I was thinking about simple reordering rows in relational database's table.
I would like to avoid method described here:
How can I reorder rows in sql database
My simple idea was to use as ListOrder column of type double-precision 64-bit IEEE 754 floating point.
At inserting a row between two existing rows we calculate listOrder value as average of these sibling elements.
Example:
1. Starting state:
value, listOrder
a 1
b 2
c 3
d 4
e 5
f 6
2. Moving "e" two rows up
One simple sql update on e-row: update mytable set listorder=2.5 where value='e'
value, listOrder
a 1
b 2
e 2.5
c 3
d 4
f 6
3. Moving "a" one position down
value, listOrder
b 2
a 2.25
e 2.5
c 3
d 4
f 6
I have a question. How many insertions can I perform (in the edge situation) to have properly ordered list.
For the 64 bit integer there is less than 64 insertions in the same place.
Is floating point types allows to more insertions?
There are other problems with described approach?
Do you see any patches/adjustments to make this idea safe and usable in applications?
This is similar to a lexical order, which can also be done with varchar columns:
A
B
C
D
E
F
becomes
A
B
BM
C
D
F
becomes
B
BF
BM
C
D
F
I prefer the two step process, where you update every row in the table after the one you move to be one larger. Sql is efficient about this, where updating the rows following a change is not as bad as it seems. You preserve something that's more human readable, the storage size for your ordinal value scales in a linear rather with your data size, and you don't risk coming to a point where you don't have enough precision to put an item in between two values
Related
I'm looking to replicate this randomisation in R studio.
Key features:
A and B are the primary comparison and must have 2 by 2 cross over design (i.e., occur togeather in each sequence)
The incomplete block design should include C D E and F - comparisons of interest are C vs D and E vs F. These comparisons need to occur the same number of times within the whole design, and one comparison must occur in each sequence
C D E F need to be balanced so that they occur the same number of times in a sequence
C D E F need to be balanced so that occurr the same number of times across periods
Any help would be greatly appreciated.
Many thanks.
The code I tried below is just for the incomplete block design C,D,E,F but I can't get it to balance across periods.
library(crossdes)
out=find.BIB(4,20,3, iter=1)#each dosed 6 times achieving first order balance
out
isGYD(out)
I had then planned to join on the A and B rand.
Suppose I have a table as follows:
id name length
1 A 21.5
2 B 12.4
3 C 0
4 D 17
5 E 1
I wish to get:
id name length
1 A 21.5
5 E 1
Meaning all rows that hase length that ends up with 1.
length is a numeric column.
It's very simple thing to do with programing languages but it seems quite not natural for SQL. How can I do that efficiently and simply?
My only thought is to convert the field to Text and then lose eveything after the . then convert it to array and choose the letter in the position of array length. This will probebly work but it seems like a very bad solution.
You can use FLOOR and modulo division:
SELECT *
FROM tab
WHERE FLOOR(length) % 10 = 1;
SqlFiddleDemo
I have two dataset data1 and data2
data data1;
input sn id $;
datalines;
1 a
2 a
3 a
;
run;
data data2;
input id $ sales x $;
datalines;
a 10 x
a 20 y
a 30 z
a 40 q
;
run;
I am merging them from below code:
data join;
merge data1(in=a) data2(in=b);
by id;
if a and b;
run;
Result: (I was expecting an Inner Join result which is not the case)
1 a 10 x
2 a 20 y
2 a 30 z
2 a 40 w
Result from proc sql inner join.
proc sql;
select data1.id,sn,sales,x from data2 inner join data1 on data1.hh_id;
quit;
Result: (As expected from an inner join)
a 1 10 x
a 1 20 y
a 1 30 z
a 1 40 w
a 2 10 x
a 2 20 y
a 2 30 z
a 2 40 w
b 3 10 x
b 3 20 y
b 3 30 z
b 3 40 w
I want to know the concept and STEP BY STEP working of merge statement in SAS with In= and proving the above result.
PS: I have read this, and it says
An obvious use for these variables is to control what kind of 'merge'
will occur, using if statements. For example, if
ThisRecordIsFromYourData and ThisRecordIsFromOtherData; will make SAS
only include rows that match on the by variables from both input data
sets (like an inner join).
which I guess, (like an Inner Join) is not always the case.
Basically, this is a result of the difference in how the SAS data step and SQL process their respective join/merges.
SQL creates a separate record for each possible combination of keys. This is a Cartesian Product (at the key level).
SAS data step, however, process merges very differently. MERGE is really nothing more than a special case of SET. It still processes rows iteratively, one at a time - it never goes back, and never has more than one row from any dataset in the PDV at once. Thus, it cannot create a Cartesian product in its normal process - that would require random access, which the SAS datastep doesn't do normally.
What it does:
For each unique BY value
Take the next record from the left side dataset, if one exists with that BY value
Take the next record from the right side dataset, if one exists with that BY value
Output a row
Continue until both datasets are exhausted for that BY value
With BY values that yield unique records per value on either side (or both), it is effectively identical to SQL. However, with BY values that yield duplicates on BOTH sides, you get what you have there: a side-by-side merge, and if one runs out before the other, the values from the last row of the shorter dataset (for that by value) are more-or-less copied down. (They're actually RETAINED, so if you overwrite them with changes, they will not reset on new records from the longer dataset).
So, if left has 3 records and right has 4 records for key value a, like in your example, then you get data from the following records (assuming you don't alter the data after):
left right
1 1
2 2
3 3
3 4
I want to combine multiple lists of items into a single list, retaining the overall order requirements. i.e.:
1: A C E
2: D E
3: B A D
result: B A C D E
above, starting with list 1, we have ACE, we then know that D must come before E, and from list 3, we know that B must come before A, and D must come after B and A.
If there are conflicting orderings, the first ordering should be used. i.e.
1: A C E
2: B D E
3: F D B
result: A C F B D E
3 conflicts with 2 (B D vs D B), therefore requirements for 2 will be used.
If ordering requirements mean an item must come before or after another, it doesn't matter if it comes immediately before or after, or at the start or end of the list, as long as overall ordering is maintained.
This is being developed using VB.Net, so a LINQy solution (or any .Net solution) would be nice - otherwise pointers for an approach would be good.
Edit: Edited to make example 2 make sense (a last minute change had made it invalid)
The keyword you are probably interested in is "Topological sorting". The solution based on that would look as follows:
Create an empty directed graph.
Process sequences in order, for each two consecutive elements X,Y in a sequence add an edge X->Y to the graph, unless this would form a cycle.
Perform a topological sort on the vertices of the graph. The resulting sequence should satisfy your requirements.
Total newbie here, regarding sqlite, so don't flame too hard :)
I have a table:
index name length L breadth B height H
1 M-1234 10 5 2
2 M-2345 20 10 3
3 ....
How do I put some tabular data (let' say ten x,y values) corresponding to index 1, then another table to index 2, and then another, etc. In short, so that I have a table of x and y values that is "connected" to first row, then another that is connected to second row.
I'm reading some tutorials on sqlite3 (which I'm using), but am having trouble finding this. If anyone knows a good newbie tutorial or a book dealing with sqlite3 (CLI) I'm all ears for that too :)
You are just looking for information on joins and the concept of foreign key, that although SQLite3 doesn't enforce, is what you need. You can go without it, anyway.
In your situation you can either add two "columns" to your table, being one x and another y, or create a new table with 3 "columns": foreign_index, x and y. Which one to use depends on what you are trying to accomplish, performance and maintainability.
If you go the linked table route, you'd end up with two tables, like this:
MyTable
index name length L breadth B height H
1 M-1234 10 5 2
2 M-2345 20 10 3
3 ....
XandY
foreign_index x y
1 12 9
2 8 7
3 ...
When you want the x and y values of your element, you just use something like SELECT x, y FROM XandY WHERE foreign_index = $idx;
To get all the related attributes, you just do a JOIN:
SELECT index, name, length, breadth, height, x, y FROM MyTable INNER JOIN XandY ON MyTable.index = XandY.foreign_index;