Could you tell me please if it is possible to identify missing indexes for a select query using SQLite database?
Or is there any tool that can help?
Thank you!
Use EXPLAIN QUERY PLAN command to identify missing index for given SQL query. For example, the following result indicates you may need an index for a in table t1.
sqlite> EXPLAIN QUERY PLAN SELECT a, b FROM t1 WHERE a=1;
SCAN TABLE t1
If you have a lot of SQL queries and want to quickly identify missing index, I wrote a tool which helps analyze many SQL queries and saves you much time in the repeating process.
Using the sqlite3 command line tool, first enter
.expert
And then run your query as normal.
Related
We need to use GenerateTableFetch to fetch huge data from teradata using nifi. But since Teradata is not present as a database type it generate Limit keyword. I am able to replace it with Sample keyword. But sample everytime give random value so how can i use Nifi with Teradata for huge table?
Maybe try the "MS SQL 2008" adapter, it generates a TOP statement as well as a ROW_NUMBER() OVER clause. If that doesn't work, we'd need a TeradataDatabaseAdapter implementation, please feel free to file an improvement Jira as needed.
My system needs to validate if an oracle query contains order by. I thought I would do with regex but I wanted to know if oracle does not have a ready solution.
I tried to execute the with oracle explain plan but in some queries the order by does not appear in the plan.
Use regex:
.*order by.*
Some queries that don't have an order by, such as union, still internally perform sorts, so you can't tell by looking explain plan if an order by has been used.
I've never dealt with Teradata database before, I need to find out the data types for a table in Teradata I tried the below queries but none of them worked
describe table tablename; show create table tablename;help table tablename;
When I did show table I realized that it is a view and I tried
show view view name;
help view view name;
none of the above queries gave me the datatypes for the view I'm looking to find out. i googled around and tried my findings none of them worked.
Please help me with the query to find out the data types in teradata.
Thanks in advance
HELP COLUMN mytable.*; resolves views and returns the actual datatypes.
The description of the two character ColumnType can be found in the Data Dictionary manual
The stuff people have already said is great if you need the whole table. However, if you just need 1 specific field and want the result to be readable (without having to dig around in the data dictionary manual), sometimes I find it simpler to just do something like:
Select Distinct TYPE(Fieldname)
from mytable
For many reasons, this isn't the solution you want to use every time but I think it is worth adding to what people have already said.
I am using sqlite3 (maybe sqlite4 in the future) and I need something like dynamic tables.
I have many tables with the same format: values_2012_12_27, values_2012_12_28, ... (number of tables is dynamic) and I want to select dynamically the table that receives some data.
I am using _sqlite3_prepare with INSERT INTO ? VALUES(?,?,?). Ofcourse this fails to compile (syntax error near ?). There is a nice and simple way to do this in sqlite ?
Thanks
Using SQL parameters is not possible for identifiers such as table or column names.
If you don't want to keep so many prepared statements around, just prepare them on the fly whenever you need one.
If your database were properly normalized, you would have a single big values table with an extra date column.
This organization is usually to be preferred, unless you have measured both and found that the better performance (if it actually exists) outweighs the overhead of managing multiple tables.
I have a very simple query:
SELECT count(id), min(id), max(id), sum(size), sum(frames), sum(catalog_size + file_size)
FROM table1
table1 holds around 3000 to 4000 records.
My problem is that it takes around 20 seconds to this query to run. And since it is called more than once, the delay is pretty obvious to the customer.
Is it normal to this query to take 20 seconds? Is there any way to improve the run time?
If I run this same query from SQLite Manager it takes milliseconds to execute. The delay only occurs if the query is called from our software. EXPLAIN and EXPLAIN QUERY PLAN didn't help much. We use SQLite 3.7.3 version and Windows XPe.
Any thoughts how to troubleshoot this issue or improve the performance of the query?
All the sums require that every single record in the table must be read.
If the table contains more columns than those shown above, then the data read from the disk contains both useful and useless values (especially if you have big blobs). In that case, you can try to reduce the data needed to be read for this query by creating a covering index over exactly those columns needed for this query.
In SQLite versions before 3.7.15, you need to add an ORDER BY for the first index field to force SQLite to use that index, but this doesn't work for all queries. (For your query, try updating to this beta, or wait for 3.7.15.)