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
);
Related
I have a table:
CREATE TABLE ProjectCreationTasks
(
Id text NOT NULL PRIMARY KEY,
ProjectName text,
ProjectCode text,
DenialReason text
);
An administrator can approve or deny a project creation request. To approve, the admin sets both a ProjectName and ProjectCode; to deny, the admin sets a DenialReason.
How can I add a constraint such that:
Name, Code, Reason can all be null simultaneously
If both Name and Code has a value then Reason must be null
If Reason has a value, then both Name and Code must be null
Thank you in advance.
You could use CHECK constaint to implement this kind of logic:
CREATE TABLE ProjectCreationTasks (
Id text NOT NULL PRIMARY KEY,
ProjectName text,
ProjectCode text,
DenialReason text,
CONSTRAINT my_constraint CHECK
((ProjectName IS NULL AND ProjectCode IS NULL AND DenialReason IS NULL)
OR(ProjectName IS NOT NULL AND ProjectCode IS NOT NULL AND DenialReason IS NULL)
OR(DenialReason IS NOT NULL AND ProjectName IS NULL AND ProjectCode IS NULL))
);
DBFiddle Demo
The answer from Lukasz Szozda is correct as modified in my comment (the problem statement is slightly ambiguous). A slightly shorter equivalent clause that might be harder to read is
CONSTRAINT my_constraint CHECK
((ProjectName IS NULL = ProjectCode IS NULL) -- go together
AND (ProjectCode IS NULL OR DenialReason IS NULL) -- allow both NULL but disallow both NOT NULL
);
I am using Oracle Express, and I'd like to make a statement to add a check constraint to my Invoices table that allows Payment_Date to be NULL if Payment_Total = 0, AND Payment_Date to be NOT NULL if Payment_Total > 0.
I only understand how to alter a table to add a constraint that checks that a column's value. I don't understand how to make constraints that Allow null values or disallow null values if a certain condition (ColumnValue > SomeValue) is met.
Here is how you can express the check constraint:
alter table t add constraint ck_values
check ((payment_date is null and payment_total = 0) or
(payment_date is not null and payment_total > 0)
);
I want to ensure that only the values 'Expert', 'Average' or 'Adequate' are entered into the levelOfExpertise column of this table, however whenever I do try an enter one of those values, it returns an error saying the value entered is too short. Here is the create table query for this particular table. The the column I am referring to is levelOfExpertise:
CREATE TABLE MusicianInstrument
(
musicianNo varchar(5) not null
CONSTRAINT MI_PK1 REFERENCES Musician(musicianNo),
instrumentName varchar(50) not null
CONSTRAINT MI_PK2 REFERENCES Instrument(instrumentName),
levelOfExpertise varchar(50),
CONSTRAINT levelOfExpertise CHECK (levelOfExpertise = 'Expert', 'Adequate', 'Avergage'),
PRIMARY KEY(musicianNo,instrumentName)
);
Any ideas how I can ensure only those three values (Expert, Adequate or Average) can be entered?
Thanks
Use the IN operator
CHECK (levelOfExpertise IN ('Expert','Adequate','Avergage'))
Try to change your CHECK constraint as following:
CONSTRAINT levelOfExpertise CHECK (levelOfExpertise IN ('Expert','Adequate','Avergage'))
I suppose that you use sql server as RDBMS.
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.
I use SQL Server 2008
I use a CHECK CONSTRAINT on multiple columns in the same table to try to validate data input.
I receive an error:
Column CHECK constraint for column
'AAAA' references another column,
table 'XXXX'.
CHECK CONSTRAINT does not work in this way.
Any other way to implement this on a single table without using FK?
Thanks
Here an example of my code
CREATE TABLE dbo.Test
(
EffectiveStartDate dateTime2(2) NOT NULL,
EffectiveEndDate dateTime2(2) NOT NULL
CONSTRAINT CK_CmsSponsoredContents_EffectiveEndDate CHECK (EffectiveEndDate > EffectiveStartDate),
);
Yes, define the CHECK CONSTRAINT at the table level
CREATE TABLE foo (
bar int NOT NULL,
fred varchar(50) NOT NULL,
CONSTRAINT CK_foo_stuff CHECK (bar = 1 AND fred ='fish')
)
You are declaring it inline as a column constraint
...
fred varchar(50) NOT NULL CONSTRAINT CK_foo_fred CHECK (...)
...
Edit, easier to post than describe. Fixed your commas.
CREATE TABLE dbo.Test
(
EffectiveStartDate dateTime2(2) NOT NULL,
EffectiveEndDate dateTime2(2) NOT NULL, --need comma
CONSTRAINT CK_CmsSponsoredContents_EffectiveEndDate CHECK (EffectiveEndDate > EffectiveStartDate) --no comma
);
Of course, the question remains are you using a CHECK constraint where it should be an FK constraint...?
Check constraints can refer to a single column or to the whole record.
Use this syntax for record-level constraints:
ALTER TABLE MyTable
ADD CONSTRAINT MyCheck
CHECK (...your check expression...)
You can simply apply your validation in a trigger on the table especially that either way the operation will be rolled back if the check failed.
I found it more useful for CONSTRAINT using case statements.
ALTER TABLE dbo.ProductStock
ADD
CONSTRAINT CHK_Cost_Sales
CHECK ( CASE WHEN (IS_NOT_FOR_SALE=0 and SAL_CPU <= SAL_PRICE) THEN 1
WHEN (IS_NOT_FOR_SALE=1 ) THEN 1 ELSE 0 END =1 )