Imagine we have following table
create table t
(item number,
bin number,
primary key (bin , item) );
I have used insert into command to insert several values into table t, now i am interested in what does this code
select * from t
order by 1,2;
As far as i know it selects everything from table t and sorts it, because order means to sort selected query using condition listed in order command, but order 1,2 i could not understand what does it means, could you help me ?
It sorts the result by the first and second column, so in your case it's identical to
select *
from t
order by item, bin;
It will order the results by the first column, and then, if there are some rows with the same value in the first column it will order them by the second column.
select * from t
order by item, bin; // just different written but result is same.
Result will be sorted by first and second column.
Difference is in readability of code so if someone don't know information about table, your select says nothing him. Person only knows that result will be sorted by 1. and 2. column, nothing more.
It's the same as regular ORDER BY clause but kind of assigns numeric aliases to the column names.
In your case, 1 = 'item number' and 2 = 'bin number'.
Same as:
SELECT * FROM t
ORDER BY item number, bin number;
Related
I've spent an inordinate amount of time this morning trying to Google what I thought would be a simple thing. I need to set up an SQL query that selects multiple columns, but only returns one instance if one of the columns (let's call it case_number) returns duplicate rows.
select case_number, name, date_entered from ticket order by date_entered
There are rows in the ticket table that have duplicate case_number, so I want to eliminate those duplicate rows from the results and only show one instance of them. If I use "select distinct case_number, name, date_entered" it applies the distinct operator to all three fields, instead of just the case_number field. I need that logic to apply to only the case_number field and not all three. If I use "group by case_number having count (*)>1" then it returns only the duplicates, which I don't want.
Any ideas on what to do here are appreciated, thank you so much!
You can use ROW_NUMBER(). For example
select *
from (
select *,
row_number() over(partition by case_number) as rn
) x
where rn = 1
The query above will pseudo-randomly pick one row for each case_number. If you want a better selection criteria you can add ORDER BY or window frames to the OVER clause.
I need help on creating a select statement in sql to get the unique rows.
I need the unique Reference ID but since Call Time is also unique, I only need to get the first row out of the similar rows.
I have this table[Calls]:
The result should be:
When I used:
Select Distinct * FROM Calls
It will return the same table and not the result I want.
It may helps you...
min(date) is the first datetime for each individual
Select referenceid,min(date),number from calls
group by referenceid,number
Perhaps a simple GROUP BY:
SELECT ReferenceID,
MIN(CallTime) AS CallTime,
MIN(Number) AS Number
FROM dbo.TableName t
GROUP BY ReferenceID
I have three columns in one table (code, code alt and product). Code column has duplicate data. I want to leave all results without repeating the code column. I try with this
Select code, code alt, product from table
where code in
(
select code from table
group by code
having count (code)=1
)
but do not appear all results.
Thanks
If you want to leave only one row with the particular code from the bunch of rows with the same code you need to decide which one from multiple rows you want to leave.
You need some criteria by which you will be able to rank rows with the same code and select one from them by higher (for example) rank value. The script below will leave only one - random - row with specific code.
This is just an example that shows you the idea and it intended for SQL Server - because you do not pointed your DBMS
with [src] as (
select code, [code alt], product, rank() over(partition by code order by newid()) [rank]
from [table])
select * from [src] where [rank] = 1
Ranking Functions
I realize my title probably doesnt explain my situation very well, but I honestly have no idea how to word this.
I am using SQL to access a DB2 database.
Using my screenshot image 1 below as a reference:
column 1 has three instances of "U11124", with three different descriptions (column 2)
I would like this query to return the first instance of "U11124" and its description, but then also unique records for the other rows. image 2 shows my desired result.
image 1
image 2
----- EDIT ----
to answer some of the questions / posts:
technically, it does not need to be the first , just any single one of those records. the problem is that we have three descriptions, and only one needs to be shown, i am now told it does not matter which one.
SELECT STVNST, MAX(STDESC) FROM MY_TABLE GROUP BY STVNST;
In SQL Server:
select stvnst, stdesc
from (
select
stvnst, stdesc
row_number() over (order by stdesc partition by stvnst) row
from table
) a
where row = 1
This method has an advantage over a simple group by, in that it will also work when there's more than two columns in the table.
SELECT STVNST,FIRST(STDESC) from table group by STVNST ORDER BY what_you_want_first
All you need to do is use GROUP BY.
You say you want the first instance of the STDESC column? Well you can't guarntee the order of the rows without another column, however if you want to order by the highest ordered value the following will suffice:
SELECT STVNST, MAX(STDESC) FROM MY_TABLE GROUP BY STVNST;
What is the most efficient way to select the first and last element only, from a column in SQLite?
The first and last element from a row?
SELECT column1, columnN
FROM mytable;
I think you must mean the first and last element from a column:
SELECT MIN(column1) AS First,
MAX(column1) AS Last
FROM mytable;
See http://www.sqlite.org/lang_aggfunc.html for MIN() and MAX().
I'm using First and Last as column aliases.
if it's just one column:
SELECT min(column) as first, max(column) as last FROM table
if you want to select whole row:
SELECT 'first',* FROM table ORDER BY column DESC LIMIT 1
UNION
SELECT 'last',* FROM table ORDER BY column ASC LIMIT 1
The most efficient way would be to know what those fields were called and simply select them.
SELECT `first_field`, `last_field` FROM `table`;
Probably like this:
SELECT dbo.Table.FirstCol, dbo.Table.LastCol FROM Table
You get minor efficiency enhancements from specifying the table name and schema.
First: MIN() and MAX() on a text column gives AAAA and TTTT results which are not the first and last entries in my test table. They are the minimum and maximum values as mentioned.
I tried this (with .stats on) on my table which has over 94 million records:
select * from
(select col1 from mitable limit 1)
union
select * from
(select col1 from mitable limit 1 offset
(select count(0) from mitable) -1);
But it uses up a lot of virtual machine steps (281,624,718).
Then this which is much more straightforward (which works if the table was created without WITHOUT ROWID) [sql keywords are in capitals]:
SELECT col1 FROM mitable
WHERE ROWID = (SELECT MIN(ROWID) FROM mitable)
OR ROWID = (SELECT MAX(ROWID) FROM mitable);
That ran with 55 virtual machine steps on the same table and produced the same answer.
min()/max() approach is wrong. It is only correct, if the values are ascending only. I needed something liket this for currency rates, which are random raising and falling.
This is my solution:
select st.*
from stats_ticker st,
(
select min(rowid) as first, max(rowid) as last --here is magic part 1
from stats_ticker
-- next line is just a filter I need in my case.
-- if you want first/last of the whole table leave it out.
where timeutc between datetime('now', '-1 days') and datetime('now')
) firstlast
WHERE
st.rowid = firstlast.first --and these two rows do magic part 2
OR st.rowid = firstlast.last
ORDER BY st.rowid;
magic part 1: the subselect results in a single row with the columns first,last containing rowid's.
magic part 2 easy to filter on those two rowid's.
This is the best solution I've come up so far. Hope you like it.
We can do that by the help of Sql Aggregate function, like Max and Min. These are the two aggregate function which help you to get last and first element from data table .
Select max (column_name ), min(column name) from table name
Max will give you the max value means last value and min will give you the min value means it will give you the First value, from the specific table.