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.
Related
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.
insert into employee(eid,dojo) SELECT
14,coalesce(to_char(dojo,'dd-mm-yyyy'),'')
from employee;
I have to insert into table by selecting it from table,my column dojo has not null constraint and timestamp doesn't allow '' to insert please provide an alternate for this if timestamp is null from select query
Your current query has severals problems, two of which I think my answer can resolve. First, you are trying to insert an empty string '' to handle NULL values in the dojo column. This won't work, because empty string is not a valid timestamp. As others have pointed out, one solution would be to use current_timestamp as a placeholder.
Another problem you have is that you are incorrectly using to_char to format your timestamp data. The output of to_char is a string, and the way you are using it would cause Postgres to reject it. Instead, you should be using to_timestamp(), which can parse a string and return a timestamp. Something like the following is what I believe you intend to do:
insert into employee (eid, dojo)
select 14, coalesce(to_timestamp(dojo, 'DD/MM/YYYY HH:MI:SS PM'), current_timestamp)
from employee;
This assumes that your timestamp data is formatted as follows:
DD/MM/YYYY HH:MI:SS PM (e.g. 19/2/1995 12:00:00 PM)
It also is not clear to me why you are inserting back into the employee table which has non usable data, rather than inserting into a new table. If you choose to reuse employee you might want to scrub away the bad data later.
you can use some default date value like 1st jan 1900 or now()
your query should be like
insert into employee(eid,dojo) SELECT
14,coalesce(to_char(dojo,'dd-mm-yyyy'),now())
from employee;
There is no such thing as a non-null yet blank timestamp. NULL = blank.
There is literally nothing you can do but store a valid timestamp or a null. Since you have a non-null constraint your only option is to pick a default timestamp that you consider "blank".
Using a hard coded date to indicate a blank value is a terrible terrible terrible idea btw. If it is blank, remove the not null constraint, make it null and move on.
I am not trying to be condescending but I do not think you understand nulls. See here
https://en.wikipedia.org/wiki/Null_(SQL)
I have a column saved as a character data type. This column is what I am going to be using as a date. The column goes "YYYY-MM-DD" in that format.
This is a problem because if I ever need to filter by date, I have to go
select col_1, col_2
from table
where date LIKE '2016-04%;
If I want to search for a date range, this turns into a giant complicated mess.
What is the easiest way to convert this to a "date" data type? I want it to continue to be in YYYY-MM-DD order (no timestamp).
My ultimate goal is to be able to search for dates in a format like this:
select col_1, col_2
from table
where date between 2016-01-01 AND 2016-05-31;
What do you guys recommend? I am terrified I am going to corrupt my date if I use an alter statement to convert my data type. (I have a copy of the data saved and can upload it again, but it will take forever.)
Edit: This is a VERY Large table.
Edit Part 2: I originally stored the data as a varchar data type because my dates were not uploading correctly and I got an error message when I tried to save as a date data type. The every date in this column is in the "YYYY-MM-DD" order. My solution was to save it as varchar to avoid the error message (I couldn't figure out what was wrong. I even got rid of leading and trailing spaces.)
Storing a date as a varchar was the wrong choice to begin with. It's very good that you want to change that.
The first step is to convert the columns using an ALTER TABLE statement:
alter table the_table
ALTER COLUMN col_1 TYPE date using col_1::date,
ALTER COLUMN col_2 TYPE date using col_2::date;
Note that this will fail if you have any value in those columns that cannot be convert to a correct date. If you get that you need to first fix those invalid strings before you can change the data type.
I want it to continue to be in YYYY-MM-DD order
This is a misconception. A DATE (or timestamp) does not have a "format". Once it's stored as a date you can display it in any format you want.
My ultimate goal is to be able to search for dates in a format like this:
2016-01-01 is not a valid date literal, a proper (i.e. correctly typed) date constant can be specified e.g. using date '2016-01-01' (note the single quotes!
So your query becomes:
select col_1, col_2
from table
where col_1 between date '2016-01-01' AND date '2016-05-31';
If you have a lot of queries like that you should consider creating an index on the date columns.
Regarding the date constant format:
Are you telling me that despite having the varchar data types, I can still (as of right now) search between specific dates by just typing the word date and putting single quotes between two dates
No, that's not the case. SQL is a strongly typed language and as such will only compare values of the same type.
Using an ANSI date literal (or e.g. to_date()) results in a type constant (i.e. a value with a specific data type).
The difference between date '2016-01-01' and '2016-01-01' is the same as between42(a number) and'42'` (a string).
If you compare a string with a date, you are comparing apples and oranges and the database will do an implicit data type conversion from one type to the other. This is something that should be avoided at all costs.
If you do not want to change the table, you should use the query sagi provided which explicitly converts the strings to dates and then does the comparison on (real) date values (not strings)
You can use POSTGRES TO_DATE() cast function :
SELECT col_1,col_2
FROM Your_Table
WHERE to_date(date_col,'yyyy-mm-dd') between to_date('2016-05-31','yyyy-mm-dd') and to_date('2016-01-01','yyyy-mm-dd')
What #a_horse said.
Plus, if you can't change the data type for some odd reason, to_date() is a safe option to convert the column on the column, but there is no point to use the same expression for provided constants. So:
SELECT col_1, col_2
FROM tbl
WHERE to_date(date, 'YYYY-DD-MM') BETWEEN date '2016-05-31' AND date '2016-01-01';
Or just use string literals without type. The type date is deferred from the context in this expression. And you don't even need to_date(). Since you are using ISO format already. A plain cast is safe:
WHERE date::date BETWEEN '2016-05-31' AND '2016-01-01';
Be sure to use ISO 8601 format for all date strings, so they are unambiguous and valid with any locale.
You can even have an expression index to support the query. Match the actual expression used in queries:
CREATE INDEX tbl_date_idx ON tbl ((date::date)); -- parentheses required!
But I wouldn't use the basic type name date as identifier to begin with.
I have created a table with a column date_time type (varchar2 (40) ) but when i try to insert the current system date and time the doesnt work it gives error (too many values). please tell me what's wrong with the insert statement.
create table HR (type varchar2 (20), raised_by number (6), complaint varchar2 (500), date_time varchar2(40))
insert into HR values ('request',6785,'good morning',sysdate,'YYYY/MM/DD:HH:MI:SSAM')
The immediate cause of the error is that you have too many values, as the message says; that is, more elements in your values clause than there are columns. It is better to explicitly list the column names to avoid future problems and confusion, so you're really doing this:
insert into HR (type, raised_by, complaint, date_time)
values ('request',6785,'good morning',sysdate,'YYYY/MM/DD:HH:MI:SSAM')
... sp you have four columns, but five values. You're trying to insert the current date/time as a string so you would need to use the to_char() function:
insert into HR (type, raised_by, complaint, date_time)
values ('request',6785,'good morning',
to_char(sysdate,'YYYY/MM/DD:HH:MI:SSAM'))
But it is bad practice to store a date (or any other structured data, such as a number) as a string. As the documentation notes:
Each value manipulated by Oracle Database has a data type. The data
type of a value associates a fixed set of properties with the value.
These properties cause Oracle to treat values of one data type
differently from values of another. For example, you can add values of
NUMBER data type, but not values of RAW data type.
If you use a string then you can put invalid values in. If you use a proper DATE data type then you cannot accidentally put an invalid or confusing value in. Oracle will also be able to optimise the use of the column, and will be able to compare values safely and efficiently. Although the format you're using is better than some, using string comparison you still can't easily compare two values to see which is earlier, so you can't properly order by the date_time column for example.
Say you inserted two rows with values 2013/11/15:09:00:00AM and 2013/11/15:08:00:00PM - which is earlier? You need to look at the AM/PM marker to realise the first one is earlier; with a string comparison you'd get it wrong because 8 would be sorted before 9. Using HH24 instead of HH and AM avoids that, but would still be less efficient than a true date.
If you need to store a date with a time component you can use the DATE data type, which has precision down to the second; or if you need fractional seconds too then you can use TIMESTAMP. Then your table and insert would be:
create table HR (type varchar2 (20), raised_by number (6),
complaint varchar2 (500), date_time date);
insert into HR (type, raised_by, complaint, date_time)
values ('request',6785,'good morning',sysdate);
You can still get the value in the format you wanted for display purposes as part of a query:
select type, raised_by, complaint,
to_char(date_time, 'YYYY/MM/DD:HH:MI:SSAM') as date_time
from HR
order by date_time;
TYPE RAISED_BY COMPLAINT DATE_TIME
-------------------- ---------- -------------------- ---------------------
request 6785 good morning 2013/11/15:08:44:35AM
Only treat a date as a string for display.
You can use TO_DATE() or TO_TIMESTAMP or To_char() function,
insert into HR values ('request',6785,'good morning',TO_DATE(sysdate, 'yyyy/mm/dd hh24:mi:ss'))
insert into HR values ('request',6785,'good morning',TO_TIMESTAMP(systimestamp, 'yyyy/mm/dd hh24:mi:ss'))
sysdate - It will give date with time.
systimestamp - It will give datetime with milliseconds.
To_date() - Used to convert string to date.
To_char() - Used to convert date to string.
Probably here you have to use To_char() because your table definition have varchar type for date_time column.
Use TIMESTAMP datatype for date_time. And while inserting use the current timestamp.
create table HR (type varchar2(20), raised_by number(6), complaint varchar2(500), date_time timestamp);
insert into HR values ('request',6785,'good morning', systimestamp);
For other options: http://psoug.org/reference/timestamp.html
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.