I want an output to show how many alumni attended the event
I got Event Table
CREATE TABLE EVENT
(EVENTID INTEGER CONSTRAINT EVENT_ID_PK PRIMARY KEY,
EDATEANDTIME VARCHAR2(20),
EVENUE VARCHAR2(30),
EAUDIENCE VARCHAR2(30),
EATTENDED VARCHAR2(30),
EVENT_ALUMNI INTEGER,
CONSTRAINT EVENT_ALUMNI_FK FOREIGN KEY (EVENT_ALUMNI) REFERENCES
ALUMNI(ALUMNIID));
Here is what I inserted in Event
INSERT INTO EVENT VALUES(25993, 'Jan 14, 2015', 'Concorde Hall', 'Tobias, Tucker, Felix, Nicole, Desiree, Taylor, Frant, Ifeoma, Forrest, Stewart, Cole, Arthur, Thomas, Bo, Lucian',
'Tobias, Tucker, Felix, Nicole, Desiree, Taylor, Frant, Ifeoma, Forrest, Stewart, Cole, Arthur, Thomas, Bo',17337);
INSERT INTO EVENT VALUES(23823, 'July 18 2015', 'Rochester Hotel', 'Joan, Thalia, Haleeda', 'Joan, Haleeda'
,19927);
And I have a View Statement to view how many attended
CREATE VIEW VIEWH AS SELECT ETYPE, EDATEANDTIME, COUNT (*) EATTENDED FROM EVENT
WHERE EDATEANDTIME LIKE '%2015%' AND ETYPE = 'Social'
GROUP BY ETYPE, EDATEANDTIME, EATTENDED;
Here is where I got problem. When i run the query, the output is I got only one who attended the event instead of like 10 or 15
I want to know where i went wrong.
There are several potential problems with your setup, I mentioned a couple in a Comment to your question.
Regarding the count specifically: your first problem is you have EATTENDED in the GROUP BY clause. Why? This almost surely means that each group is exactly one row.
Then your next problem is counting tokens out of a comma-separated string. One way is using regexp_count() as TheGameiswar has shown. (err... his/her solution has disappeared? anyway, I was saying...)
Another is to use length() and translate():
select ... , 1 + length(EATTENDED) - length(translate(EATTENDED, ',', '') as ATT_CNT ...
A couple of notes about this:
The length difference, just like regexp_count(), counts commas in the string. You add one to count tokens (you don't care how many commas there are, you care how many names are separated by commas). translate() works faster than regexp_count() (all regexp functions are very powerful, but slower, so they should be used only when they are really needed, IF performance is important); length doesn't add much overhead since in Oracle the length of VARCHAR2 is always calculated and stored as part of the internal representation of a string.
I gave a different alias to the resulting column; in your original query you use the same name, EATTENDED, for a column in your base table and as an alias for this numeric column in your view. You can do it, it's legal, but it is almost certain to cause problems in the future.
It is because COUNT gives number of "rows" in the result and not number of "values in column".
To give you a simple example
example1_table:
col1
--------
a
b
c
SELECT COUNT(col1) FROM example1_table; // The result is 3, as there are three rows
example2_table:
col1
--------
a,b,c
SELECT COUNT(col1) FROM example1_table; // The result is 1, as there is only one row (it is not about number of values in it)
Note:
As stated by #mathguy you could have used a better Database structure.
Instead of using only one table EVENT create two tables let they be: table1 table2 so you could avoid redundancy.
CREATE TABLE table1
(EVENTID INTEGER CONSTRAINT EVENT_ID_PK PRIMARY KEY,
EDATEANDTIME VARCHAR2(20),
EVENUE VARCHAR2(30),
EVENT_ALUMNI INTEGER,
CONSTRAINT tab1_FK FOREIGN KEY (EVENT_ALUMNI) REFERENCES
ALUMNI(ALUMNIID));
CREATE TABLE table2
(
EAUDIENCE VARCHAR2(30),
EATTENDED VARCHAR2(30),
tab2ID INTEGER
CONSTRAINT tab2_FK FOREIGN KEY (tab2ID) REFERENCES
tab1(EVENT_ALUMNI));
If you don't want to make any changes in your table, assuming there is always a comma present between two attendees names you could try:
CREATE VIEW VIEWH AS SELECT ETYPE, EDATEANDTIME, regexp_count(EATTENDED,',')+1 FROM EVENT WHERE EDATEANDTIME LIKE '%2015%' AND ETYPE = 'Social' GROUP BY ETYPE, EDATEANDTIME;
Related
I know that the question is very long and I understand if someone doesn't have the time to read it all, but I really wish there is a way to do this.
I am writing a program that will read the database schema from the database catalog tables and automatically build a basic application with the information extracted from the system catalogs.
Many tables in the database can be just a list of items of the form
CREATE TABLE tablename (id INTEGER PRIMARY KEY, description VARCHAR NOT NULL);
so when a table has a column that references the id of tablename I just resolve the descriptions by querying it from the tablename table, and I display a list in a combo box with the available options.
There are some tables however that cannot directly have a description column, because their description would be a combination of other columns, lets take as an example the most important of those tables in my first application
CREATE TABLE bankaccount (
bankid INTEGER NOT NULL REFERENCES bank,
officeid INTEGER NOT NULL REFERENCES bankoffice,
crc INTEGER NOT NULL,
number BIGINT NOT NULL
);
this as many would know, would be the full account number for a bank account, in my country it's composed as follows
[XXXX][XXXX][XX][XXXXXXXXXX]
^ ^ ^ ^
bank id | crc account number
|
|_ bank office id
so that's the reason of the way my bankaccount table is structured as is.
Now, I would like to have the complete bank account number in a description column so I can display it in the application without giving a special treatment to this situation, since there are some other tables with similar situation, something like
CREATE TABLE bankaccount (
bankid INTEGER NOT NULL REFERENCES bank,
officeid INTEGER NOT NULL REFERENCES bankoffice,
crc INTEGER NOT NULL,
number BIGINT NOT NULL,
description VARCHAR DEFAULT bankid || '-' || officeid || '-' || crc || '-' || number
);
Which of course doesn't work since the following error is raised1
ERROR: cannot use column references in default expression
If there is any different approach that someone can suggest, please feel free to suggest it as an answer.
1 This is the error message given by PostgreSQL.
What you want is to create a view on your table. I'm more familiar with MySQL and SQLite, so excuse the differences. But basically, if you have table 'AccountInfo' you can have a view 'AccountInfoView' which is sort of like a 'stored query' but can be used like a table. You would create it with something like
CREATE VIEW AccountInfoView AS
SELECT *, CONCATENATE(bankid,officeid,crc,number) AS FullAccountNumber
FROM AccountInfo
Another approach is to have an actual FullAccountNumber column in your original table, and create a trigger that sets it any time an insert or update is performed on your table. This is usually less efficient though, as it duplicates storage and takes the performance hit when data are written instead of retrieved. Sometimes that approach can make sense, though.
What actually works, and I believe it's a very elegant solution is to use a function like this one
CREATE FUNCTION description(bankaccount) RETURNS VARCHAR AS $$
SELECT
CONCAT(bankid, '-', officeid, '-', crc, '-', number)
FROM
bankaccount this
WHERE
$1.bankid = this.bankid AND
$1.officeid = this.officeid AND
$1.crc = this.crc AND
$1.number = this.number
$$ LANGUAGE SQL STABLE;
which would then be used like this
SELECT bankaccount.description FROM bankaccount;
and hence, my goal is achieved.
Note: this solution works with PostgreSQL only AFAIK.
I've been handed a very specific business requirement, and I'm having trouble translating it to work within our database.
We have multiple departments, who all deal with what we call files. Each file has a unique identifier, but how this identifier is assigned depends on the department that the file is associated with.
Departments ABC, DEF and GHI need the system to provide them with the next identifier following a pattern... while departments JKL and MNO need to be able to specify their own identifiers.
This is further compounded by the fact that the generated file numbers are semi complex. Their file numbers follow the pattern:
[a-z]{3,4}\d{2}-\d{4}
(A 3 or 4 letter prefix that corresponds to the department with two digits corresponding to the year, a dash followed by a four digit generated number - i.e. ABC13-0001)
The part before the dash is easy to generate... the file table has a mandatory foreign key reference to a department table that has the prefix column, and I can grab the year just as easily. it's the part after the dash that I can't seem to work out.
It's a four digit identifier. Each department needs the next generated ID to be as sequential to their department as possible (I say as sequential as possible, as I'm aware that even identity specifications can leave gaps). On top of that, we need to reset it back to 0001 each year. All of that, while ensuring that there are no duplicates, which is the most important part of all of this.
So, we only have one file table that is used by all of these departments. As such, to be able to handle JKL and MNO, I have the FileNumber field set to varchar(12) with a unique constraint. They can type in whatever they need, so long as it's unique. That just leaves me with how to generate the unique file numbers for the other departments.
My first instinct is to give the file table a surrogate identity primary key to make sure that, even if something goes wrong with the generated file number, that each record is guaranteed a unique identifier.
Then I would create a single row table that has two columns per department, one for a number and one for a date. The number would be the last used number for the 4 digit identifier suffix for a given department (as an int), and the date would be when it was assigned. Storing the date would let me check if the year has changed since the last id was pulled so that I can assign 1, instead of lastid + 1.
Then an insert trigger on the file table would generate the file id using:
The foreign key to the department table to get the department prefix
CONVERT(VARCHAR, YEAR( GETDATE() ) % 100) to pull the current two digit year
A select to the above described utility table to get the last id + 1 (or reseting to 1 if the current year differs from the year of the last updated date).
The trigger would finally update the utility table with the last used id and date.
In theory, I think that would work... and the unique constraint on the file id column would prevent an insert where the generated file id already exists. But it feels so brittle, and I can foresee that unique constraint being a double edged sword that would possibly prevent a department from creating a new file should the trigger fail to update the utility table. After all, if it doesn't, then the next time a file number is generated, it would try to use the same generated id, and fail. There must be a better way.
My other thought was to have a table per department with just an identity integer column and non-null date field with a default of (getdate())... and have the trigger on the file table insert a new row, and use that id. It would also be responsible for deleting all rows in the given department id table and reset the identity come the new year. It feels more secure to me, but then I have 5 utility tables (1 per department that auto-generate ids) with up to 9999 records, just to generate an id.
Am I missing something simple? Am I going about this the right way? I just can't help but think that there must be an easier way. Am I right to try to make the SQL server responsible for this, or should I try doing this in the desktop application that I will build on top of this database?
So, I think it's possible you're overcomplicating this. It's also possible I'm misunderstanding the requirements. I don't believe you need separate tables or anything, you just need to check the existing IDs and increment them. SQLFiddle doesn't seem to be working right now, but here's a method I came up with in my local DB:
create table dept_ids (
id varchar(12) primary key
)
insert into dept_ids values('ABC13-0001')
insert into dept_ids values('DEF13-0001')
insert into dept_ids values('GHI13-0001')
insert into dept_ids values('JKL13-0001')
insert into dept_ids values('ABC13-0002')
declare
#dept varchar(4)
, #year varchar(2)
, #prefix varchar(8)
, #new_seq int
set #dept = 'ABC'
select #year = right(cast(DATEPART(yy, getdate()) as varchar(4)), 2)
set #prefix = #dept + #year + '-'
select #new_seq = isnull(right(max(id), 4), 0) + 1 from dept_ids where id like #prefix + '%'
select new_id = #prefix + right(replicate('0', 4) + cast(#new_seq as varchar(4)), 4)
This handles the different departments of course, as well as the year scenario by using getdate() and an ISNULL check. For the departments that can enter their own sequence values, you can just add a null check for that parameter and skip generating this value if it's present.
If I'm oversimplifying, feel free to let me know and I'll adjust.
I have the following constraint:
ALTER TABLE Movie
ADD CONSTRAINT NomsRANGE
CHECK (totalNoms BETWEEN 0 AND 20);
...and used the following to try and test it:
INSERT INTO Movie
(totalNoms)
VALUES
('23');
I get the following error:
cannot insert NULL into ("ALI"."MOVIE"."MOVIEID")
My scheme is:
Actor (actorID, lastName, firstName, middleName, suffix, gender, birthDate, deathDate)
Movie (movieID, title, year, company, totalNoms, awardsWon, DVDPrice, discountPrice)
Quote (quoteID, quote)
Role (roleID ,roleName ,gender ,actorID* ,movieID*)
RoleQuote (roleID*, quoteID*)
And my relationships are:
CONSTRAINT_NAME C
------------------------------ -
QUOTE_FK R
ROLE_FK R
MOVIE_ROLE_FK R
ACTOR_ROLE_FK R
ACTORID P
MOVIEID P
QUOTEID P
ROLEID P
ROLEQUOTEID P
9 rows selected.
Answer:
The answer was simple none of you spotted this it took me all day but i solved it so am posting solution so it helps others.
INSERT INTO Movie(movieID, totalNoms)
VALUES('049', '22');
I missed the first value which was the primary key as the error was saying:
cannot insert NULL into ("ALI"."MOVIE"."MOVIEID")
When i entered a new primary key it showed the constraint was violated
Thank you guys for all the help
If you omit columns in an INSERT statement, the database still needs to fill the column for that row. Which would be NULL, unless you setup a DEFAULT constraint/etc for each column.
The error is telling you that MOVIE.movieid does not accept NULL, which is good. It sounds like you need to setup the sequence to populate the value, or provide logic for however you want MOVIE.movieid populated (far less ideal). The sequence can either be referenced in the INSERT statement to fill the value, or you can look at triggers/default constraints to handle things in the background.
You'll have to figure out how you want/need to handle any other errors relating to column NULLability. Only after this is done, will you be able to see if your CHECK constraint works -- there's a little concern about if the value is provided as a string, if Oracle will implicitly convert it to an INT/NUMERIC data type.
1) The specific error is telling you that your INSERT statement needs to specify the MovieID. If you have created sequences to generate your synthetic primary key values, you'd want something like this (assuming there are no other NOT NULL columns in the Movie table)
INSERT INTO Movie
(movieID, totalNoms)
VALUES
(movieId_seq.nextval, 23);
2) Assuming that totalNoms is a NUMBER since your check constraint is treating it like a number, you would want to insert the number 23 rather than the string 23. Forcing Oracle to do implicit conversions is never a good idea-- it probably won't matter on a simple INSERT like this but if you get in the habit of using numbers when you're dealing with numeric fields and strings when you're dealing with character fields, life will be a lot easier.
Q: Is there any way to implement self-documenting enumerations in "standard SQL"?
EXAMPLE:
Column: PlayMode
Legal values: 0=Quiet, 1=League Practice, 2=League Play, 3=Open Play, 4=Cross Play
What I've always done is just define the field as "char(1)" or "int", and define the mnemonic ("league practice") as a comment in the code.
Any BETTER suggestions?
I'd definitely prefer using standard SQL, so database type (mySql, MSSQL, Oracle, etc) should't matter. I'd also prefer using any application language (C, C#, Java, etc), so programming language shouldn't matter, either.
Thank you VERY much in advance!
PS:
It's my understanding that using a second table - to map a code to a description, for example "table playmodes (char(1) id, varchar(10) name)" - is very expensive. Is this necessarily correct?
The normal way is to use a static lookup table, sometimes called a "domain table" (because its purpose is to restrict the domain of a column variable.)
It's up to you to keep the underlying values of any enums or the like in sync with the values in the database (you might write a code generator to generates the enum from the domain table that gets invoked when the something in the domain table gets changed.)
Here's an example:
--
-- the domain table
--
create table dbo.play_mode
(
id int not null primary key clustered ,
description varchar(32) not null unique nonclustered ,
)
insert dbo.play_mode values ( 0 , "Quiet" )
insert dbo.play_mode values ( 1 , "LeaguePractice" )
insert dbo.play_mode values ( 2 , "LeaguePlay" )
insert dbo.play_mode values ( 3 , "OpenPlay" )
insert dbo.play_mode values ( 4 , "CrossPlay" )
--
-- A table referencing the domain table. The column playmode_id is constrained to
-- on of the values contained in the domain table playmode.
--
create table dbo.game
(
id int not null primary key clustered ,
team1_id int not null foreign key references dbo.team( id ) ,
team2_id int not null foreign key references dbo.team( id ) ,
playmode_id int not null foreign key references dbo.play_mode( id ) ,
)
go
Some people for reasons of "economy" might suggest using a single catch-all table for all such code, but in my experience, that ultimately leads to confusion. Best practice is a single small table for each set of discrete values.
add a foreign key to "codes" table.
the codes table would have the PK be the code value, add a string description column where you enter in the description of the value.
table: PlayModes
Columns: PlayMode number --primary key
Description string
I can't see this as being very expensive, databases are based on joining tables like this.
That information should be in database somewhere and not on comments.
So, you should have a table containing that codes and prolly a FK on your table to it.
I agree with #Nicholas Carey (+1): Static data table with two columns, say “Key” or “ID” and “Description”, with foreign key constraints on all tables using the codes. Often the ID columns are simple surrogate keys (1, 2, 3, etc., with no significance attached to the value), but when reasonable I go a step further and use “special” codes. Following are a few examples.
If the values are a sequence (say, Ordered, Paid, Processed, Shipped), I might use 1, 2, 3, 4, to indicate sequence. This can make things easier if you want to find all “up through” a give stages, such as all orders that have not yet been shipped (ID < 4). If you are into planning ahead, make them 10, 20, 30, 40; this will allow you to add values “in between” existing values, if/when new codes or statuses come along. (Yes, you cannot and should not try to anticipate everything and anything that might have to be done some day, but a bit of pre-planning like this can make some changes that much simpler.)
Keys/Ids are often integers (1 byte, 2 byte, 4 byte, whatever). There’s little cost to make them character values (1 char, 2 char, 3, char, 4 char). That’s character, not variable character. Done this way, you can have mnemonics on your codes, such as
O, P, R, S
Or, Pd, Pr, Sh
Ordr, Paid, Proc, Ship
…or whatever floats your boat. Done this way, I have found that it can save a lot of time when analyzing or debugging. You still want the lookup table, for relational integrity as well as a reminder for the more obscure codes.
I want to use a database like:
table wrongdoer (primarykey integer
ID, date)
table crime (numeric
foreign_key_to_wrongdoer, text crime)
I want my application (in python) to register a wrongdoer (which should give the entry a unique integer) and register the first crime against him. My idea is rather clumsy:
insert into wrongdoer(...)
id=cur.execute("select max(ID)")
//this is to select the most recent ID
cur.execute("insert into
crime('"+id+"'"crime+"'")")
That is, insert an entry, select its unique key from DB (assuming its the highest number), and then use it for the subsequent queries. Is there a better way to do it?
Check this function out:
http://www.sqlite.org/c3ref/last_insert_rowid.html