I want to convert game tag data found here into a dimension table of a star schema.
But the problem is that steamspy_tag_data table is organised as such every column name is tag name of a game and one game can have multiple tags. For example, lets say I have game Warcraft3 with appid 30 it would be in a table like this.
appid|strategy|action|shooter|fantasy|
-----+--------+------+-------+-------
30 6345 1452 0 6340
Column value greater than 0 signifies amount of user votes that voted certain game to be of that game tag. For Warcraft3 game with appid 30 - 6345 users voted it classifies as strategy 1452 users it classifies as action, .. etc.
Some columns for example "abstract" (column) tag has almost all 0 throughout the whole column meaning almost no game uses that tag, so to simplify 372 columns with over 29k row value into something more compact I want to run a query that would count non-zero value per every tag column and put them in the new table "tagovi" for better visibility which columns(tags) have relatively low game usage count.
so far I came up with this:
CREATE DEFINER=`root`#`localhost` PROCEDURE `zbroji_tagove`()
BEGIN
DECLARE i INTEGER;
DECLARE total_row_count INTEGER;
DECLARE dummy VARCHAR(255);
DECLARE zbrojeno INTEGER;
DECLARE trenutna VARCHAR(255);
DECLARE kursor CURSOR FOR
SELECT column_name
FROM INFORMATION_SCHEMA.COLUMNS
WHERE table_schema = 'sppi' AND table_name = 'steamspy_tag_data'
ORDER BY ordinal_position;
SELECT FOUND_ROWS() into total_row_count;
open kursor;
FETCH kursor into dummy;
SET i = 1;
ponavljanje: LOOP
IF i > total_row_count THEN
CLOSE kursor;
LEAVE ponavljanje;
END IF;
FETCH kursor INTO trenutna;
SET zbrojeno = 0;
SET zbrojeno = (SELECT COUNT(*) FROM steamspy_tag_data where trenutna <> 0);
INSERT INTO tagovi(kategorija,broj_igra)
VALUES (
(trenutna),(zbrojeno)
);
SET i = i + 1;
end LOOP;
END
New table tagovi has 3 columns (ID auto_increment, kategorija Varchar(255), broj_igra INTEGER).
When I execute my stored procedure "zbroji_tagove"() I get SQL ERROR CODE 1292; Truncated incorrect DOUBLE value 'some_tag_name'. So somehow sql treats variable value as value instead of column at line SET zbrojeno = (SELECT COUNT() FROM steamspy_tag_data where trenutna <> 0*);
Is there a way for me to accomplish what I want inside MySQL environment?
You can't use variables like that, you need a prepared statement
See
#sql = CONCAT("SELECT COUNT(*) INTO zbrojeno FROM steamspy_tag_data where ",trenutna," <> 0);";
PREPARE stmt1 FROM #sql;
EXECUTE stmt1;
DEALLOCATE PREPARE stmt1;
I have been trying to create a simple loop of SELECT statements in MySQL to reduce code. I have started this using CONCAT() however this causes the procedure to stop/fail. For example (where k is a loop counter):
CONCAT('SELECT (Child_', k, ' INTO #Age_Child_', k, ' FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1)');
To diagnose the issue, I simply tried to place the SELECT statement (without concatenated loop variables) inside a string to then be executed. While I could get this to work for simple statements it would not work for the following:
SET #queryString = CONCAT('SELECT Child_1 INTO #Age_Child_1 FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1');
PREPARE stmt FROM #queryString;
EXECUTE stmt;
Does anyone know why the #queryString containing the CONCAT() statement will not be executed/cause the procedure to fail?
tl;dr The statement you're trying to write has the form SELECT(rest of statement) LIMIT 1. It should have the form SELECT rest of statement LIMIT 1.
It looks like you want to create variable column names, ummm, because your lookup_childage table is denormalized. I guess that table has these columns.
Child_1 INT
Child_2 INT
Child_3 INT
Child_4 INT
It looks like you hope to get a #queryString value containing this sort of thing:
SELECT Child_4 INTO #Age_Child_4 FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1
Only the 4s are variable.
So to get that string you want
SELECT CONCAT('SELECT Child_', k,
' INTO #Age_Child_', k,
' FROM lookup_childage WHERE ModYear = ModYear_var LIMIT 1'
)
INTO #queryString;
I'm totally new with stored procedure and I'm trying to understand its basic concepts. This is my first one and of course there is something wrong.
Basically the query is going to be the same (the original is more complex and there are other operations) but the WHERE clause changes according to the selType param. So what I'm trying to do is a sort of "variabilisation" of the WHERE clause according to the param value.
I don't know whether this is the correct approach and, if yes, what's wrong with it.
DELIMITER //
CREATE PROCEDURE `testProcedure` (IN addressId INT, IN selType BOOLEAN)
BEGIN
DECLARE whereUserCriteria VARCHAR(127);
IF selType = 1 THEN
SET whereUserCriteria = CONCAT('address_id = ', addressId);
ELSE
SET whereUserCriteria = 'address_id = 1';
END IF;
SELECT whatever
FROM wherever AS ad
WHERE whereUserCriteria ;
END //
It's nice to see that when it's not variabilised, it works perfectly but, as soon as i use a variable to make it dynamic, it stops working.
Of course this is a mere example aimed to understand what's the best approach in cases like this.
You can prepare query concatenating the queries and condition together and execute that using Prepared Execute statement as follows(as mentioned in the comment above):
DELIMITER //
CREATE PROCEDURE `testProcedure` (IN addressId INT, IN selType BOOLEAN)
BEGIN
DECLARE whereUserCriteria VARCHAR(127);
IF selType = 1 THEN
SET whereUserCriteria = CONCAT('address_id = ', addressId);
ELSE
SET whereUserCriteria = 'address_id = 1';
END IF;
SET #myQuery = '';
SET #myQuery = CONCAT("SELECT whatever FROM wherever AS ad
WHERE ",whereUserCriteria,") ;
PREPARE stmQuery FROM #myQuery;
EXECUTE stmQuery;
DEALLOCATE PREPARE stmQuery;
END //
DELIMITER ;
You probably want do dynamic query.
But you can rewrite your sample using CASE like this (but not sure if that is what you want):
SELECT whatever
FROM wherever AS ad
WHERE address_id = CASE WHEN selType = 1
THEN addressId
ELSE 1
END;
I'm quite new to subject of writting stored function for mySQL database, hence i'm not sure if what i'm trying to do here is possible at all.
I need a function that will return a column from random row from a table. I don't want to use ORDER BY RAND() method to do that, rather i would do this like this:
DECLARE MAX_COUNT INT DEFAULT 120000;
DECLARE rand_offset INT;
DECLARE str_rnd_word VARCHAR(255);
SET rand_offset = FLOOR((RAND() * MAX_COUNT));
SELECT word INTO str_rnd_word FROM all_words LIMIT 1 OFFSET rand_offset ;
RETURN str_rnd_word;
MySQL throws an error upon creating function with body like that. But when I use hard-coded number as OFFSET it works just fine.
Can someone shed some light on the subject please.
I'm running MySQL 5.0.45 on windows box.
Thanks
In MySQL before 5.5, you can't put a variable into the LIMIT clause in MySQL stored procedures. You have to interpolate it into a string and then execute the string as a dynamic query.
SET rand_offset = FLOOR(RAND() * (SELECT COUNT(*) FROM all_words));
SET #sql = CONCAT('SELECT word INTO str_rnd_word FROM all_words LIMIT 1 OFFSET ', rand_offset);
PREPARE stmt1 FROM #sql;
EXECUTE stmt1;
I am writing a stored procedure where I have an input parameter called my_size that is an INTEGER. I want to be able to use it in a LIMIT clause in a SELECT statement. Apparently this is not supported, is there a way to work around this?
# I want something like:
SELECT * FROM some_table LIMIT my_size;
# Instead of hardcoding a permanent limit:
SELECT * FROM some_table LIMIT 100;
For those, who cannot use MySQL 5.5.6+ and don't want to write a stored procedure, there is another variant. We can add where clause on a subselect with ROWNUM.
SET #limit = 10;
SELECT * FROM (
SELECT instances.*,
#rownum := #rownum + 1 AS rank
FROM instances,
(SELECT #rownum := 0) r
) d WHERE rank < #limit;
STORED PROCEDURE
DELIMITER $
CREATE PROCEDURE get_users(page_from INT, page_size INT)
BEGIN
SET #_page_from = page_from;
SET #_page_size = page_size;
PREPARE stmt FROM "select u.user_id, u.firstname, u.lastname from users u limit ?, ?;";
EXECUTE stmt USING #_page_from, #_page_size;
DEALLOCATE PREPARE stmt;
END$
DELIMITER ;
USAGE
In the following example it retrieves 10 records each time by providing start as 1 and 11. 1 and 11 could be your page number received as GET/POST parameter from pagination.
call get_users(1, 10);
call get_users(11, 10);
A search turned up this article. I've pasted the relevant text below.
Here's a forum post showing an example of prepared statements letting
you assign a variable value to the limit clause:
http://forums.mysql.com/read.php?98,126379,133966#msg-133966
However, I think this bug should get some attention because I can't
imagine that prepared statements within a procedure will allow for any
procedure-compile-time optimizations. I have a feeling that prepared
statements are compiled and executed at the runtime of the procedure,
which probaby has a negative impact on efficiency. If the limit
clause could accept normal procedure variables (say, a procedure
argument), then the database could still perform compile-time
optimizations on the rest of the query, within the procedure. This
would likely yield faster execution of the procedure. I'm no expert
though.
I know this answer has come late, but try SQL_SELECT_LIMIT.
Example:
Declare rowCount int;
Set rowCount = 100;
Set SQL_SELECT_LIMIT = rowCount;
Select blah blah
Set SQL_SELECT_LIMIT = Default;
This feature has been added to MySQL 5.5.6.
Check this link out.
I've upgraded to MySQL 5.5 just for this feature and works great.
5.5 also has a lot of performance upgrades in place and I totally recommend it.
Another way, the same as wrote "Pradeep Sanjaya", but using CONCAT:
CREATE PROCEDURE `some_func`(startIndex INT, countNum INT)
READS SQL DATA
COMMENT 'example'
BEGIN
SET #asd = CONCAT('SELECT `id` FROM `table` LIMIT ',startIndex,',',countNum);
PREPARE zxc FROM #asd;
EXECUTE zxc;
END;
As of MySQL version 5.5.6, you can specify LIMIT and OFFSET with variables / parameters.
For reference, see the 5.5 Manual, the 5.6 Manual and #Quassnoi's answer
I've faced the same problem using MySql 5.0 and wrote a procedure with the help of #ENargit's answer:
CREATE PROCEDURE SOME_PROCEDURE_NAME(IN _length INT, IN _start INT)
BEGIN
SET _start = (SELECT COALESCE(_start, 0));
SET _length = (SELECT COALESCE(_length, 999999)); -- USING ~0 GIVES OUT OF RANGE ERROR
SET #row_num_personalized_variable = 0;
SELECT
*,
#row_num_personalized_variable AS records_total
FROM(
SELECT
*,
(#row_num_personalized_variable := #row_num_personalized_variable + 1) AS row_num
FROM some_table
) tb
WHERE row_num > _start AND row_num <= (_start + _length);
END;
Also included the total rows obtained by the query with records_total.
you must DECLARE a variable and after that set it. then the LIMIt will work and put it in a StoredProcedure not sure if it works in normal query
like this:
DECLARE rowsNr INT DEFAULT 0;
SET rowsNr = 15;
SELECT * FROM Table WHERE ... LIMIT rowsNr;