I have a user list table on my listing page. The data needs to be paged, so how can I make SQL page the data for me (ie. pull the data in sets of 10 records from the table)?
Informix has clauses analogous to, but different from, LIMIT and OFFSET:
SELECT SKIP n LIMIT m ...
You can use FIRST in place of LIMIT.
See the IDS 11.70 InfoCenter, or similar locations for earlier versions of IDS.
Now that you pointed out that you are using Informix, the LIMIT clause will not work. Are you able to instead place your selection into an array and call for the desired data from the array?
Related
I have read that in Postgres setting LIMIT NULL will effectively not limit the results of the SELECT. However in BigQuery when I set LIMIT NULL based on a condition I see Syntax error: Unexpected keyword NULL.
I'd like to figure out a way to limit or not based on a condition (could be an argument passed into a procedure, or a parameter passed in by a query job, anything I can write a CASE or IF statement for). The mechanism for setting the condition shouldn't matter, what I'm looking for is whether there is a way to syntactically indicate a value for LIMIT, that will not limit, in a valid way to BigQuery.
The LIMIT clause works differently within BigQuery. It specifies the maximum number of depression inputs in the result. The LIMIT n must be a constant INT64.
Using the LIMIT clause, you can overcome the limitation on cache result size:
Using filters to limit the result set.
Using a LIMIT clause to reduce the result set, especially if you are
using an ORDER BY clause.
You can see this example:
SELECT
title
FROM
`my-project.mydataset.mytable`
ORDER BY
title DESC
LIMIT
100
This will only return 100 rows.
The best practice is to use it if you are sorting a very large number of values. You can see this document with examples.
If you want to return all rows from a table, you need to omit the LIMIT clause.
SELECT
title
FROM
`my-project.mydataset.mytable`
ORDER BY
title DESC
This example will return all the rows from a table. It is not recommended to omit LIMIT if your tables are too large, as it will consume a lot of resources.
One solution to optimize resources is to use cluster tables. This will save costs and querying times. You can see this document with a detailed explanation of how it works.
You can write a stored procedure that dynamically creates a query based on input parameters. Once your sql query is ready, you can use execute immediate to run that. In this way, you can control what value should be provided to the limit clause of your query.
https://cloud.google.com/bigquery/docs/reference/standard-sql/scripting#execute_immediate
Hope this answers your query.
Let's say I have the following 'items' table in my PostgreSQL database:
id
item
value
1
a
10
2
b
20
3
c
30
For some reason I can't control I need to run the following query:
select max(value) from items;
which will return 30 as the result.
At this point, I know that I can find the record that contains that value using simple select statements, etc. That's not the actual problem.
My real questions are:
Does PostgreSQL know (behind the scenes) what's is the ID of that
record, although the query shows only the max value of the column
'value'?
If yes, can I have access to that information and,
therefore, get the ID and other data from the found record?
I'm not allowed to create indexes and sequences, or change way the max value is retrieved. That's a given. I need to work from that point onward and find a solution (which I have, actually, from regular query work).
I'm just guessing that the database knows in which record that information (30) is and that I could have access to it.
I've been searching for an answer for a couple of hours but wasn't able to find anything.
What am I missing? Any ideas?
Note: postgres (PostgreSQL) 12.5 (Ubuntu 12.5-0ubuntu0.20.10.1)
You can simply extract the whole record that contains max(value) w/o bothering about Postgres internals like this:
select id, item, "value"
from items
order by "value" desc
limit 1;
I do not think that using undocumented "behind the scenes" ways is a good idea at all. The planner is smart enough to do exactly what you need w/o extra work.
Given a SELECT statement in Big Query and the Java SDK, what are my options to get the actual column names without fetching the data? I know I can execute the statement and then get the Schema via the TableResult. But is there a way to get the names without fetching data? We have a tool where we run arbitrary queries which are not known upfront and in my code I want to access the result columns by name.
Update: someone flagged this as duplicate of a 7 year old entry. I am however looking for a way to use the Java SDK alone to get the column names, not to do some magic with the query itself or query some metatable.
There are few options but the easiest is to add limit 0 to your query so for example:
SELECT * FROM projectId.datasetId.tableId limit 0
I have a client talking with server program(using sqlite3 as the storage) which needs to support paging. I am thinking about how to implement that. One approach:
1) user request page 1
a. execute query from sqlite3
b. return the first page range items to client
2) user request page N
a. execute query from sqlite3
b. return the N page range itmes to client
So in my approach every time user requests data I will re issue the query and get the specified elements, which seems waste of time...(comparing with caching all the items one time and just give the portion user asks, but this approach is more complex, as I need to timeout the cache - user is using browser I don't know when the user is loggout and the cache is useless)
Any better ideas?
Maybe you could use the LIMIT… OFFET… capability of SQLite.
Taken from the select syntax documentation:
Instead of a separate OFFSET clause, the LIMIT clause may specify two scalar expressions separated by a comma. In this case, the first expression is used as the OFFSET expression and the second as the LIMIT expression. This is counter-intuitive, as when using the OFFSET clause the second of the two expressions is the OFFSET and the first the LIMIT. This is intentional - it maximizes compatibility with other SQL database systems.
What's the equivalent of mysql Limit in ms access. TOP is not sufficient since I'm going to use it for pagination.
Thanks
There isn't one. Your best bet is to add an ID column as a primary key (if you don't already have one) and chunk output by looping through:
SELECT * FROM table
WHERE id >= offset AND id <= offset + chunk_size - 1
until you get all the rows.
Curiously, there are a few references in Microsoft documentation to a LIMIT TO nn ROWS syntax for the Access Database Engine:
ACC2002: Setting ANSI 92 Compatibility in a Database Does Not Allow DISTINCT Keyword in Aggregate Functions
About ANSI SQL query mode (MDB)
However, actual testing seems to confirm that this syntax has never existed in a release version of the Access Database Engine. Perhaps this is one of those features that the SQL Server team wanted to put into Jet 4.0 but were ordered to rollback by the Windows team? Whatever, it seem we must simply put it down to a bad documentation error that Microsoft won't take the time to correct :(
If you need to do pagination on the server** side then I suggest you consider a more capable, modern SQL product with better documentation ;)
** conceptually, that is: the Access Database Engine is not a server DBMS.
Since it doesn't appear that you have any type of sequencial unique key number for these rows, you'll need to create a ranking column: How to Rank Records Within a Query
You need to determine how many rows at a time you will return N = (10, 25,100).
You need to keep track of what "page" the user is on and the values of the first and last rank.
Then when you make the call for the next page it is either the next N rows that are > or < the first and last ranks (depending if the users is going to the previous or next page.).
I'm sure there is a way to calculate the last page, first page, etc.
Only way to achive paging SQL similar to Limit statement by using TOP keywords is as follows:
First Step:
sql = "select top "&LESS_COUNT&" * from (SELECT top "&(PAGE_COUNT*getPage)&" * FROM (SELECT "&COLUMNS&" FROM "&TABLENAME&") AS TBL "&getWhere&getOrderby("asc")&") as TBL "&getOrderby("desc")
Second step:
sql = "SELECT TOP "&PAGE_COUNT&" * FROM (" & sql & ") as TBL "&getOrderby("asc")
To summarize; you should re-order and make the results upside down for 3 times.
port your project to PHP & MySQL. Better support for these type of actions and queries and much much better online documentation. As a 16 year veteran DB developer, I have grown to dispise MS Access and MS SQL with a passion unmatched by anything else. This is due exclusively to their lack of support and documentation.