I am trying to create a new generated column call memberstat which is a boolean that will hold just a 'True' or 'false' if the current date is greater than expiration date.
So far, whenever i create 'memberstat boolean generated always as (case when expiredate < current_date then '0' else '1' end) stored' this generates an ERROR: generation expression is not immutable.
Is there a way around this? sorry I am not that familiar with postgresql
As you have seen the function CURRENT_DATE cannot be used is a virtual column definition because it will change without the values in the row changing. A virtual column must be based only on the data in the same row.
The solution is to create a view using either your case statement or a simple comparison operator.
CREATE VIEW expired_or_not AS
SELECT
product_id,
product_name,
expiredate < current_date AS "expired"
FROM table_name;
which will return t or f.
Related
I have a table in Posgres that contains task start and task end dates. It's possible to generate a column in this tale as rate between (current day -start day) /(start day-end day) the column is the % of time elapse. I try in this way but does not work.
ALTER TABLE public.gantt_task
ADD COLUMN
percentage_progress
GENERATED ALWAYS AS (
(DATEDIFF("day",
CURRENT_DATE,public.gantt_Tasks.start_date)) / DATEDIFF("day", public.gantt_Tasks.end_date ,public.gantt_Tasks.start_date))
STORED
The manual says postgres only supports materialized (ie, stored) generated columns, which means the value is generated when the row is inserted or updated, which means it will use the insert/update date, not the CURRENT_DATE you want.
So, you need to create a view instead. This allows evaluating CURRENT_DATE at the date of the SELECT, not the INSERT/UPDATE, to generate columns.
CREATE VIEW foo AS SELECT *,
(CURRENT_DATE - public.gantt_Tasks.start_date)
/ (public.gantt_Tasks.end_date-public.gantt_Tasks.start_date)
AS percentage_progress
FROM public.gantt_task
Note DATEDIFF is mysql syntax not postgres, and division by zero is not allowed, so if start_date and end_date can be identical then you'll have to modify the expression conditions depending on what you want. Also your expression will go over 100% when CURRENT_DATE is later than end_date. Perhaps something like:
least( 1.0, (CURRENT_DATE-start_date)/greatest( 1, end_date-start_date)::FLOAT )
I won't write proper SQL code. But you might/should split it into two or three tasks:
Add new column that allows null (that should be default)
Update table
Add constrains (if required)
My table has end_date column as Date type
It will have an actual value, a default value or NULL value
If end date is populated for an employee, it will have actual date
Default date is 2000-01-01 in yyyy-MM-dd format which is populated
on 1st of every month
When a new employee joins in the middle, it has NULL value
I need to make a query which will return the difference in days if it has an actual end date or blank if NULL or default value is there.
Select GREATEST(0, DATE_PART('day', end_date::timestamp - CURRENT_DATE))
This is the best bet I could manage as of now. Any way of doing it without If-Else conditions?
Try to use this in your select-list:
NULLIF(end_date, '2000-01-01') - CURRENT_DATE
The NULLIF if will return NULL, iff both parameters are the same, and the first parameter otherwise. Subtraction with a NULL value (on any side of the operator) will yield NULL as well, thus this will give you a "blank" output if end_date is not set or is set to the default (if you desire some other special value, surround this "query" with a COALESCE and add your default-blank-value as its second parameter). Otherwise you get your desired difference.
I do not see, why there should be any need to cast to TIMESTAMP. This will make the subtration to return an INTERVAL, but you want an INTEGER and this is what you get by subtracting two DATEs.
I am trying to compare a particular date in my SQL query in ORACLE BUT it is returning a null value. But if I am using greater than or less then it is working fine. Please check it and revert me with your feedback..
SELECT *
FROM TICK
WHERE stock_id = 7108
AND TRUNC(TICK_date) = To_date('30/08/2013', 'dd/mm/yyyy')
Returning null value means that there is no record which tick_date column is equivalent to To_date('30/08/2013', 'dd/mm/yyyy') after being truncated. What is your problem? I don't get it.
In this data - there are multiple DATA_ID values associated with time-series data. I am trying to exclude all data from any DATA_ID values that return a NULL value for USE for any timestamp value.
In other words, I only want to return DATA_ID values (and their data) if they have complete (not any NULL) values for all timestamp values.
Sample query given below:
SELECT
My.Table.DATA_ID,
MY.Table.timestamp,
My.Table.USE
FROM
My.TABLE
WHERE timestamp BETWEEN '2012-06-01 00:00:00' AND '2012-06-02 23:59:59'
-- Something here that says exclude all data from DATA_ID(s)
-- with any missing USE data, i.e. USE=NULL
ORDER BY DATA_ID, timestamp
Assuming I understand your question correctly and you want to exclude whole batches of samples (determined by equal data_id and timestamp) that contain a null value.
SELECT
My.Table.DATA_ID,
MY.Table.timestamp,
My.Table.USE
FROM
My.TABLE o
WHERE timestamp BETWEEN '2012-06-01 00:00:00' AND '2012-06-02 23:59:59'
and not exists (select 1 from my_table i
where i.use is null
and i.data_id = o.data_id
and i.timestamp BETWEEN '2012-06-01 00:00:00' AND '2012-06-02 23:59:59')
ORDER BY DATA_ID, timestamp
The simple thing to do is something like this:
CREATE FUNCTION missing_info(MY.TABLE)
RETURNS BOOL
LANGUAGE SQL AS
$$ select $1.use is null -- chain conditions together with or.
-- no from clause needed. no where clause needed.
$$;
Then you can just add:
where (My.Table).missing_info is not true;
And as you need to change the logic as to what sorts of info is missing you can just change it in the function and everything still works.
This is the sort of encapsulation of derived information where ORDBMS's like PostgreSQL really shine.
Edit: Re-reading your example, it looks like what you are looking for is the IS NULL operator. However if you need to re-use some sort of logic, see the above example. NULL never "equals" NULL (because we can't say whether two unknown values are the same). But IS NULL tells you whether it is NULL or not.
I'm modifying an existing query for a client, and I've encountered a somewhat baffling issue.
Our client uses SQL Server 2008 R2 and the database in question provides the user the ability to specify custom fields for one of its tables by making use of an EAV structure. All of the values stored in this structure are varchar(255), and several of the fields are intended to store dates. The query in question is being modified to use two of these fields and compare them (one is a start, the other is an end) against the current date to determine which row is "current".
The issue I'm having is that part of the query does a CONVERT(DateTime, eav.Value) in order to turn the varchar into a DateTime. The conversions themselves all succedd and I can include the value as part of the SELECT clause, but part of the question is giving me a conversion error:
Conversion failed when converting date and/or time from character string.
The real kicker is this: if I define the base for this query (getting a list of entities with the two custom field values flattened into a single row) as a view and select against the view and filter the view by getdate(), then it works correctly, but it fails if I add a join to a second table using one of the (non-date) fields from the view. I realize that this might be somewhat hard to follow, so I can post an example query if desired, but this question is already getting a little long.
I've tried recreating the basic structure in another database and including sample data, but the new database behaves as expected, so I'm at a loss here.
EDIT In case it's useful, here's the statement for the view:
create view Festival as
select
e.EntityId as FestivalId,
e.LookupAs as FestivalName,
convert(Date, nvs.Value) as ActivityStart,
convert(Date, nve.Value) as ActivityEnd
from tblEntity e
left join CustomControl ccs on ccs.ShortName = 'Activity Start Date'
left join CustomControl cce on cce.ShortName = 'Activity End Date'
left join tblEntityNameValue nvs on nvs.CustomControlId = ccs.IdCustomControl and nvs.EntityId = e.EntityId
left join tblEntityNameValue nve on nve.CustomControlId = cce.IdCustomControl and nve.EntityId = e.EntityId
where e.EntityType = 'Festival'
The failing query is this:
select *
from Festival f
join FestivalAttendeeAll fa on fa.FestivalId = f.FestivalId
where getdate() between f.ActivityStart and f.ActivityEnd
Yet this works:
select *
from Festival f
where getdate() between f.ActivityStart and f.ActivityEnd
(EntityId/FestivalId are int columns)
I've encountered this type of error before, it's due to the "order of operations" performed by the execution plan.
You are getting that error message because the execution plan for your statement (generated by the optimizer) is performing the CONVERT() operation on rows that contain string values that can't be converted to DATETIME.
Basically, you do not have control over which rows the optimizer performs that conversion on. You know that you only need that conversion done on certain rows, and you have predicates (WHERE or ON clauses) that exclude those rows (limit the rows to those that need the conversion), but your execution plan is performing the CONVERT() operation on rows BEFORE those rows are excluded.
(For example, the optimizer may be electing to a do a table scan, and performing that conversion on every row, before any predicate is being applied.)
I can't give a specific answer, without a specific question and specific SQL that is generating the error.
One simple approach to addressing the problem would be to use the ISDATE() function to test whether the string value can be converted to a date.
That is, replace:
CONVERT(DATETIME,eav.Value)
with:
CASE WHEN ISDATE(eav.Value) > 0 THEN CONVERT(DATETIME, eav.Value) ELSE NULL END
or:
CONVERT(DATETIME, CASE WHEN ISDATE(eav.Value) > 0 THEN eav.Value ELSE NULL END)
Note that the ISDATE() function is subject to some significant limitations, such as being affected by the DATEFORMAT and LANGUAGE settings of the session.
If there is some other indication on the eav row, you could use some other test, to conditionally perform the conversion.
CASE WHEN eav.ValueIsDateTime=1 THEN CONVERT(DATETIME, eav.Value) ELSE NULL END
The other approach I've used is to try to gain some modicum of control over the order of operations of the optimizer, using inline views or Common Table Expressions, with operations that force the optimizer to materialize them and apply predicates, so that happens BEFORE any conversion in the outer query.