P_Sales_total,
B_P_Current_Rebate_Percent,
B_P_Needed_Sales,
B_P_Next_Rebate_Percent));
RETURN;
END;
/
SELECT x.ASales_total,
x.ACurrent_Rebate_Percent,
x.ANeeded_Sales,
x.ANext_Rebate_Percent,
x.BSales_total,
x.BCurrent_Rebate_Percent,
x.BNeeded_Sales,
x.BNext_Rebate_Percent
FROM TABLE(AA_rebate_function (XXXXXXXXXX)) x;
For some reason, this should only execute the function once, and take 27 seconds.
I've seen a bunch of different solutions on StackOverflow that span many years and many Postgres versions, but with some of the newer features like gen_random_bytes I want to ask again to see if there is a simpler solution in newer versions.
Given IDs which contain a-zA-Z0-9, and vary in size depending on where they're used, like...
bTFTxFDPPq
tcgHAdW3BD
IIo11r9J0D
FUW5I8iCiS
uXolWvg49Co5EfCo
LOscuAZu37yV84Sa
YyrbwLTRDb01TmyE
HoQk3a6atGWRMCSA
HwHSZgGRStDMwnNXHk3FmLDEbWAHE1Q9
qgpDcrNSMg87ngwcXTaZ9iImoUmXhSAv
RVZjqdKvtoafLi1O5HlvlpJoKzGeKJYS
3Rls4DjWxJaLfIJyXIEpcjWuh51aHHtK
(Like the IDs that Stripe uses.)
How can you generate them randomly and safely (as far as reducing collisions and reducing predictability goes) with an easy way to specify different lengths for different use cases, in Postgres 9.6+?
I'm thinking that ideally the solution has a signature similar to:
generate_uid(size integer) returns text
Where size is customizable depending on your own tradeoffs for lowering the chance of collisions vs. reducing the string size for usability.
From what I can tell, it must use gen_random_bytes() instead of random() for true randomness, to reduce the chance that they can be guessed.
Thanks!
I know there's gen_random_uuid() for UUIDs, but I don't want to use them in this case. I'm looking for something that gives me IDs similar to what Stripe (or others) use, that look like: "id": "ch_19iRv22eZvKYlo2CAxkjuHxZ" that are as short as possible while still containing only alphanumeric characters.
This requirement is also why encode(gen_random_bytes(), 'hex') isn't quite right for this case, since it reduces the character set and thus forces me to increase the length of the strings to avoid collisions.
I'm currently doing this in the application layer, but I'm looking to move it into the database layer to reduce interdependencies. Here's what the Node.js code for doing it in the application layer might look like:
var crypto = require('crypto');
var set = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
function generate(length) {
var bytes = crypto.randomBytes(length);
var chars = [];
for (var i = 0; i < bytes.length; i++) {
chars.push(set[bytes[i] % set.length]);
}
return chars.join('');
}
Figured this out, here's a function that does it:
CREATE OR REPLACE FUNCTION generate_uid(size INT) RETURNS TEXT AS $$
DECLARE
characters TEXT := 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
bytes BYTEA := gen_random_bytes(size);
l INT := length(characters);
i INT := 0;
output TEXT := '';
BEGIN
WHILE i < size LOOP
output := output || substr(characters, get_byte(bytes, i) % l + 1, 1);
i := i + 1;
END LOOP;
RETURN output;
END;
$$ LANGUAGE plpgsql VOLATILE;
And then to run it simply do:
generate_uid(10)
-- '3Rls4DjWxJ'
Warning
When doing this you need to be sure that the length of the IDs you are creating is sufficient to avoid collisions over time as the number of objects you've created grows, which can be counter-intuitive because of the Birthday Paradox. So you will likely want a length greater (or much greater) than 10 for any reasonably commonly created object, I just used 10 as a simple example.
Usage
With the function defined, you can use it in a table definition, like so:
CREATE TABLE users (
id TEXT PRIMARY KEY DEFAULT generate_uid(10),
name TEXT NOT NULL,
...
);
And then when inserting data, like so:
INSERT INTO users (name) VALUES ('ian');
INSERT INTO users (name) VALUES ('victor');
SELECT * FROM users;
It will automatically generate the id values:
id | name | ...
-----------+--------+-----
owmCAx552Q | ian |
ZIofD6l3X9 | victor |
Usage with a Prefix
Or maybe you want to add a prefix for convenience when looking at a single ID in the logs or in your debugger (similar to how Stripe does it), like so:
CREATE TABLE users (
id TEXT PRIMARY KEY DEFAULT ('user_' || generate_uid(10)),
name TEXT NOT NULL,
...
);
INSERT INTO users (name) VALUES ('ian');
INSERT INTO users (name) VALUES ('victor');
SELECT * FROM users;
id | name | ...
---------------+--------+-----
user_wABNZRD5Zk | ian |
user_ISzGcTVj8f | victor |
I'm looking for something that gives me "shortcodes" (similar to what Youtube uses for video IDs) that are as short as possible while still containing only alphanumeric characters.
This is a fundamentally different question from what you first asked. What you want here then is to put a serial type on the table, and to use hashids.org code for PostgreSQL.
This returns 1:1 with the unique number (serial)
Never repeats or has a chance of collision.
Also base62 [a-zA-Z0-9]
Code looks like this,
SELECT id, hash_encode(foo.id)
FROM foo; -- Result: jNl for 1001
SELECT hash_decode('jNl') -- returns 1001
This module also supports salts.
Review,
26 characters in [a-z]
26 characters in [A-Z]
10 characters in [0-9]
62 characters in [a-zA-Z0-9] (base62)
The function substring(string [from int] [for int]) looks useful.
So it looks something like this. First we demonstrate that we can take the random-range and pull from it.
SELECT substring(
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
1, -- 1 is 'a', 62 is '9'
1,
);
Now we need a range between 1 and 63
SELECT trunc(random()*62+1)::int+1
FROM generate_series(1,1e2) AS gs(x)
This gets us there.. Now we just have to join the two..
SELECT substring(
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
trunc(random()*62)::int+1
1
)
FROM generate_series(1,1e2) AS gs(x);
Then we wrap it in an ARRAY constructor (because this is fast)
SELECT ARRAY(
SELECT substring(
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
trunc(random()*62)::int+1,
1
)
FROM generate_series(1,1e2) AS gs(x)
);
And, we call array_to_string() to get a text.
SELECT array_to_string(
ARRAY(
SELECT substring(
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
trunc(random()*62)::int+1,
1
)
FROM generate_series(1,1e2) AS gs(x)
)
, ''
);
From here we can even turn it into a function..
CREATE FUNCTION random_string(randomLength int)
RETURNS text AS $$
SELECT array_to_string(
ARRAY(
SELECT substring(
'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789',
trunc(random()*62)::int+1,
1
)
FROM generate_series(1,randomLength) AS gs(x)
)
, ''
)
$$ LANGUAGE SQL
RETURNS NULL ON NULL INPUT
VOLATILE LEAKPROOF;
and then
SELECT * FROM random_string(10);
Thanks to Evan Carroll answer, I took a look on hashids.org.
For Postgres you have to compile the extension or run some TSQL functions.
But for my needs, I created something simpler based on hashids ideas (short, unguessable, unique, custom alphabet, avoid curse words).
Shuffle alphabet:
CREATE OR REPLACE FUNCTION consistent_shuffle(alphabet TEXT, salt TEXT) RETURNS TEXT AS $$
DECLARE
SALT_LENGTH INT := length(salt);
integer INT = 0;
temp TEXT = '';
j INT = 0;
v INT := 0;
p INT := 0;
i INT := length(alphabet) - 1;
output TEXT := alphabet;
BEGIN
IF salt IS NULL OR length(LTRIM(RTRIM(salt))) = 0 THEN
RETURN alphabet;
END IF;
WHILE i > 0 LOOP
v := v % SALT_LENGTH;
integer := ASCII(substr(salt, v + 1, 1));
p := p + integer;
j := (integer + v + p) % i;
temp := substr(output, j + 1, 1);
output := substr(output, 1, j) || substr(output, i + 1, 1) || substr(output, j + 2);
output := substr(output, 1, i) || temp || substr(output, i + 2);
i := i - 1;
v := v + 1;
END LOOP;
RETURN output;
END;
$$ LANGUAGE plpgsql VOLATILE;
The main function:
CREATE OR REPLACE FUNCTION generate_uid(id INT, min_length INT, salt TEXT) RETURNS TEXT AS $$
DECLARE
clean_alphabet TEXT := 'abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890';
curse_chars TEXT := 'csfhuit';
curse TEXT := curse_chars || UPPER(curse_chars);
alphabet TEXT := regexp_replace(clean_alphabet, '[' || curse || ']', '', 'gi');
shuffle_alphabet TEXT := consistent_shuffle(alphabet, salt);
char_length INT := length(alphabet);
output TEXT := '';
BEGIN
WHILE id != 0 LOOP
output := output || substr(shuffle_alphabet, (id % char_length) + 1, 1);
id := trunc(id / char_length);
END LOOP;
curse := consistent_shuffle(curse, output || salt);
output := RPAD(output, min_length, curse);
RETURN output;
END;
$$ LANGUAGE plpgsql VOLATILE;
How-to use examples:
-- 3: min-length
select generate_uid(123, 3, 'salt'); -- output: "0mH"
-- or as default value in a table
CREATE SEQUENCE IF NOT EXISTS my_id_serial START 1;
CREATE TABLE collections (
id TEXT PRIMARY KEY DEFAULT generate_uid(CAST (nextval('my_id_serial') AS INTEGER), 3, 'salt')
);
insert into collections DEFAULT VALUES ;
This query generate required string. Just change second parasmeter of generate_series to choose length of random string.
SELECT
string_agg(c, '')
FROM (
SELECT
chr(r + CASE WHEN r > 25 + 9 THEN 97 - 26 - 9 WHEN r > 9 THEN 64 - 9 ELSE 48 END) AS c
FROM (
SELECT
i,
(random() * 60)::int AS r
FROM
generate_series(0, 62) AS i
) AS a
ORDER BY i
) AS A;
So I had my own use-case for something like this. I am not proposing a solution to the top question, but if you are looking for something similar like I am, then try this out.
My use-case was that I needed to create a random external UUID (as a primary key) with as few characters as possible. Thankfully, the scenario did not have a requirement that a large amount of these would ever be needed (probably in the thousands only). Therefore a simple solution was a combination of using generate_uid() and checking to make sure that the next sequence was not already used.
Here is how I put it together:
CREATE OR REPLACE FUNCTION generate_id (
in length INT
, in for_table text
, in for_column text
, OUT next_id TEXT
) AS
$$
DECLARE
id_is_used BOOLEAN;
loop_count INT := 0;
characters TEXT := 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789';
loop_length INT;
BEGIN
LOOP
next_id := '';
loop_length := 0;
WHILE loop_length < length LOOP
next_id := next_id || substr(characters, get_byte(gen_random_bytes(length), loop_length) % length(characters) + 1, 1);
loop_length := loop_length + 1;
END LOOP;
EXECUTE format('SELECT TRUE FROM %s WHERE %s = %s LIMIT 1', for_table, for_column, quote_literal(next_id)) into id_is_used;
EXIT WHEN id_is_used IS NULL;
loop_count := loop_count + 1;
IF loop_count > 100 THEN
RAISE EXCEPTION 'Too many loops. Might be reaching the practical limit for the given length.';
END IF;
END LOOP;
END
$$
LANGUAGE plpgsql
STABLE
;
here is an example table usage:
create table some_table (
id
TEXT
DEFAULT generate_id(6, 'some_table', 'id')
PRIMARY KEY
)
;
and a test to see how it breaks:
DO
$$
DECLARE
loop_count INT := 0;
BEGIN
-- WHILE LOOP
WHILE loop_count < 1000000
LOOP
INSERT INTO some_table VALUES (DEFAULT);
loop_count := loop_count + 1;
END LOOP;
END
$$ LANGUAGE plpgsql
;
In DB2 9.7 I am looking for a way to reverse a string in a SQL query.
I am familiar with SQL Server where the query would be like
SELECT
REVERSE(LEFT_TO_REIGHT) AS RIGHT_TO_LEFT
FROM
TABLE1;
I couldn't find a similar function in DB2. is there a simple way to reverse a string?
Creating a REVERSE(..) function is unnecessary.
DB2 has something called RIGHT(string-expression, length):
The RIGHT function returns the rightmost string of string-expression
of length length, expressed in the specified string unit. If
string-expression is a character string, the result is a character
string. If string-expression is a graphic string, the result is a
graphic string
So if you're interested in the last 8 characters, you can pretty trivially do this via:
SELECT RIGHT(left_to_right, 8) AS right_to_left
FROM Table1
(I'm actually still concerned about the fact that you're splitting off 8 characters consistently, as it implies you have a multi-part key of some sort).
Try something like:
SELECT STRIP(CAST( TRANSLATE('87654321',LEFT_TO_REIGHT, '12345678') AS VARCHAR(8) ))
FROM TABLE1;
Due to the original question this is the first webpage that comes up when one searches for 'How to reverse a string in DB2'.
Here is an answer that doesn't require implementing it in C and shouldn't brake on non-pure-Engilsh strings regardless of their length.
Be warned though, the efficiency is 'meh' at best.
CREATE FUNCTION REVERSE_STRING(STR VARCHAR(100))
RETURNS VARCHAR(100)
LANGUAGE SQL
SPECIFIC REVERSE_STRING
DETERMINISTIC
REVERSE: BEGIN
DECLARE REVERSED_STRING VARCHAR(100);
DECLARE REVERSED_CHARACTERS_INDEX INTEGER;
SET REVERSED_STRING='';
SET REVERSED_CHARACTERS_INDEX=0;
WHILE (REVERSED_CHARACTERS_INDEX < CHARACTER_LENGTH(STR, CODEUNITS16))
DO
SET REVERSED_CHARACTERS_INDEX = REVERSED_CHARACTERS_INDEX + 1;
SET REVERSED_STRING = CONCAT(
REVERSED_STRING,
LEFT(RIGHT(STR, REVERSED_CHARACTERS_INDEX, CODEUNITS16), 1, CODEUNITS16));
END WHILE;
RETURN REVERSED_STRING;
END REVERSE#
The idea is to get a substring which starts from the n-th character from the right till the end of the string, then take the first element of this substring from the left and append it to a reversed string. This operation is conducted n times where n is the length of a string to be reversed.
You can use it like any other function.
SELECT FIRSTNME AS FIRSTNAME, REVERSE_STRING(FIRSTNME) AS REVERSED_FIRSTNAME
FROM SAMPLE.EMPLOYEE#
Example output
Answering the original question of reversing a string there's user defined functions published on the IBM site that will do it that you can find here. There's apparently no built in ability in DB2
https://www.ibm.com/developerworks/community/blogs/SQLTips4DB2LUW/entry/reverse?lang=en
Tortured SQL version:
CREATE OR REPLACE FUNCTION REVERSE(INSTR VARCHAR(4000))
RETURNS VARCHAR(4000) SPECIFIC REVERSE
DETERMINISTIC NO EXTERNAL ACTION CONTAINS SQL
RETURN WITH rec(pos, res) AS (VALUES (1, CAST('' AS VARCHAR(4000)))
UNION ALL
SELECT pos + 1, SUBSTR(INSTR, pos , 1) || res
FROM rec
WHERE pos <= LENGTH(INSTR)
AND pos < 5000)
SELECT res FROM rec WHERE pos > LENGTH(INSTR);
But then you have to do this as well, yuck:
CREATE BUFFERPOOL bp32 PAGESIZE 32K;
CREATE SYSTEM TEMPORARY TABLESPACE tsp32 PAGESIZE 32K BUFFERPOOL bp32;
A saner C implementation
#include <sqludf.h>
#ifdef __cplusplus
extern "C"
#endif
void SQL_API_FN ReverseSBCP(SQLUDF_VARCHAR *inVarchar,
SQLUDF_VARCHAR *outVarchar,
SQLUDF_SMALLINT *inVarcharNullInd,
SQLUDF_SMALLINT *outVarcharNullInd,
SQLUDF_TRAIL_ARGS)
{
int inLen, inPos, outPos;
if (*inVarcharNullInd == -1)
{
*outVarcharNullInd = -1;
}
else
{
inLen = strlen(inVarchar);
for (inPos = 0, outPos = inLen -1; inPos < inLen; inPos++, outPos--)
{
outVarchar[outPos] = inVarchar[inPos];
}
outVarchar[inLen] = '\0';
*outVarcharNullInd = 0;
}
return;
}
I have below code. I am using Oracle 11g.
SELECT DBMS_OBFUSCATION_TOOLKIT.md5 (input => UTL_RAW.cast_to_raw(
FIRST_NAME
||LAST_NAME
)) md5_key ,
FIRST_NAME ,
LAST_NAME
FROM C_NAME_TAB
WHERE PKEY='1234'
How can i call this code? Can i directly execute this code in sqldeveloper?
In Oracle 12c you can use the function STANDARD_HASH. It does not require any additional privileges.
select standard_hash('foo', 'MD5') from dual;
The dbms_obfuscation_toolkit is deprecated (see Note here). You can use DBMS_CRYPTO directly:
select rawtohex(
DBMS_CRYPTO.Hash (
UTL_I18N.STRING_TO_RAW ('foo', 'AL32UTF8'),
2)
) from dual;
Output:
ACBD18DB4CC2F85CEDEF654FCCC4A4D8
Add a lower function call if needed. More on DBMS_CRYPTO.
I would do:
select DBMS_CRYPTO.HASH(rawtohex('foo') ,2) from dual;
output:
DBMS_CRYPTO.HASH(RAWTOHEX('FOO'),2)
--------------------------------------------------------------------------------
ACBD18DB4CC2F85CEDEF654FCCC4A4D8
#user755806 I do not believe that your question was answered. I took your code but used the 'foo' example string, added a lower function and also found the length of the hash returned. In sqlplus or Oracle's sql developer Java database client you can use this to call the md5sum of a value. The column formats clean up the presentation.
column hash_key format a34;
column hash_key_len format 999999;
select dbms_obfuscation_toolkit.md5(
input => UTL_RAW.cast_to_raw('foo')) as hash_key,
length(dbms_obfuscation_toolkit.md5(
input => UTL_RAW.cast_to_raw('foo'))) as hash_key_len
from dual;
The result set
HASH_KEY HASH_KEY_LEN
---------------------------------- ------------
acbd18db4cc2f85cedef654fccc4a4d8 32
is the same value that is returned from a Linux md5sum command.
echo -n foo | md5sum
acbd18db4cc2f85cedef654fccc4a4d8 -
Yes you can call or execute the sql statement directly in sqlplus or sql developer. I tested the sql statement in both clients against 11g.
You can use any C, C#, Java or other programming language that can send a statement to the database. It is the database on the other end of the call that needs to be able to understand the sql statement. In the case of 11 g, the code will work.
#tbone provides an excellent warning about the deprecation of the dbms_obfuscation_toolkit. However, that does not mean your code is unusable in 12c. It will work but you will want to eventually switch to dbms_crypto package. dbms_crypto is not available in my version of 11g.
To calculate MD5 hash of CLOB content field with my desired encoding without implicitly recoding content to AL32UTF8, I've used this code:
create or replace function clob2blob(AClob CLOB) return BLOB is
Result BLOB;
o1 integer;
o2 integer;
c integer;
w integer;
begin
o1 := 1;
o2 := 1;
c := 0;
w := 0;
DBMS_LOB.CreateTemporary(Result, true);
DBMS_LOB.ConvertToBlob(Result, AClob, length(AClob), o1, o2, 0, c, w);
return(Result);
end clob2blob;
/
update my_table t set t.hash = (rawtohex(DBMS_CRYPTO.Hash(clob2blob(t.content),2)));