How can we use variable as column name ?
In my table days (MONDAY,TUESDAY..) are column names.
I want to get the DAY dynamically and use AS COLUMN NAME in my query.
My query :
SELECT EMP FROM SCHEDULE WHERE "DAY"(Dynamically I want) =1;
You simply can't use variables to change the actual text of the queries. variables can be used just in place of literal values (dates, strings, times, numbers) but they can't change the text of the actual command.
The technical reason is that (oversimplyfying the things) oracle FIRST parses the text, establishes an execution plan and only after this considers the values of the variables. more or less you can think (this is just an analogy, of course, it is not really the same thing!) that oracle "compiles" the queries like an C++ compiler compiles the source code of a function: it is not possible to pass a c++ procedure a variable that modifies the text of the procedure itself.
what you have to do is to rethink your approach taking in consideration what I just said:
SELECT EMP FROM SCHEDULE
WHERE
(case :DAY_I_WANT
WHEN 'MONDAY' then -- 'MONDAY' is the string value of the variable :DAY_I_WANT
monday -- monday, here is the column whose value I want CASE to return
WHEN 'TUESDAY' then tuesday
...
...
WHEN 'SUNDAY' then sunday
end) = 1
keep in mind that this solution will not take advantage on any index on the MONDAY..SUNDAY columns. the best approach would be to create a different data structure where you have a separate row for each day and a proper dayofweek column. If you do this, you will be able able to write:
select EMP from schedule
where schedule.DAY = :DAY_I_WANT
and it will allow you to create an index on the DAY column, speeding up searches.
Having a separate column for each day equals to be looking for troubles.
Related
There are records in table for particular date. But when I query with that value, I am unable to filter the records.
select * from TBL_IPCOLO_BILLING_MST
where LAST_UPDATED_DATE = '03-09-21';
The dates are in dd-mm-yy format.
To the answer by Valeriia Sharak, I would just add a few things since your question is tagged Oracle. I was going to add this as a comment to her answer, but it's too long.
First, it is bad practice to compare dates to strings. Your query, for example, would not even execute for me -- it would end with ORA-01843: not a valid month. That is because Oracle must do an implicit type conversion to convert your string "03-09-21" to a date and it uses the current NLS_DATE_FORMAT setting to do that (which in my system happens to be DD-MON-YYYY).
Second, as was pointed out, your comparison is probably not matching rows due LAST_UPDATED_DATE having hours, minutes, and seconds. But a more performant solution for that might be:
...
WHERE last_update_date >= TO_DATE('03-09-21','DD-MM-YY')
AND last_update_date < TO_DATE('04-09-21','DD-MM-YY')
This makes the comparison without wrapping last_update_date in a TRUNC() function. This could perform better in either of the following circumstances:
If there is an index on last_update_date that would be useful in your query
If the table with last_update_date is large and is being joined to other tables (because it makes it easier for Oracle to estimate the number of rows from your table that are inputs to the join).
Your column might contain hours and seconds, but they can be hidden.
So when you filter on the date, oracle implicitly adds time to the date. So basically you are filtering on '03-09-21 00:00:00'
Try to trunc your column:
select * from TBL_IPCOLO_BILLING_MST
where trunc(LAST_UPDATED_DATE) = '03-09-21';
Hope, I understood your question correctly.
Oracle docs
Have a query regarding this - have a table update where I have to backfill for over a years worth of data, and due to the code I have to update by day (which takes 4-5 mins per day), does anyone know how I can do this more effectively by setting a list of dates so I can do this in the background.
So for example if I set a variable called :reqdate which is the date field and I have a list of dates from a query (e.g. 01/01/20, 02/01/20... 04/04/20) is there something I can do to get sql to run this repeatedly eg :regdate=01/01/20, then when thats done it automatically does 02/01/20 and so on
Thanks
If I understood you correctly, the easiest way is to use merge clause like:
merge into dest_table t
using (
select date'2020-01-01'+N as dt
from xmltable('0 to 10' columns N int path '.')
) dates
on (t.date_col = dates.dt)
whem matched then update
set ...
Though I think you need to redesign your update to simple update like
update (select ... from) t
set ...
where t.dt between date'2020-01-01' and date'2020-01-20'
New to SQL. Pardon me if this question is a basic one. Is there a way for me to do this below
SELECT COLUMN1 as CUSTOM_NAME, <wildcard for remaining columns as is> from TABLE;
I only want COLUMN1 appear once in the final result
There is no way to make that kind of dynamic SELECT list with regular SQL*.
This is a good thing. Programming gets more difficult the more dynamic it is. Even the simple * syntax, while useful in many contexts, causes problems in production code. The Oracle SQL grammar is already more complicated than most traditional programming languages, adding a little meta language to describe what the queries return could be a nightmare.
*Well, you could create something using Oracle data cartridge, or DBMS_XMLGEN, or a trick with the PIVOT clause. But each of those solutions would be incredibly complicated and certainly not as simple as just typing the columns.
This is about as close as you will get.
It is very handy for putting the important columns up front,
while being able to scroll to the others if needed. COLUMN1 will end up being there twice.
SELECT COLUMN1 as CUSTOM_NAME,
aliasName.*
FROM TABLE aliasName;
In case you have many columns it might be worth to generate a full column list automatically instead of relying on the * selector.
So a two step approach would be to generate the column list with custom first N columns and unspecified order of the other columns, then use this generated list in your actual select statement.
-- select comma separated column names from table with the first columns being in specified order
select
LISTAGG(column_name, ', ') WITHIN GROUP (
ORDER BY decode(column_name,
'FIRST_COLUMN_NAME', 1,
'SECOND_COLUMN_NAME', 2) asc) "Columns"
from user_tab_columns
where table_name = 'TABLE_NAME';
Replace TABLE_NAME, FIRST_COLUMN_NAME and SECOND_COLUMN_NAME by your actual names, adjust the list of explicit columns as needed.
Then execute the query and use the result, which should look like
FIRST_COLUMN_NAME, SECOND_COLUMN_NAME, OTHER_COLUMN_NAMES
Ofcourse this is overhead for 5-ish columns, but if you ever run into a company database with 3 digit number of columns, this can be interesting.
In Oracle, while trying to concatenate two columns of both Number type and then trying to take MAX of it, I am having a question.
i.e column A column B of Number data type,
Select MAX(A||B) from table
Table data
A B
20150501 95906
20150501 161938
when I’m running the query Select MAX(A||B) from table
O/P - 2015050195906
Ideally 20150501161938 should be the output????
I am trying to format column B like TO_CHAR(B,'FM000000') and execute i'm getting the expected output.
Select MAX(A || TO_CHAR(B,'FM000000')) FROM table
O/P - 2015011161938
Why is 2015050195906 is considered as MAX in first case.
Presumably, column A is a date and column B is a time.
If that's true, treat them as such:
select max(to_date(to_char(a)||to_char(b,'FM000000'),'YYYYMMDDHH24MISS')) from your_table;
That will add a leading space for the time component (if necessary) then concatenate the columns into a string, which is then passed to the to_date function, and then the max function will treat as a DATE datatype, which is presumably what you want.
PS: The real solution here, is to fix your data model. Don't store dates and times as numbers. In addition to sorting issues like this, the optimizer can get confused. (If you store a date as a number, how can the optimizer know that '20141231' will immediately be followed by '20150101'?)
You should convert to number;
select MAX(TO_NUMBER(A||B)) from table
Concatenation will result in a character/text output. As such, it sorts alphabetically, so 9 appears after 16.
In the second case, you are specifiying a format to pad the number to six digits. That works well, because 095906 will now appear before 161938.
I have two tables for time dimension
date (unique row for each day)
time of the day (unique row for each minute in a day)
Given this schema what would a query look like if one wants to retrieve facts for last X hours where X can be any number greater than 0.
Things start to be become tricky when the start time and end time happen to be in two different days of the year.
EDIT: My Fact table does not have a time stamp column
Fact tables do have (and should have) original timestamp in order to avoid weird by-time queries which happen over the boundary of a day. Weird means having some type of complicated date-time function in the WHERE clause.
In most DWs these type of queries are very rare, but you seem to be streaming data into your DW and using it for reporting at the same time.
So I would suggest:
Introduce the full timestamp in the fact table.
For the old records, re-create the timestamp from the Date and Time keys.
DW queries are all about not having any functions in the WHERE clause, or if a function has to be used, make sure it is SARGABLE.
You would probably be better served by converting the Start Date and End Date columns to TIMESTAMP and populating them.
Slicing the table would require taking the appropriate interval BETWEEN Start Date AND End Date. In Oracle the interval would be something along the lines of SYSDATE - (4/24) or SYSDATE - NUMTODSINTERVAL(4, 'HOUR')
This could also be rewritten as:
Start Date <= (SYSDATE - (4/24)) AND End Date >= (SYSDATE - (4/24))
It seems to me that given the current schema you have, that you will need to retrieve the appropriate time IDs from the time dimension table which meet your search criteria, and then search for matching rows in the fact table. Depending on the granularity of your time dimension, you might want to check the performance of doing either (SQL Server examples):
A subselect:
SELECT X FROM FOO WHERE TIMEID IN (SELECT ID FROM DIMTIME WHERE HOUR >= DATEPART(HOUR, CURRENT_TIMESTAMP()) AND DATEID IN (SELECT ID FROM DIMDATE WHERE DATE = GETDATE())
An inner join:
SELECT X FROM FOO INNER JOIN DIMTIME ON TIMEID = DIMTIME.ID WHERE HOUR >= DATEPART(HOUR, CURRENT_TIMESTAMP()) INNER JOIN DIMDATE ON DATEID = DIMDATE.ID WHERE DATE = GETDATE()
Neither of these are truly attractive options.
Have you considered that you may be querying against a cube that is intended for roll-up analysis and not necessarily for "last X" analysis?
If this is not a "roll-up" cube, I would agree with the other posters in that you should re-stamp your fact tables with better keys, and if you do in fact intend to search off of hour frequently, you should probably include that in the fact table as well, as any other attempt will probably make the query non-sargable (see What makes a SQL statement sargable?).
Microsoft recommends at http://msdn.microsoft.com/en-us/library/aa902672%28v=sql.80%29.aspx that:
In contrast to surrogate keys used in other dimension tables, date and time dimension keys should be "smart." A suggested key for a date dimension is of the form "yyyymmdd". This format is easy for users to remember and incorporate into queries. It is also a recommended surrogate key format for fact tables that are partitioned into multiple tables by date.
Best luck!