I have three columns with datatype TIMESTAMP(6) and I wish to find out the minimum of the three timestamps. At any given time, there will be at least 1 non-null data point among the three columns.
I tried finding an alternative online but couldn't find anything related to timestamp comparison on this matter. There is a solution of using coalesce which works on data type date but not on timestamps.
I'm guessing you are asking about trying to use LEAST with timestamps? I don't know why Teradata hasn't done anything about that. For timestamps, I just cast them as varchar. Nulls make it uglier, because you have to coalesce them with something, depending on if you want null to be less than everything else or not.
select
least (
coalesce(null,'9999-12-31'), --if you want nulls to not be the least
cast(current_timestamp as varchar(32)),
cast(timestamp '2018-01-01 05:00:00' as varchar(32)))
In a real query, you'll end up combining coalesce and cast for every column you want to feed into the least function.
EDIT:
I should probably add that this works on YYYY-MM-DD dates, other formats may not sort correctly.
Related
as you can see, i try to list ads on my page by highest price. It didnt work. Checking it manually, and the result is weird. The price are not in order at all.
Your prices appear to be string values, which means they are going to be compared lexicographically, not numerically. In a lexicographic sort, two strings are compared by looking at the unicode values of their characters from left to right, like a dictionary. If you want a numerical sort, where the values are compared simply by their number values, you should be using a number type field instead of a string. This means you'll have to update each document to use numbers instead of strings where appropriate.
See also:
https://en.wikipedia.org/wiki/Lexicographical_order
https://www.quora.com/What-is-lexicographic-order
I see also you have what appears to be time values that don't much look like times. Look into using timestamp type fields instead, or numbers that will sort in chronological order.
I've found that sometimes comparing a timestamp on Google Sheets returned in a query differs from the original the query was based on.
At the online community I'm volunteering in, we use Google Forms to record volunteer hours. For our users to be able to verify their clock in/clock outs, we take the form responses with timestamps and filter them via a Query to only display those for one specific user:
=QUERY(A:F,"Select A,B,D where '"&J4&"'=F")
where J4 contains the username we are filtering for.
We calculate the row each stamp can be found in via a Match function where M2:M is the range containing the timestamp the query above returns and A2:A is the original timestamp.
=iferror(arrayformula(MATCH(M2:M,A2:A,0)+1),)
Now we found that sometimes, the MATCH failed even though we could verify that the timestamp in question existed. Some format wrangling later, we found the problem, illustrated for one example below:
The timestamp in question read 2/8/2018 4:12:47. Converted to a decimal, the value in column A turned into 43139.1755413195, while the very same time stamp in the query result read 43139.1755413194. The very last decimal, invisible unless you change the format to number and look at the formula line at the top of the sheet, has changed.
We have several different time stamps where the last decimal in the query result differs from the original the query is based on. Whether the last decimal in the query was one higher or lower than the original was inconsistent.
For our sheet, we now implemented a workaround of truncating the number earlier. However, that seems very inelegant. Is there a more elegant solution or a way to prevent (what we assume to be) rounding errors like this from happening? My search of google and the forums has not turned up anything like it, though I'm having trouble phrasing it in a way that gives me relevant hits.
How do I compare dates in SQLite database which are stored in DD-MMM-YYYY format e.g. 10-OCT-2017?
I want to compare dates and select rows of particular date and adjacent dates.
Short answer:
Painfully. You must convert the datestring, particularly the character month, into a numeric value, then you can compare the date values.
... Or more easily, by storing your dates using a format like “2018-01-01” which can be natively compared within the SQL via SQLite date functions.
Longer Answer
This page shows all the SQLite SQL date-time functions available. None of them produce or manipulate character month values. So your options are:
1) Select a group of records via SQL into a dataset; and then use your programming language to convert the date values in the dataset to a format whose values are comparable; then compare them.
This would have poor performance for anything except very small data queries, but would probably be reasonably simple to implement, and have no data conversion necessary. (To specifically answer the question you asked, this is the best solution for an app selecting few and small datasets.)
2) Create a SQLite function to do the date format conversion. To do that, you use SQLite's C API. See more how-to discussion here.
I haven't done this myself, and I wouldn’t recommend this route just due to the learning curve, but also due to the type & purpose of SQLite and its capabilities. (To specifically answer the question you asked, this is the best solution for not few and not small datasets.)
3) (This option does not answer your specific question) Convert your stored date values to a natively SQL comparable format. Like: “2018-01-01”. Then you can use the SQLite date-time functions for adjacent date comparisons.
Sample:
select mySQLTableDate, myOtherSQLTableDate
date(mySQLTableDate,'+1 day'), -- YYYY-DD-MM stored format
date(strftime('%Y-%m-%d', mySQLTableDate),'+1 day') -- many stored formats
from mySQLTable
where select mySQLTableDate = date(myOtherSQLTableDate,'+1 day')
Answering your question in terms of the goal rather than the specific question :) , my recommendation is to Use This Solution, especially if you are scanning a lot of data. See more about SQLite Date types here, but for dates with no time, I just store them as the string “2018-01-01”. I’m working with .js, and this is very simple to convert to/from a .js Date object.
Problem
Can't create a table with an index column that references multiple rows in a table. Picture example below of what I'm trying to create.
Overview
Imagine an (SQLite) table will hold stock dividend payments. The index column is set to the ticker symbols. However, each ticker symbol refers to multiple records, which are organized by a time stamp. The documentation on SQLite and about 15 other tutorials all seem to focus on indexing where there is always a 1:1 relationship between an index and a record. I would like to create an index with a 1:many relationship.
The lookup would find the appropriate stock by symbol, and then (probably) a secondary index on the dates in the first column. But I cannot find any examples where others have tried to set up this structure. Makes me think maybe I don't have the right approach, or this is just a special case.
I don't think your problem is actually a problem. Putting an index on a column doesn't mean it has to contain unique values. It's perfectly reasonable for values in an indexed column to repeat. Of course there are diminishing returns. E.g. If you have a million rows and only five different values in a column, an index on that column isn't really going to do much for you.
A good rule of thumb is to start with an index on the column(s) you're using in your where clause. Then run the queries and see if you're getting satisfactory performance.
I have values in a SQLite table* that contain a number of strings, of different lengths, joined by periods, something like this:
SomeApp.SomeNameSpace.InterestingString.NotInteresting
SomeApp.OtherNameSpace.WantThisOne.ReallyQuiteDull
SomeApp.OtherNameSpace.WantThisOne.AlsoDull
SomeApp.DifferentNameSpace.AlwaysWorthALook.LittleValue
I'd like to extract (in this case) the third period-delimited substring so I could write something like
SELECT interesting_string, COUNT(*)
FROM ( SELECT third_part_of_period_delimited_string(name) interesting_string )
GROUP BY interesting_string;
Obviously I can do this any number of ways programmatically; I'm wondering if there's any way to achieve this in a SQLite SELECT query?
* It's a SharpDevelop Profiler database, if anyone's curious
No.
You can, as you mention, work with the strings after you have selected them from the database. Or you can split them up into separate columns when they are stored.
If you do not have access to the code that is storing the data, you might want to consider reading the data in its entirety, splitting the strings and storing the split out tokens in separate columns in a new table. If the data is not too large, you might look at storing this table in a new memory database to give excellent performance.
Whether this is worthwhile depends on whether one pass to split the data strings can be made use of many times. If the data is constantly changing, then this scheme would probably not work well.