I need to search rows entered on a specific date.
However the datatype of column I need to search on is datetime, and the datatype of argument is Date.
I can use the the query like
Select result
from table
where
convert(date, Mycolumn) = #selectedDate
but this would affect the SARGability of the query and will not use indexes created on mycolumn.
I was trying to use the following query:
Select result
from table
where
Mycolumn
BETWEEN #selectedDate AND Dateadd(s, -1, Dateadd(D, 1, #selectedDate))
However this does not work since the #selectedDate is Date type and a second can't be added or removed.
Can someone help me with a working query?
Thanks.
It is my understanding that using:
convert(date, Mycolumn) = #selectedDate
is SARGable. It will use the index on Mycolumn (if one exists). This can easily be confirmed by using the execution plan.
Select result
from table
where
Mycolumn >= #selectedDate
AND Mycolumn < Dateadd(D, 1, #selectedDate)
If you need to do these searches a lot, you could add a computed, persisted column that does the conversion to DATE, put an index on it and then search on that column
ALTER TABLE dbo.YourTable
ADD DateOnly AS CAST(MyColumn AS DATE) PERSISTED
Since it's persisted, it's (re-)calculated only when the MyColumn value changes, e.g. it's not a "hidden" call to a stored function. Since it's persisted, it can also be indexed and used just like any other regular column:
CREATE NONCLUSTERED INDEX IX01_YourTable_DateOnly ON dbo.YourTable(DateOnly)
and then do:
SELECT result FROM dbo.YourTable WHERE DateOnly = #SelectedDate
Since that additional info is stored in the table, you'll be using a bit more storage - so you're doing the classic "space vs. speed" trade-off; you need a bit more space, but you get more speed out of it.
Related
I am trying to replace all of the NULL values to 0 in a column of a big table in HIVE.
However, every time I try to implement some code I end up generating a new column to the table. The column I am trying to change/modify still exists and still has the NULL values but the new column that is automatically generated (i.e. _c1) is what I want the column I am trying to modify, to look like.
I tried to run a COALESCE but that also ended up generating a new column. I also tried to implement a CASE WHEN, but the same results ensued.
Select *,
CASE WHEN columnname IS NULL THEN 0
ELSE columnname
END
from tablename;
Also tried
SELECT coalesce(columnname, CAST(0 AS BIGINT)) FROM tablename
I would just like to update the table with the other columns being as is but the column I want to modify still has its original name but instead of NULL values it has 0's that replaced them.
I don't want to generate a new column but modify an existing one.
How should I do that?
Use insert overwrite .. option.
insert overwrite table tablename
select c1,c2,...,coalesce(columnname,0) as columnname
from tablename
Note that you have to specify all the other column names required in select.
How can I use a column value as a column name. I've tried this:
SELECT TableX.(
SELECT OdTable.columnamecell
from OdTable
where 1 =1
AND OdTable.KeyValue = TableX.SomeValue
) as MyValue
,TableX.OtherValue as OtherValue
, TableX.SomeValue
from TableX
WHERE 1 = 1
Or to say it another way: Can I use a table column value as a column name for another query or sub-query?
To clarify: The table: OdTable has a column with values that are the column name in another table.
No, and Yes. You can't do this with "standard" SQL; all table and column names must be known, as literals, when the query is compiled; they can't be provided at runtime. What you want is called "dynamic SQL"; sometimes it is the only solution to a problem, but most of the time it is used when it is not necessary. It has several disadvantages (security risk, performance penalty, difficulty to maintain, ...)
I would like convert the column name to date.
for example the column name is today, i want to convert it dynamically to today's date like MM/DD/YYYY .
as of now the column name is "Today" i want it to be current date
You can't configure a column to change its name automagically. To reflect the current day or whatever else.
But, you can change the column name by using an alias when doing a query. In order to make the things the more transparent as possible, you might want to create a view. Here is an example:
-- Some table with a column named "TODAY"
CREATE TABLE T AS (SELECT LEVEL today FROM DUAL CONNECT BY LEVEL < 5);
-- Use PL/SQL to create a view on the given table
-- with a dynamic column name
DECLARE
today varchar(10) := TO_CHAR(SYSDATE,'DD/MM/YYYY');
query varchar(200) := 'CREATE OR REPLACE VIEW V'
|| ' AS SELECT today "' || today || '"'
|| ' FROM T';
BEGIN
execute immediate query;
END;
Then, to query the "table" with the right column name, you will simply need to query V instead of T:
SELECT * FROM V;
12/12/2014
1
2
3
4
If you recreate your view daily, say by calling the above PL/SQL code from a job, you will see each day a view with the current date as the column name. But, as the underlying table is left unchanged, you will still be able to query it using the canonical name today. Which is important for example if you need to perform join on that table.
That being said, I'm not sure I will push toward such a solution. Use at your own risks!
If you want the column name heading to appear as something different than what the column name is defined in the table, you simply use the as "DisplayColumnName" clause for that column:
select user_name, today as "12/12/2014" from some_table;
But you would need to programatically generate the SQL statement for that to work. What coding environment you are using would dictate how to dynamically create a select statement.
I have a table in oracle db which has a unique index composed of two columns (id and valid_from). The column valid_from is of type timestamps with time zone.
When I query the SYS.USER_IND_COLUMNS to see which columns my table is using as unique index, I can not see the name of the valid_from column but instead I see smth like SYS_NC00027$.
Is there any possibility that I can display the name valid_from rather than SYS_NC00027$. ?
Apparently Oracle creates a function based index for timestamp with time zone columns.
The definition of them can be found in the view ALL_IND_EXPRESSIONS
Something like this should get you started:
select ic.index_name,
ic.column_name,
ie.column_expression
from all_ind_columns ic
left join all_ind_expressions ie
on ie.index_owner = ic.index_owner
and ie.index_name = ic.index_name
and ie.column_position = ic.column_position
where ic.table_name = 'FOO';
Unfortunately column_expression is a (deprecated) LONG column and cannot easily be used in a coalesce() or nvl() function.
Use the below to verify the col info.
select column_name,virtual_column,hidden_column,data_default from user_tab_cols where table_name='EMP';
I want to have a column in table which calculates the value depending on the other column in the same table.
For example,
I have "Validity" Table with Columns "DateManufactured", "DateExpires"
The Date Expires column must calculate value suppose adding 30 days for Datemanufactured.
How Can we do this in Visual Studio2010->DataSet Design-> DataTable Column-> Properties->Expression
See relevant Image here
What could be the possible expression for this in terms of SQL Server Expressions?
Please Suggest optimal Solution.
Thanks in advance.
I believe you are looking for DateAdd
SELECT DATEADD(day, 30, '15 Dec 1988')
select dateadd(day,30,getdate())
this will take the current date(getdate())
add 30 days to it.
I would suggest creating a stored procedure to insert your data into your table with parameters of the values that needs to be inserted. you can then do your calculation based on your date parameter. Example:
Create Procedure InsertValidity
(
#City varchar(20),
#Area varchar(20),
...
#DatePosted datetime,
...
#UserID
)
as
declare #DurationFrom datetime
set #DurationFrom = (select DATEADD(dd,30,#DatePosted)
insert into Validity (City, Area, ..., DatePosted, ... UserID)
values(#City, #Area, ..., #DatePosted,...#DurationFrom,...#UserID)
This should solve your problem. Just complete the script by replacing the ... with your other data then execute the stored procedure in your application.