How to have this code/output in MySql:
Had a recursive cte in MSSQL to fill a table with random data without loop e.g begin/end. Searched for similar logic in MySql but most or all solutions were using begin/end or for loops. Wonder if you could suggest a solution without loop in MySql.
Thanks
--MSSQL cte:------------------------------------
with t1( idi,val ) as
(
select
idi=1
,val=cast( 1 as real)
union all
select
idi=idi+1
,val=cast(val+rand() as real)
from t1
where idi<5
)
select idi,val from t1
-----------------------------------------------
Output in MSSQL:( semi random values)
idi | val
-------------
1 | 1
2 | 1.11
3 | 1.23
4 | 1.35
5 | 1.46
Edit:
Regarding discussions which considers set based codes as loop based codes indeed, I could understand this but just out of interest gave it a try in MSSQL 2008r2, here is the result:
1- above code with 32000 recursion took 2.812 sec
2- above output created with WHILE BEGIN END loop for 32000 took 53.640 sec
Obviously this is a big difference in execution time.
Here is the loop based code:
insert into #t1(idi,val)
select
idi=1
,val=1
declare #ii int = 2
while #ii<32000
begin
insert into #t1(idi,val)
select
idi=idi+1
,val=val+rand()
from #t1
where idi=#ii-1
set #ii=#ii+1
end
select * from #t1
MySql doesn't support CTE.
You need a procedure or some tricky queries like this one:
set #id=0;
set #val=0;
SELECT #id:=#id+1 As id,
#val:=#val+rand() As val
FROM information_schema.tables x
CROSS JOIN information_schema.tables y
LIMIT 10
Related
I have created a stored function within phpmyadmin which calculates across several fields to derive an overall value. I'm using a function as the calculation needs to be used several times, across several scripts so to my knowledge, this is the most efficient way to do this to minimise code updates.
I've tested the function and it works in terms of providing an output, however when I combine it with my query, it provides an aggregated figure across the query results rather than a specific figure per row:
Function Code:
BEGIN
DECLARE Output_needed INT(7);
SET Output_needed = (select SUM(Col1+Col2+Col3) from table1);
RETURN (Output_needed);
END
SQL Query:
Select ID, function_name(), Col1, Col2, Col3 from table1
Required Query Output
ID Function Returns *Output_needed* Col1 Col2 Col3
1 100 *10* 4 4 2
2 100 *50* 10 20 20
3 100 *5* 1 2 2
4 100 *15* 10 2 3
5 100 *20* 6 3 1
Can someone advise where I am going wrong? I assume I've missed a step somewhere but cant seem to figure it out.
Thanks!
The function select query doesn't have the condition to get the single row result.So, I have just added the one field for conditional use.
Function:
DELIMITER $$
CREATE DEFINER=`root`#`localhost` FUNCTION `function_name`(pk_field INT) RETURNS int(11)
BEGIN
DECLARE output_needed INT;
SELECT SUM(Col1+Col2+Col3) INTO output_needed FROM table1 WHERE pk_field_name = pk_field;
RETURN output_needed;
END$$
DELIMITER ;
SELECT Query:
Select ID, function_name(pk_field_name), Col1, Col2, Col3 from table1
I am trying to automate the production of a roster based on leave dates and working preferences. I have generated some data to work with and I now have two tables - one with a list of individuals and their preferences for working on particular days of the week(e.g. some prefer to work on a Tuesday, others only every other Wednesday, etc), and another with leave dates for individuals. That looks like this, where firstpref and secondpref represent weekdays with Mon = 1, Sun = 7 and firstprefclw represents a marker for which week of a 2 week pattern someone prefers (0 = no pref, 1 = wk 1 preferred, 2 = wk2 preferred)
initials | firstpref | firstprefclw | secondpref | secondprefclw
KP | 3 | 0 | 1 | 0
BD | 2 | 1 | 1 | 0
LW | 3 | 0 | 4 | 1
Then there is a table leave_entries which basically has the initials, a start date, and an end date for each leave request.
Finally, there is a pre-calculated clwdates table which contains a marker (a 1 or 2) for each day in one of its columns as to what week of the roster pattern it is.
I have run this query:
SELECT #tdate, DATE_FORMAT(#tdate,'%W') AS whatDay, GROUP_CONCAT(t1.initials separator ',') AS available
FROM people AS t1
WHERE ((t1.firstpref = (DAYOFWEEK(#tdate))-1
AND (t1.firstprefclw = 0 OR (t1.firstprefclw = (SELECT c_dates.clw from clwdates AS c_dates LIMIT i,1))))
OR (t1.secondpref = (DAYOFWEEK(#tdate))-1
AND (t1.secondprefclw = 0 OR (t1.secondprefclw = (SELECT c_dates.clw from clwdates AS c_dates LIMIT i,1)))
OR ((DAYOFWEEK(#tdate))-1 IN (0,5,6))
AND t1.initials NOT IN (SELECT initials FROM leave_entries WHERE #tdate BETWEEN leave_entries.start_date and leave_entries.end_date)
);
My output from that is a list of dates with initials of the pattern:
2018-01-03;Wednesday;KP,LW,TH
My desired output is
2018-01-03;Wednesday;KP
Where the initials of the person have been randomly selected from the list of available people generated by the first set of SELECTs.
I have seen a SO post where a suggestion of how to do this has been made involving SUBSTRING_INDEX (How to select Random Sub string,which seperated by coma(",") From a string), however I note the comment that CSV is not the way to go, and since I have a table which is not CSV, I am wondering:
How can I randomly select an individual's initials from the available ones and create a table which is basically date ; random_person?
So I figured out how to do it.
The first select (outlined above) forms the heart of a PROCEDURE called ROWPERROW() and generates a table called available_people
This is probably filthy MySQL code, but it works:
SET #tdate = 0
DROP TABLE IF EXISTS on_call;
CREATE TABLE working(tdate DATE, whatDay VARCHAR(20), selected VARCHAR(255));
DELIMITER //
DROP PROCEDURE IF EXISTS ROWPERROW2;
CREATE PROCEDURE ROWPERROW2()
BEGIN
DECLARE n INT DEFAULT 0;
DECLARE kk INT DEFAULT 0;
SET n=90; -- or however many days the roster is going to run for
SET kk=0;
WHILE kk<n DO
SET #tdate = (SELECT c_dates.fulldate from clwdates AS c_dates LIMIT kk,1);
INSERT INTO working
SELECT #tdate, DATE_FORMAT(#tdate,'%W') AS whatDay, t1.available
FROM available_people AS t1 -- this is the table created by the first query above
WHERE tdate = #tdate ORDER BY RAND() LIMIT 1;
SET kk = kk + 1;
END WHILE;
end;
//
DELIMITER ;
CALL ROWPERROW2();
SELECT * from working;
Is there a function like "unnest" from POSTGRESQL on MYSQL?
Query (PSQL):
select unnest('{1,2,3,4}'::int[])
Result (as table):
int |
_____|
1 |
_____|
2 |
_____|
3 |
_____|
4 |
_____|
Short answer
Yes, it is possible. From technical viewpoint, you can achieve that with one query. But the thing is - most probably, you are trying to pass some logic from application to data storage. Data storage is intended to store data, not to represent/format it or, even more, apply some logic to it.
Yes, MySQL doesn't have arrays data type, but in most cases it won't be a problem and architecture can be created so it will fit those limitations. And in any case, even if you'll achieve it somehow (like - see below) - you won't be possible to properly work later with that data, since it will be just result set. You may store it, of course - so to, let's say, index later, but then it's again a task for an application - so to create that import.
Also, make sure that it is not a Jaywalker case, so not about storing delimiter-separated values and later trying to extract them.
Long answer
From technical viewpoint, you can do it with Cartesian product of the two row sets. Then use a well known formula:
N = d1x101 + d2x102 + ...
Thus, you'll be able to create a "all-numbers" table and later iterate through it. That iteration, together with MySQL string functions, may lead you to something like this:
SELECT
data
FROM (
SELECT
#next:=LOCATE(#separator,#search, #current+1) AS next,
SUBSTR(SUBSTR(#search, #current, #next-#current), #length+1) AS data,
#next:=IF(#next, #next, NULL) AS marker,
#current:=#next AS current
FROM
(SELECT 0 as i UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) as n1
CROSS JOIN
(SELECT 0 as i UNION ALL SELECT 1 UNION ALL SELECT 2 UNION ALL SELECT 3 UNION ALL SELECT 4 UNION ALL SELECT 5 UNION ALL SELECT 6 UNION ALL SELECT 7 UNION ALL SELECT 8 UNION ALL SELECT 9) as n2
CROSS JOIN
(SELECT
-- set your separator here:
#separator := ',',
-- set your string here:
#data := '1,25,42,71',
-- and do not touch here:
#current := 1,
#search := CONCAT(#separator, #data, #separator),
#length := CHAR_LENGTH(#separator)) AS init
) AS joins
WHERE
marker IS NOT NULL
The corresponding fiddle would be here.
You should also notice: this is not a function. And with functions (I mean, user-defined with CREATE FUNCTION statement) it's impossible to get result row set since function in MySQL can not return result set by definition. However, it's not true to say that it's completely impossible to perform requested transformation with MySQL.
But remember: if you are able to do something, that doesn't mean you should do it.
This sample fetchs all "catchwords" from Table data, wich are seperated by ","
Maximum values in the commaseparated list is 100
WITH RECURSIVE num (n) AS (
SELECT 1
UNION ALL
SELECT n+1 FROM num WHERE n<100 -- change this, if more than 100 elements
)
SELECT DISTINCT substring_index(substring_index(catchwords, ',', n), ',', -1) as value
FROM data
JOIN num
ON char_length(catchwords) - char_length(replace(catchwords, ',', '')) >= n - 1
In newer Version of MySQL/MariaDB you can use JSON_TABLE if you can JOIN the elements:
SELECT cat.catchword, dat.*
FROM data dat
CROSS JOIN json_table(concat('[',dat.catchwords, ']')
, '$[*]' COLUMNS(
catchword VARCHAR(50) PATH '$'
)
) AS words
when I DELETE, as example, the id 3, I have this:
id | name
1 |
2 |
4 |
5 |
...
now, I want to search for the missing id(s), because i want to fill the id again with:
INSERT INTO xx (id,...) VALUES (3,...)
is there a way to search for "holes" in the auto_increment index?
thanks!
You can find the top value of gaps like this:
select t1.id - 1 as missing_id
from mytable t1
left join mytable t2 on t2.id = t1.id - 1
where t2.id is null
The purpose of AUTO_INCREMENT is to generate simple unique and meaningless identifiers for your rows. As soon as you plan to re-use those IDs, they're no longer unique (not at least in time) so I have the impression that you are not using the right tool for the job. If you decide to get rid of AUTO_INCREMENT, you can do all your inserts with the same algorithm.
As about the SQL code, this query will match existing rows with the rows that has the next ID:
SELECT a.foo_id, b.foo_id
FROM foo a
LEFT JOIN foo b ON a.foo_id=b.foo_id-1
E.g.:
1 NULL
4 NULL
10 NULL
12 NULL
17 NULL
19 20
20 NULL
24 25
25 26
26 27
27 NULL
So it's easy to filter out rows and get the first gap:
SELECT MIN(a.foo_id)+1 AS next_id
FROM foo a
LEFT JOIN foo b ON a.foo_id=b.foo_id-1
WHERE b.foo_id IS NULL
Take this as a starting point because it still needs some tweaking:
You need to consider the case where the lowest available number is the lowest possible one.
You need to lock the table to handle concurrent inserts.
In my computer it's slow as hell with big tables.
I think the only way you can do this is with a loop:
Any other solutions wont show gaps bigger than 1:
insert into XX values (1)
insert into XX values (2)
insert into XX values (4)
insert into XX values (5)
insert into XX values (10)
declare #min int
declare #max int
select #min=MIN(ID) from xx
select #max=MAX(ID) from xx
while #min<#max begin
if not exists(select 1 from XX where id = #min+1) BEGIN
print 'GAP: '+ cast(#min +1 as varchar(10))
END
set #min=#min+1
end
result:
GAP: 3
GAP: 6
GAP: 7
GAP: 8
GAP: 9
First, I agree with the comments that you shouldn't try filling in holes. You won't be able to find all the holes with a single SQL statement. You'll have to loop through all possible numbers starting with 1 until you find a hole. You could write a sql function to do this for you that could then be used in a function. So if you wrote a function called find_first_hole you could then call it in an insert like:
INSERT INTO xx (id, ...) VALUES (find_first_hole(), ...)
This is a gaps&island problem, see my (and other) replies here and here. In most cases, gaps&islands problems are most elegantly solved using recursive CTE's, which are not available in mysql.
Can someone show me a sample SQL server script that I can look at that uses the "With Clause"?
I am trying to use this clause to iterate through 200 databases that contain the same table that I am trying to run a query on. I am trying to avoid using a cursor because the query time takes too long as well as using a while a loop.
Can someone advise me as to what I can do.
Thank you.
Just a poke, but here's another way to write FizzBuzz :)
100 rows is enough to show the WITH statement, I reckon.
;WITH t100 AS (
SELECT n=number
FROM master..spt_values
WHERE type='P' and number between 1 and 100
)
SELECT
ISNULL(NULLIF(
CASE WHEN n % 3 = 0 THEN 'Fizz' Else '' END +
CASE WHEN n % 5 = 0 THEN 'Buzz' Else '' END, ''), RIGHT(n,3))
FROM t100
But the real power behind WITH (known as Common Table Expression http://msdn.microsoft.com/en-us/library/ms190766.aspx "CTE") in SQL Server 2005 and above is the Recursion, as below where the table is built up through iterations adding to the virtual-table each time.
;WITH t100 AS (
SELECT n=1
union all
SELECT n+1
FROM t100
WHERE n < 100
)
SELECT
ISNULL(NULLIF(
CASE WHEN n % 3 = 0 THEN 'Fizz' Else '' END +
CASE WHEN n % 5 = 0 THEN 'Buzz' Else '' END, ''), RIGHT(n,3))
FROM t100
To run a similar query in all database, you can use the undocumented sp_msforeachdb. It has been mentioned in another answer, but it is sp_msforeachdb, not sp_foreachdb.
Be careful when using it though, as some things are not what you expect. Consider this example
exec sp_msforeachdb 'select count(*) from sys.objects'
Instead of the counts of objects within each DB, you will get the SAME count reported, begin that of the current DB.
To get around this, always "use" the database first. Note the square brackets to qualify multi-word database names.
exec sp_msforeachdb 'use [?]; select count(*) from sys.objects'
For your specific query about populating a tally table, you can use something like the below. Not sure about the DATE column, so this tally table has only the DBNAME and IMG_COUNT columns, but hope it helps you.
create table #tbl (dbname sysname, img_count int);
exec sp_msforeachdb '
use [?];
if object_id(''tbldoc'') is not null
insert #tbl
select ''?'', count(*) from tbldoc'
select * from #tbl
There are two types of WITH clauses:
Here is the FizzBuzz in SQL form, using a WITH common table expression (CTE).
;WITH mil AS (
SELECT TOP 1000000 ROW_NUMBER() OVER ( ORDER BY c.column_id ) [n]
FROM master.sys.all_columns as c
CROSS JOIN master.sys.all_columns as c2
)
SELECT CASE WHEN n % 3 = 0 THEN
CASE WHEN n % 5 = 0 THEN 'FizzBuzz' ELSE 'Fizz' END
WHEN n % 5 = 0 THEN 'Buzz'
ELSE CAST(n AS char(6))
END + CHAR(13)
FROM mil
Here is a select statement also using a WITH clause
SELECT * FROM orders WITH (NOLOCK) where order_id = 123
Try the sp_foreachdb procedure.