How can I sort this data numerically rather than lexicographically?
100_10A
100_10B
100_10C
100_11A
100_11B
100_11C
100_12A
100_12B
100_12C
100_13A
100_13B
100_13C
100_14A
100_14B
100_14C
100_15A
100_15B
100_15C
100_16A
100_16B
100_16C
100_1A
100_1B
100_1C
100_2A
100_2B
100_2C
100_3A
100_3B
100_3C
100_4A
100_4B
100_4C
100_5A
100_5B
100_5C
100_6A
100_6B
100_6C
100_7A
100_7B
100_7C
100_8A
100_8B
100_8C
100_9A
100_9B
100_9C
select generalcolum from mytable order by blockid, plotid ASC
What I need out of this sort order is
100_1A
100_1B
100_1C...
...
...
100_10A
100_10B
100_10C
What I need to do in some way is have a zero added before the sort happens so that, I can get them in the order I want.
There are two colums, one that stores the 100 (number before the underscore) and one that stores the 1A the value after the underscore.
My sudo crap select
select thiscolum this table
order by blockid, plotid(+1 zero to prefix if len(plotid) < 2)
For example if the plot value is 1A, to do the best sorting, i need it to be looked at as 01A so that it comes before 10A.
order by length(blockid), blockid, length(plotid), plotid
Related
I have a table in mysql. Table Name is constitutive_table, it contains more than 40 columns and its type is varchar, it contains more than 25000 records. I wrote the query like this to get the 10 least value. But it showing like as you have seen in the picture.
SELECT `Sequence_Name`
, `Name_of_the_Protein`
, `Brain`
FROM `constitutive_table`
where `Brain` != 0
ORDER
BY cast(Brain AS int)
LIMIT 0,10
The data in the Brain column appears to be floating point, so you should be casting to the appropriate type:
SELECT Sequence_Name, Name_of_the_Protein, Brain
FROM constitutive_table
WHERE CAST(Brain AS DECIMAL(14, 8)) <> 0
ORDER BY CAST(Brain AS DECIMAL(14, 8))
LIMIT 10
Most likely what is happening now is that the 10 values you see all have the same value when cast to integer. As a result, MySQL is using some secondary sort to generate the order you do see.
While the above query may resolve your problem, ideally you should change the Brain column to some numeric type.
I am having 10 sets of strings each set having 9 strings. Of this 10 sets, all strings in first set have length 10, those in second set have length 9 and so on. Finally, all strings in 10th set have length 1.
There is common prefix of (length-2) characters in each set. And the prefix length reduces by 1 in next set. Thus, first set has 8 characters in common, second has 7 and so on.
Here is what a sample of 10 sets look like:
pu3q0k0vwn
pu3q0k0vwp
pu3q0k0vwr
pu3q0k0vwq
pu3q0k0vwm
pu3q0k0vwj
pu3q0k0vtv
pu3q0k0vty
pu3q0k0vtz
pu3q0k0vw
pu3q0k0vy
pu3q0k0vz
pu3q0k0vx
pu3q0k0vr
pu3q0k0vq
pu3q0k0vm
pu3q0k0vt
pu3q0k0vv
pu3q0k0v
pu3q0k0y
pu3q0k1n
pu3q0k1j
pu3q0k1h
pu3q0k0u
pu3q0k0s
pu3q0k0t
pu3q0k0w
pu3q0k0
pu3q0k2
pu3q0k3
pu3q0k1
pu3q07c
pu3q07b
pu3q05z
pu3q0hp
pu3q0hr
pu3q0k
pu3q0m
pu3q0t
pu3q0s
pu3q0e
pu3q07
pu3q05
pu3q0h
pu3q0j
pu3q0
pu3q2
pu3q3
pu3q1
pu3mc
pu3mb
pu3jz
pu3np
pu3nr
pu3q
pu3r
pu3x
pu3w
pu3t
pu3m
pu3j
pu3n
pu3p
pu3
pu9
pud
pu6
pu4
pu1
pu0
pu2
pu8
pu
pv
0j
0h
05
pg
pe
ps
pt
p
r
2
0
b
z
y
n
q
Requirement:
I have a table PROFILES having columns SRNO (type bigint, primary key) and UNIQUESTRING (type char(10), unique key). I want to find 450 SRNOs for matching UNIQUESTRINGs from those 10 sets.
First find strings like in the first set. If we don't get enough results (ie. 450), find strings like in second set. If we still don't get enough results (450 minus results of first set) find strings like in third set. And so on.
Existing Solution:
I've written query something like:
select srno from profiles
where ( (uniquestring like 'pu3q0k0vwn%')
or (uniquestring like 'pu3q0k0vwp%') -- all those above uniquestrings after this and finally the last one
or (uniquestring like 'n%')
or (uniquestring like 'q%')
)
limit 450
However, after getting feedback from Rick James in this answer I realized this is not optimized query as it touches lot many rows than it needs.
So I plan to rewrite the query like this:
(select srno from profiles where uniquestring like 'pu3q0k0vwn%' LIMIT 450)
UNION DISTINCT
(select srno from profiles where uniquestring like 'pu3q0k0vwp%' LIMIT 450); -- and more such clauses after this for each uniquestring
I like to know if there are any better solutions to do this.
SELECT ...
WHERE str LIKE 'pu3q0k0vw%' AND -- the 10-char set
str REGEXP '^pu3q0k0vw[nprqmj]' -- the 9 next letters
LIMIT ...
# then check for 450; if not enough, continue...
SELECT ...
WHERE str LIKE 'pu3q0k0vt%' AND -- the 10-char set
str REGEXP '^pu3q0k0vt[vyz]' -- the 9 next letters
LIMIT 450
# then check for 450; if not enough, continue...
etc.
SELECT ...
WHERE str LIKE 'pu3q0k0v%' AND -- the 9-char set
str REGEXP '^pu3q0k0v[wyzxrqmtv]' -- the 9 next letters
LIMIT ...
# check, etc; for a total of 10 SELECTs or 450 rows, whichever comes first.
This will be 10+ selects. Each select will be somewhat optimized by first picking rows with a common prefix with LIKE, then it double checks with a REGEXP.
(If you don't like splitting the inconsistent pu3q0k0vw vs. pu3q0k0vt; we can discuss things further.)
You say "prefix"; I have coded the LIKE and REGEXP to assume arbitrary text after the prefix given.
UNION is not viable, since it will (I think) gather all the rows before picking 450. Each SELECT will stop at the LIMIT if there is no DISTINCT GROUP BY or ORDER BY that require gathering everything first.
REGEXP is not smart enough to avoid scanning the entire table; adding the LIKE avoids such (except when more than, say, 20% of the rows match the LIKE).
I've got a database with a column that contains the following data:
aaa-1
aaa-2
aaa-3
...
aaa-10
aaa-11
...
aaa-100
aaa-101
...
aaa-1000
When I query and sort the data in ascending order, I get:
aaa-1
aaa-10
aaa-11
...
aaa-100
aaa-101
...
aaa-1000
...
aaa-2
...
aaa-3
Is this actually the correct (machine) way of sorting? Is the order being screwed up because of the aaa- prefix? How do I go about sorting this the way a human would (ie something that looks like the first snippet)?
P.S. If the problem does lie in the prefix, is there a way to remove it and sort with just the numeric component?
P.P.S. It's been suggested to me that I should just change my data and add leading zeroes like aaa-0001 and aaa-0002, etc. However, I'm loathe to go that method as each time the list goes up an order of 10, I'd have to reformat this column.
Thank you all in advance! :)
You can extract the number part, convert it to numeric data type and then do an ORDER BY:
SELECT mytable.*,
CAST(SUBSTRING_INDEX(mycolumn, '-', - 1) AS UNSIGNED) mycolumnintdata
FROM
mytable
ORDER BY mycolumnintdata;
If there are expressions which does not match number, the CAST function would return 0 and those records would be displayed first. You may handle this separately if needed.
I had a similar issue and the trick that did it for me was this one
*"ORDER BY LENGTH(column_name), column_name
As long as the non-numeric part of the value is the same length, this will sort 1 before 10, 10 before 100, etc."*
as given by Andreas Bergström on this question.
Hope that helps someone.
this is the alphabetical order,
you want numerical order,
for do this you must in the ORDER BY clause
trim the costant "aaa-" part
convert it in number
convert(SUBSTRING(val, 3), integer)
I will give you a sample sorting. Not based on your data sample, but this could help you out.
Say you have data like this :
id
----
1
2
6
10
13
when you do ORDER BY id ASC would return :
id
----
1
10
13
2
6
I suggest, use LPAD.
This query : SELECT LPAD('12',5,'0') return 00012
So when you have table data like I provide above, you can sort them like this :
SELECT * FROM TABLE
ORDER BY LPAD(ID,7,'0') ASC
Based on your data.
SELECT SUBSTR('aaa-100',5,LENGTH('aaa-100') - 3) return 100
So, SELECT LPAD( SUBSTR('aaa-100',5,LENGTH('aaa-100') - 3), 7, '0') return 00000100
So you can combine string function such as SUBSTR and LPAD. Do have any clue now?
Current SQL: SELECT code FROM myTable ORDER BY code ASC
code
---
11
113
12
13A
This is the current order I have of a MySQL table.
I want the order to be A-Z, 1-10 however, numerically, like this:
code
---
11
12
13A
113
The reason I cannot achieve this effect in the first place is because the code column is varchar and not int. However as shown in the example, some codes have a letter prepended to them so I cannot change this to integer.
How can I get around this problem without changing the data type?
The simplest way is to use silent conversion. Just add 0:
order by code + 0
In practice, you might want:
order by code + 0, code
This should work, sorting by number first and alpha after (if the same number):
select * from myTable
order by cast(replace(code,'[0-9]+','') as unsigned), code
See this SQL Fiddle
Let's say I have a list of values, like this:
id value
----------
A 53
B 23
C 12
D 72
E 21
F 16
..
I need the top 10 percent of this list - I tried:
SELECT id, value
FROM list
ORDER BY value DESC
LIMIT COUNT(*) / 10
But this doesn't work. The problem is that I don't know the amount of records before I do the query. Any idea's?
Best answer I found:
SELECT*
FROM (
SELECT list.*, #counter := #counter +1 AS counter
FROM (select #counter:=0) AS initvar, list
ORDER BY value DESC
) AS X
where counter <= (10/100 * #counter);
ORDER BY value DESC
Change the 10 to get a different percentage.
In case you are doing this for an out of order, or random situation - I've started using the following style:
SELECT id, value FROM list HAVING RAND() > 0.9
If you need it to be random but controllable you can use a seed (example with PHP):
SELECT id, value FROM list HAVING RAND($seed) > 0.9
Lastly - if this is a sort of thing that you need full control over you can actually add a column that holds a random value whenever a row is inserted, and then query using that
SELECT id, value FROM list HAVING `rand_column` BETWEEN 0.8 AND 0.9
Since this does not require sorting, or ORDER BY - it is O(n) rather than O(n lg n)
You can also try with that:
SET #amount =(SELECT COUNT(*) FROM page) /10;
PREPARE STMT FROM 'SELECT * FROM page LIMIT ?';
EXECUTE STMT USING #amount;
This is MySQL bug described in here: http://bugs.mysql.com/bug.php?id=19795
Hope it'll help.
I realize this is VERY old, but it still pops up as the top result when you google SQL limit by percent so I'll try to save you some time. This is pretty simple to do these days. The following would give the OP the results they need:
SELECT TOP 10 PERCENT
id,
value
FROM list
ORDER BY value DESC
To get a quick and dirty random 10 percent of your table, the following would suffice:
SELECT TOP 10 PERCENT
id,
value
FROM list
ORDER BY NEWID()
I have an alternative which hasn't been mentionned in the other answers: if you access from any language where you have full access to the MySQL API (i.e. not the MySQL CLI), you can launch the query, ask how many rows there will be and then break the loop if it is time.
E.g. in Python:
...
maxnum = cursor.execute(query)
for num, row in enumerate(query)
if num > .1 * maxnum: # Here I break the loop if I got 10% of the rows.
break
do_stuff...
This works only with mysql_store_result(), not with mysql_use_result(), as the latter requires that you always accept all needed rows.
OTOH, the traffic for my solution might be too high - all rows have to be transferred.