I'm using Oracle SQL and i need some help with a query.
In the following query i'm selecting some rows with a simple condition (never mind hat kind of). From the output rows, i need to select the row with minimum value of DATE. For that, i'm using ROWNUM.
SELECT *
FROM(
SELECT NAME, DATE
FROM LIST
WHERE NAME = 'BLABLA'
ORDER by DATE)
WHERE ROWNUM = 1;
However, this query must fit to any other SQL languages, and therefore i need to write this query without ROWNUM.
Is there a simple way to write this query without using ROWNUM?
Unfortunately, row limit syntax differs between RDBMS.
The following is portable between SqlServer, Oracle and PostGres:
SELECT *
FROM (
SELECT NAME, DATE, ROW_NUMBER() OVER (ORDER by DATE) AS RowNum
FROM LIST
WHERE NAME = 'BLABLA'
) X
WHERE RowNum = 1;
However, other DB's syntax is different, e.g. MySql's LIMIT
select * from LIST
where Date=(select min(date) from LIST where Name='BLABLA' )
and Name='BLABLA'
Related
Is there a way to make a simple GROUP BY query with SQL and not use COUNT,AVG or SUM? I want to show all columns and group it with a single column.
SELECT * FROM [SPC].[dbo].[BoardSFC] GROUP BY boardsn
The query above is working on Mysql but not on SQL, is there a way to achieve this? any suggestion would be great
UPDATE: Here is my data I just need to group them by boardsn and get imulti equals to 1
I thing you just understand 'group data' in a different way than it is implemented in sql server. You simply want rows that have the same value together in the result and that would be ordering not grouping. So maybe what you need is:
SELECT *
FROM [SPC].[dbo].[BoardSFC]
WHERE imulti = 1
ORDER BY boardsn
The query above is working on Mysql but not on SQL, is there a way to achieve this? any suggestion would be great
No, there is not. MySQL only lets you do this because it violates the various SQL standards quite egregiously.
You need to name each column you want in the result-set whenever you use GROUP BY. The SELECT * feature is only provided as a convenience when working with data interactively - in production code you should never use SELECT *.
You could use a TOP 1 WITH TIES combined with a ORDER BY ROW_NUMBER.
SELECT TOP 1 WITH TIES *
FROM [SPC].[dbo].[BoardSFC]
ORDER BY ROW_NUMBER() OVER (PARTITION BY boardsn ORDER BY imulti)
Or more explicitly, use ROW_NUMBER in a sub-query
SELECT *
FROM
(
SELECT *, ROW_NUMBER() OVER (PARTITION BY boardsn ORDER BY imulti) as RN
FROM [SPC].[dbo].[BoardSFC]
) q
where RN = 1
I want to fire a Query "SELECT * FROM TABLE" but select only from row N+1. Any idea on how to do this?
For SQL Server 2012 and above, use this:
SELECT *
FROM Sales.SalesOrderHeader
ORDER BY OrderDate
OFFSET (#Skip) ROWS FETCH NEXT (#Take) ROWS ONLY
https://stackoverflow.com/a/19669165/1883345
SQL Server:
select * from table
except
select top N * from table
Oracle up to 11.2:
select * from table
minus
select * from table where rownum <= N
with TableWithNum as (
select t.*, rownum as Num
from Table t
)
select * from TableWithNum where Num > N
Oracle 12.1 and later (following standard ANSI SQL)
select *
from table
order by some_column
offset x rows
fetch first y rows only
They may meet your needs more or less.
There is no direct way to do what you want by SQL.
However, it is not a design flaw, in my opinion.
SQL is not supposed to be used like this.
In relational databases, a table represents a relation, which is a set by definition. A set contains unordered elements.
Also, don't rely on the physical order of the records. The row order is not guaranteed by the RDBMS.
If the ordering of the records is important, you'd better add a column such as `Num' to the table, and use the following query. This is more natural.
select *
from Table
where Num > N
order by Num
Query: in sql-server
DECLARE #N INT = 5 --Any random number
SELECT * FROM (
SELECT ROW_NUMBER() OVER(ORDER BY ID) AS RoNum
, ID --Add any fields needed here (or replace ID by *)
FROM TABLE_NAME
) AS tbl
WHERE #N < RoNum
ORDER BY tbl.ID
This will give rows of Table, where rownumber is starting from #N + 1.
In order to do this in SQL Server, you must order the query by a column, so you can specify the rows you want.
Example:
select * from table order by [some_column]
offset 10 rows
FETCH NEXT 10 rows only
Do you want something like in LINQ skip 5 and take 10?
SELECT TOP(10) * FROM MY_TABLE
WHERE ID not in (SELECT TOP(5) ID From My_TABLE ORDER BY ID)
ORDER BY ID;
This approach will work in any SQL version. You need to stablish some order (by Id for example) so all rows are provided in a predictable manner.
I know it's quite late now to answer the query. But I have a little different solution than the others which I believe has better performance because no comparisons are performed in the SQL query only sorting is done. You can see its considerable performance improvement basically when value of SKIP is LARGE enough.
Best performance but only for SQL Server 2012 and above. Originally from #Majid Basirati's answer which is worth mentioning again.
DECLARE #Skip INT = 2, #Take INT = 2
SELECT * FROM TABLE_NAME
ORDER BY ID ASC
OFFSET (#Skip) ROWS FETCH NEXT (#Take) ROWS ONLY
Not as Good as the first one but compatible with SQL Server 2005 and above.
DECLARE #Skip INT = 2, #Take INT = 2
SELECT * FROM
(
SELECT TOP (#Take) * FROM
(
SELECT TOP (#Take + #Skip) * FROM TABLE_NAME
ORDER BY ID ASC
) T1
ORDER BY ID DESC
) T2
ORDER BY ID ASC
What about this:
SELECT * FROM table LIMIT 50 OFFSET 1
This works with all DBRM/SQL, it is standard ANSI:
SELECT *
FROM owner.tablename A
WHERE condition
AND n+1 <= (
SELECT COUNT(DISTINCT b.column_order)
FROM owner.tablename B
WHERE condition
AND b.column_order>a.column_order
)
ORDER BY a.column_order DESC
PostgreSQL: OFFSET without LIMIT
This syntax is supported, and it is in my opinion the cleanest API compared to other SQL implementations as it does not introduce any new keywords:
SELECT * FROM mytable ORDER BY mycol ASC OFFSET 1
that should definitely be standardized.
The fact that this is allowed can be seen from: https://www.postgresql.org/docs/13/sql-select.html since LIMIT and OFFSET can be given independently, since OFFSET is not a sub-clause of LIMIT in the syntax specification:
[ LIMIT { count | ALL } ]
[ OFFSET start [ ROW | ROWS ] ]
SQLite: negative limit
OFFSET requires LIMIT in that DBMS, but dummy negative values mean no limit. Not as nice as PostgreSQL, but it works:
SELECT * FROM mytable ORDER BY mycol ASC LIMIT -1 OFFSET 1
Asked at: SQLite with skip (offset) only (not limit)
Documented at: https://sqlite.org/lang_select.html
If the LIMIT expression evaluates to a negative value, then there is no upper bound on the number of rows returned.
MySQL: use a huge limit number
Terrible API design, the documentation actually recommends it:
SELECT * FROM tbl LIMIT 1,18446744073709551615;
Asked at: MySQL skip first 10 results
Node.js Sequelize ORM implements it
That ORM allows e.g. findAll({offset: without limit:, and implements workarounds such as the ones mentioned above for each different DBMS.
In Faircom SQL (which is a pseudo MySQL), i can do this in a super simple SQL Statement, just as follows:
SELECT SKIP 10 * FROM TABLE ORDER BY Id
Obviously you can just replace 10 with any declared variable of your desire.
I don't have access to MS SQL or other platforms, but I'll be really surprised MS SQL doesn't support something like this.
DECLARE #Skip int= 2, #Take int= 2
SELECT * FROM TABLE_NAME
ORDER BY Column_Name
OFFSET (#Skip) ROWS FETCH NEXT (#Take) ROWS ONLY
try below query it's work
SELECT * FROM `my_table` WHERE id != (SELECT id From my_table LIMIT 1)
Hope this will help
You can also use OFFSET to remove the 1st record from your query result like this-
Example - find the second max salary from the employee table
select distinct salary from employee order by salary desc limit 1 OFFSET 1
For SQL Server 2012 and later versions, the best method is #MajidBasirati's answer.
I also loved #CarlosToledo's answer, it's not limited to any SQL Server version but it's missing Order By Clauses. Without them, it may return wrong results.
For SQL Server 2008 and later I would use Common Table Expressions for better performance.
-- This example omits first 10 records and select next 5 records
;WITH MyCTE(Id) as
(
SELECT TOP (10) Id
FROM MY_TABLE
ORDER BY Id
)
SELECT TOP (5) *
FROM MY_TABLE
INNER JOIN MyCTE ON (MyCTE.Id <> MY_TABLE.Id)
ORDER BY Id
I have a page to show 10 messages by each user (don't ask me why)
I have the following code:
SELECT *, row_number() over(partition by user_id) as row_num
FROM "posts"
WHERE row_num <= 10
It doesn't work.
When I do this:
SELECT *
FROM (
SELECT *, row_number() over(partition by user_id) as row_num FROM "posts") as T
WHERE row_num <= 10
It does work.
Why do I need nested query to see row_num column? Btw, in first request I actually see it in results but can't use where keyword for this column.
It seems to be the same "rule" as any query, column aliases aren't visible to the WHERE clause;
This will also fail;
SELECT id AS newid
FROM test
WHERE newid=1; -- must use "id" in WHERE clause
SQL Query like:
SELECT *
FROM table
WHERE <condition>
will execute in next order:
3.SELECT *
1.FROM table
2.WHERE <condition>
so, as Joachim Isaksson say, columns in SELECt clause are not visible in WHERE clause, because of processing order.
In your second query, column row_num are fetched in FROM clause first, so it will be visible in WHERE clause.
Here is simple list of steps in order they executes.
There is a good reason for this rule in standard SQL.
Consider the statement:
SELECT *, row_number() over (partition by user_id) as row_num
FROM "posts"
WHERE row_num <= 10 and p.type = 'xxx';
When does the p.type = 'xxx' get evaluated relative to the row number? In other words, would this return the first ten rows of "xxx"? Or would it return the "xxx"s in the first ten rows?
The designers of the SQL language recognize that this is a hard problem to resolve. Only allowing them in the select clause resolves the issue.
You can check this topic and this one on dba.stockexchange.com about order in which SQL executes SELECT clause. I think it aplies not only for PostgreSQL, but for all RDBMS.
I have a table with n number of records
How can i retrieve the nth record and (n-1)th record from my table in SQL without using derived table ?
I have tried using ROWID as
select * from table where rowid in (select max(rowid) from table);
It is giving the nth record but i want the (n-1)th record also .
And is there any other method other than using max,derived table and pseudo columns
Thanks
You cannot depend on rowid to get you to the last row in the table. You need an auto-incrementing id or creation time to have the proper ordering.
You can use, for instance:
select *
from (select t.*, row_number() over (order by <id> desc) as seqnum
from t
) t
where seqnum <= 2
Although allowed in the syntax, the order by clause in a subquery is ignored (for instance http://docs.oracle.com/javadb/10.8.2.2/ref/rrefsqlj13658.html).
Just to be clear, rowids have nothing to do with the ordering of rows in a table. The Oracle documentation is quite clear that they specify a physical access path for the data (http://docs.oracle.com/cd/B28359_01/server.111/b28318/datatype.htm#i6732). It is true that in an empty database, inserting records into a newtable will probably create a monotonically increasing sequence of row ids. But you cannot depend on this. The only guarantees with rowids are that they are unique within a table and are the fastest way to access a particular row.
I have to admit that I cannot find good documentation on Oracle handling or not handling order by's in subqueries in its most recent versions. ANSI SQL does not require compliant databases to support order by in subqueries. Oracle syntax allows it, and it seems to work in some cases, at least. My best guess is that it would probably work on a single processor, single threaded instance of Oracle, or if the data access is through an index. Once parallelism is introduced, the results would probably not be ordered. Since I started using Oracle (in the mid-1990s), I have been under the impression that order bys in subqueries are generally ignored. My advice would be to not depend on the functionality, until Oracle clearly states that it is supported.
select * from (select * from my_table order by rowid) where rownum <= 2
and for rows between N and M:
select * from (
select * from (
select * from my_table order by rowid
) where rownum <= M
) where rownum >= N
Try this
select top 2 * from table order by rowid desc
Assuming rowid as column in your table:
SELECT * FROM table ORDER BY rowid DESC LIMIT 2
I want to implement paging in a gridview or in an html table which I will fill using ajax. How should I write queries to support paging? For example if pagesize is 20 and when the user clicks page 3, rows between 41 and 60 must be shown on table. At first I can get all records and put them into cache but I think this is the wrong way. Because data can be very huge and data can be change from other sessions. so how can I implement this? Is there any generic way ( for all databases ) ?
As others have suggested, you can use rownum in Oracle. It's a little tricky though and you have to nest your query twice.
For example, to paginate the query
select first_name from some_table order by first_name
you need to nest it like this
select first_name from
(select rownum as rn, first_name from
(select first_name from some_table order by first_name)
) where rn > 100 and rn <= 200
The reason for this is that rownum is determined after the where clause and before the order by clause. To see what I mean, you can query
select rownum,first_name from some_table order by first_name
and you might get
4 Diane
2 Norm
3 Sam
1 Woody
That's because oracle evaluates the where clause (none in this case), then assigns rownums, then sorts the results by first_name. You have to nest the query so it uses the rownum assigned after the rows have been sorted.
The second nesting has to do with how rownum is treated in a where condition. Basically, if you query "where rownum > 100" then you get no results. It's a chicken and egg thing where it can't return any rows until it finds rownum > 100, but since it's not returning any rows it never increments rownum, so it never counts to 100. Ugh. The second level of nesting solves this. Note it must alias the rownum column at this point.
Lastly, your order by clause must make the query deterministic. For example, if you have John Doe and John Smith, and you order by first name only, then the two can switch places from one execution of the query to the next.
There are articles here http://www.oracle.com/technology/oramag/oracle/06-sep/o56asktom.html
and here http://www.oracle.com/technology/oramag/oracle/07-jan/o17asktom.html. Now that I see how long my post is, I probably should have just posted those links...
Unfortunately, the methods for restricting the range of rows returned by a query vary from one DBMS to another: Oracle uses ROWNUM (see ocdecio's answer), but ROWNUM won't work in SQL Server.
Perhaps you can encapsulate these differences with a function that takes a given SQL statement and first and last row numbers and generates the appropriate paginatd SQL for the target DBMS - i.e. something like:
sql = paginated ('select empno, ename from emp where job = ?', 101, 150)
which would return
'select * from (select v.*, ROWNUM rn from ('
+ theSql
+ ') v where rownum < 150) where rn >= 101'
for Oracle and something else for SQL Server.
However, note that the Oracle solution is adding a new column RN to the results that you'll need to deal with.
I believe that both have a ROWNUM analytic Function. Use that and you'll be identical.
In Oracle it is here
ROW_NUMBER
Yep, just verified that ROW_NUMBER is the same function in both.
"Because...data can be change from other sessions."
What do you want to happen for this ?
For example, user gets the 'latest' ten rows at 10:30.
At 10:31, 3 new rows are added (so those ten being view by the user are no longer the latest).
At 10:32, the user requests then 'next' ten entries.
Do you want that new set to include those three that have been bumped from 8/9/10 down to 11/12/13 ?
If not, in Oracle you can select the data as it was at 10:30
SELECT * FROM table_1 as of timestamp (timestamp '2009-01-29 10:30:00');
You still need the row_number logic, eg
select * from
(SELECT a.*, row_number() over (order by hire_date) rn
FROM hr.employees as of timestamp (timestamp '2009-01-29 10:30:00') a)
where rn between 10 and 19
select *
from ( select /*+ FIRST_ROWS(n) */ a.*,
ROWNUM rnum
from ( your_query_goes_here,
with order by ) a
where ROWNUM <=
:MAX_ROW_TO_FETCH )
where rnum >= :MIN_ROW_TO_FETCH;
Step 1: your query with order by
Step 2: select a.*, ROWNUM rnum from ()a where ROWNUM <=:MAX_ROW_TO_FETCH
Step 3: select * from ( ) where rnum >= :MIN_ROW_TO_FETCH;
put 1 in 2 and 2 in 3
If the expected data set is huge, I'd recommend to create a temp table, a view or a snapshot (materialized view) to store the query results + a row number retrieved either using ROWNUM or ROW_NUMBER analytic function. After that you can simply query this temp storage using row number ranges.
Basically, you need to separate the actual data fetch from the paging.
There is no uniform way to ensure paging across various RDBMS products. Oracle gives you rownum which you can use in where clause like:
where rownum < 1000
SQL Server gives you row_id( ) function which can be used similar to Oracle's rownum. However, row_id( ) isn't available before SQL Server 2005.