I'm having problems finding examples of sqlite3 queries. The diagrams in the documentation are useless. I want to say...
delete from food_post where ip_address=190.17.107.106;
I keep getting a syntax error, though. :/
Possibly because of multiple periods in your number. Instead try
delete from food_post where ip_address="190.17.107.106";
Related
Is there a way to search for a keyword across all columns of all tables in Azure Data Explorer? I know "* has" syntax works for searching in all columns in a table but if I want to search for a keyword across all tables, how do I do it?
from an efficiency standpoint, it's better, whenever possible, to scope your query only to the specific table(s) which is (are) relevant to your use case.
that said, you may want to look at the find operator: https://learn.microsoft.com/en-us/azure/kusto/query/findoperator
You can try below option:
search in (*) "NPA*" or "CSA*"
i'm using SQLite and trying to use the Lead function but I keep getting an error message (pasted below) from my DB Browser. Does anyone know what the issue is? And also, could you please talk me through your thought process of how you would debug the error below? Thank you so much in advance
MY CODE
SELECT Day.Close, Day.Open, Day.Close - Day.Open AS Movement1, LEAD Day.Close OVER (ORDER BY Day.High) AS Movement2 FROM ES_SourceNT_Day_ADX14 AS Day;
RESPONSE FROM DB BROWSER
near ".": syntax error: SELECT Day.Close, Day.Open, Day.Close - Day.Open AS Movement1, LEAD Day.
It seems like you forgot the closing quotes at the end of "N/A, and you can explicitly specifying the table name (or even specifying a table alias to begin with) is superfluous if you only have one table, so your query can be written as
SELECT Close, Open, Close - Open AS Movement1, LEAD (Close, 1, "N/A") OVER (ORDER BY High) AS Movement2 FROM ES_SourceNT_Day_ADX14;
But this is not the problem. In fact you have no problem if you are using SQLite version 3.25.0 or newer, but unfortunately earlier versions had no support for window functions.
See the changelist.
As for my thought process, at first I just tried to simplify your query, removing everything that seemed to be correct, to find a minimal bug repro, the shortest possible code that still produces the error. I went as far as to shorten it to
SELECT lead(High) OVER (ORDER BY High) FROM ES_SourceNT_Day_ADX14;
then
SELECT row_number() OVER (ORDER BY High) FROM ES_SourceNT_Day_ADX14;
Still didn't work, and I didn't know why, but I was starting to get suspicious.
I looked up the official documentation, and tried to run the simplest example, but to no avail. That's when I figured it out. SQLite is famously well tested, if such a huge subset of features doesn't work at all, the most likely explanation is that it is not supposed to work, at least not in this version.
Reading the changelist confirmed my theory.
I am using Python with sqlite3.
Is there an advantage to using FTS3 or FTS4 if I only want to search for words in one column, or I could just use LIKE "%word%"?
While yes, you could handle the simplest of cases with LIKE '%word%', FTS allows user queries like clown NOT circus (matches rows talking about clowns but not circuses). It handles stemming (well, in English) so that break would match against breaks but not breakdance. It also builds indexes in a different way so that searching is much faster for this sort of query, and can return not just where the match happened but also a snippet of the matched text.
Finally, all the parsing of those potentially-complex user queries is done for you; that's code you don't have to write at all.
I need to write single lines to a file placed on a file server. I am considering utilizing SQLite to ensure that the writing of the line was successful and not just partially completed. However, as insert performance is really essential. My question is, what is the exact process (as it read this, write that, read this and so on) that SQLite goes through when it inserts a row to a table. The table does not have any indexes, nor primary keys, constraints or anything.
This is the most common bottleneck in my experience:
http://www.sqlite.org/faq.html#q19
Except for that, SQLite is really fast. :)
You should use transactions and thus try to avoid fsync()-ing on every INSERT. Take a look here for some benchmarks.
Also, be sure to properly set the two important pragmas:
synchronous (NORMAL)
journal_mode (WAL)
you can use explain for details what happens when you execute a statement: http://www.sqlite.org/lang_explain.html
In looking up how to perform an equivalent to SELECT TOP 5 with LINQ-to-SQL, all the answers I've seen suggest using .Take(), like so:
var myObject = (
from myObjects in repository.GetAllMyObjects()
select myObject)
.Take(10);
I don't yet understand most of how LINQ works behind-the-scenes but to my understanding of C-like languages this would resolve by first assigning a temporary array containing ALL records, then copying the first 10 elements in the array to var. Not such a problem if you're working on a small dataset or without any performance constraints but it seems horribly inefficient to me if you're, for example, selecting the most recent 5 log entries from a table which can contain millions of records.
Is my understanding of how this works wrong? If so, could someone explain what actually happens? Otherwise, what (if any) better (ie more efficient) way is there of only selecting x records through LINQ-to-SQL?
[edit]
I have the hypothetical myObject class sending LINQ-to-SQL output to the debug output as per the suggestion in the accepted answer. I ended up using the DebuggerWriter from here: http://www.u2u.info/Blogs/Kris/Lists/Posts/Post.aspx?ID=11
Your assumption is incorrect. With Linq to SQL, it evaluates to an Expression<Func<...>> which can be evaluated and the proper SQL generated. You do not need to worry about it loading all the records.
Also, see this following question. You can attach a stream to your DataContext and see the SQL generated.
How to get the TSQL Query from LINQ DataContext.SubmitChanges()
LINQ uses deferred execution, and, for LINQ-to-SQL, expression trees.
No query will be executed until you enumerate the result of the Take call, so you don't need to worry about anything.
I just went through this last week! I opened the SQL profiler on my dev data base and stepped through the code. It was very interesting to see the generated SQL for the various queries. I recommend you do the same. It may not be an exact answer to your question but it was certainly enlightening to see how your various components generate entirely different SQL statements depending on the contents of the call.
I believe the "deferred query resolution" or something (?) reading on MSDN would be enlightening as well.