I want to create a table for managing versions of parameters...
In this table there is a column of type char that lets me know what version I have to use :
create table PARAMETERS_VERSION (
ID number not null,
VERSION number not null,
DATE_START date not null,
DATE_END date check(DATE_START <= DATE_END) not null
ISUSED char(1) check(ISUSED in ('Y','N')) not null,
constraint PARAMETERS_VERSION_VERSION_PK primary key (ID),
constraint PARAMETERS_VERSION_VERSION_UK unique (ISUSED)
);
How to define a unique constraint on the column ISUSED to have only a single row with the value 'Y' (and the others with 'N') ?
By the way, is my check constraint on DATE_END is correct ?
Oracle doesn't quite support partial or filtered indexes. Instead, you can use a functional index with some cleverness:
create unique index idx_parametersversion_isused
on parameters_version(case when is_used = 'Y' then -1 else id end);
That is, when is_used has any value other than Y, then the primary key is used. When it is Y, then a constant is used, so two values will conflict.
Related
The code is the category of the video, it is represented by one upper case character, excluding I, O,
Q, V, Y and Z, followed by a numeric character.
So far, I took a guess and got this. Any suggestions on how to fix it?
create table channelTable (
channelID number NOT NULL,
ChannelName varchar(100) NOT NULL,
ChannelDate date NOT NULL,
UserName varchar(100) NOT NULL UNIQUE,
TopicCode varchar(4) NOT NULL);
CONSTRAINT channelID_pk PRIMARY KEY (channelID)
CONSTRAINT c_topicCode LIKE '[A-Za-z][0-9] NOT (I,O,Q,N,Y,Z)
);
Some comments:
NOT NULL is not needed for PRIMARY KEY columns.
In Oracle, use VARCHAR2().
Then, I would suggests regular expressions. If the value is supposed to be exactly two characters, then declare it as such:
create table channelTable (
channelID number,
ChannelName varchar(100) NOT NULL,
ChannelDate date NOT NULL,
UserName varchar2(100) NOT NULL UNIQUE,
TopicCode char(2) NOT NULL;
CONSTRAINT channelID_pk PRIMARY KEY (channelID)
CONSTRAINT check (REGEXP_LIKE(c_topicCode, '^[A-HJ-NPR-UYZ][0-9]$')
);
Or perhaps more simply:
CONSTRAINT REGEXP_LIKE(c_topicCode, '^[A-Z][0-9]$') AND NOT REGEXP_LIKE(c_topicCode, '^[IOQNYZ]'))
All that said, I would rather see a table of TopicCodes that is populated with the correct values. Then you can just use a foreign key relationship to define the appropriate codes.
Use the regular expression ^[A-HJ-MPR-X]\d$ to match an upper-case character excluding I,O,Q,N,Y,Z followed by a digit:
CREATE TABLE channels (
id number CONSTRAINT channel__id__pk PRIMARY KEY,
Name varchar(100) CONSTRAINT channel__name__nn NOT NULL,
DateTime date CONSTRAINT channel__date__nn NOT NULL,
UserName varchar(100) CONSTRAINT channel__username__NN NOT NULL
CONSTRAINT channel__username__U UNIQUE,
TopicCode varchar(4),
CONSTRAINT channel__topiccode__chk CHECK ( REGEXP_LIKE( topiccode, '^[A-HJ-MPR-X]\d$' ) )
);
db<>fiddle
Also, you don't need to call the table channeltable just call it channels and you don't need to prefix the column names with the table name and you can name all the constraints (rather than relying on system generated constraint names which makes it much harder to track down issues when you are debugging).
Consider the following check constrait:
create table channelTable (
...
topicCode varchar(4) not null
check(
substr(c_topicCode, 1, 1) not in ('I', 'O', 'Q', 'V', 'Y', 'Z')
and regexp_like(topicCode, '^[A-Z]\d')
),
...
);
The first condition ensures that the code does not start with one of the forbidden characters, the second valides that it stats with an upper alphabetic character, followed by a number.
To avoid using two conditions, an alternative would be to list all allowed characters in the first position:
check(regexp_like(topicCode, '^[ABCDEFGHJKLMNPRSTUVWX]\d'))
This works in Oracle, and in very recent versions of MySQL.
I'm attempting to create a table that has three columns:
id
paid_at
failed_at
How can I make sure that paid_at can only have a value if failed_at is NULL?
Here is my current code:
CREATE TABLE charges(
id TEXT NOT NULL PRIMARY KEY,
paid_at TEXT,
failed_at TEXT
);
ALTER TABLE charges
ADD CONSTRAINT paid_at CHECK (failed_at IS NULL);
ALTER TABLE charges
ADD CONSTRAINT failed_at CHECK (paid_at IS NULL);
I also want to make sure that BOTH cannot be null.
How can I do this?
Thanks!
You can use num_nonnulls() in the check constraint:
alter table charges
add constraint only_one_not_null
check (num_nonnulls(paid_at, failed_at) = 1);
That ensure that exactly one of the columns is not null and the other is null.
If you consider a string with only spaces to be "null" as well, you could extend that to:
alter table charges
add constraint only_one_not_null
check (num_nonnulls(nullif(trim(paid_at),''), nullif(trim(failed_at),'')) = 1);
I am inclined to do this with addition. To check that one of a group of columns is not null, count the number of not-null values:
check ( (paid_at is not null)::int + (failed_at is not null)::int) > 0 )
You can use the following predicate:
alter table charges add constraint exclusive_rule check (
paid_at is null and failed_at is not null or
paid_at is not null and failed_at is null
);
I have created a table and I'm asked to add a constraint to a column called no_semesters. the condition is that the no has to be >= 0 and it should be not null with default, and the default value is 6. When I run this statement:
INSERT INTO PREMIERD08/PGM (PGM_ID, PGM_NAME)
VALUES('CPD', 'COMPUTER PROGRAMMING')
I get an error message saying column - no_semesters cant be null. why wont it set to the default value which is 6?
this was the statement -
CREATE TABLE PREMIERD08/PGM (
PGM_ID CHAR(3) NOT NULL,
PGM_NAME CHAR(40) NOT NULL,
NO_SEMESTERS NUMERIC ( 1) NOT NULL WITH DEFAULT 6,
CONSTRAINT PGM_PGM_NAME_UK UNIQUE (PGM_NAME),
CONSTRAINT PGM_PGM_ID_CK CHECK (PGM_ID IN ('CPA', 'CPD') ),
CONSTRAINT PGM_PGM_ID_PK PRIMARY KEY (PGM_ID), CONSTRAINT PGM_NO_SEMESTERS_CK CHECK (NO_SEMESTERS >= 0)
)
Your code works in Db2 (for LUW) - the only thing to change is the table name needs to be in "" because of the /
CREATE TABLE "PREMIERD08/PGM" .....
INSERT INTO "PREMIERD08/PGM" (PGM_ID, PGM_NAME)
VALUES('CPD', 'COMPUTER PROGRAMMING')
I have the following table.
CLASS_HAS_STUDENTS (
PER_SSN INTEGER NOT NULL,
PER_YEAR INTEGER NOT NULL, /*These two are PKs for a student*/
SCHOOL_CODE INTEGER NOT NULL, /*PK for a school*/
CLASS_YEAR INTEGER NOT NULL,
CLASS_NUMBER INTEGER NOT NULL,
CLASS_TEACHTYPE CHAR(3) NOT NULL, /*These three are PKs for a class*/
STUDCLASS_STATUS CHAR(1) NOT NULL
constraint CKC_STUDCLASS_STATUS_CLASS_TI check (StudClass_Status IN ('E', 'Y', 'T', 'P', 'F')),
STUDCLASS_LISTNUMBER INTEGER NOT NULL,
STUDCLASS_ROLLNUMBER INTEGER NOT NULL
);
(This code lacks some minor constraints)
Now, I need a way to check that one PER_SSN/PER_YEAR (a person's PK) can only have one 'E' ("Enrolled") status. I can't do this with a trigger (given I'm selecting from the same table) and I don't know if I can do this with a check constraint (can I use COUNT() here?). Any help is appreciated.
You can create a function-based unique index to enforce this sort of thing. You can't create a constraint as such.
This takes advantage of the fact that Oracle b-tree indexes do not index NULL data so the index will only have entries for the rows where studclass_status is E.
CREATE UNIQUE INDEX idx_one_enrolled
ON class_has_students( CASE WHEN studclass_status = 'E'
THEN per_ssn
ELSE null
END,
CASE WHEN studclass_status = 'E'
THEN per_year
ELSE null
END );
I'm a little confused by your question. I'm guessing you either want to:
1) Prevent insert of more than one status per student (in which case a trigger would be appropriate)
or
2) Use a SELECT statement to find students already in the table, in which case you want to do something like:
SELECT PER_SSN, PER_YEAR, STUDCLASS_STATUS, COUNT(*)
FROM CLASS_HAS_STUDENTS
WHERE STUDCLASS_STATUS = 'E'
HAVING COUNT(*) > 1
GROUP BY PER_SSN, PER_YEAR, STUDCLASS_STATUS;
You should be able to do this with a partial unique index. To make sure you only have one enrolled class for every ssn this should work:
CREATE UNIQUE INDEX ssn_enrollments ON class_has_students(per_ssn)
WHERE studclass_status='E';
Note that this feature is not supported in all SQL implementations, but PostgreSQL has supported since at least version 8.
I'm creating a table with:
CREATE TABLE movies
(
id INT AUTO_INCREMENT PRIMARY KEY,
name CHAR(255) NOT NULL,
year INT NOT NULL,
inyear CHAR(10),
CONSTRAINT UNIQUE CLUSTERED (name, year, inyear)
);
(this is jdbc SQL)
Which creates a MySQL table with a clustered index, "index kind" is "unique", and spans the three clustered columns:
mysql screen http://img510.imageshack.us/img510/930/mysqlscreenshot.th.jpg
full size
However, once I dump my data (without exceptions thrown), I see that the uniqueness constraint has failed:
SELECT * FROM movies
WHERE name = 'Flawless' AND year = 2007 AND inyear IS NULL;
gives:
id, name, year, inyear
162169, 'Flawless', 2007, NULL
162170, 'Flawless', 2007, NULL
Does anyone know what I'm doing wrong here?
MySQL does not consider NULL values as equal; hence, why the unique constraint appears to not be working. To get around this, you can add a computed column to the table which is defined as:
nullCatch as (case when inyear is null then '-1' else inyear)
Substitute this column in for 'inyear' in the constraint:
CONSTRAINT UNIQUE CLUSTERED (name, year, nullCatch)