One or the other attribute. For example:
CREATE TYPE example AS(
var1 TEXT,
var2 TEXT);
If they have input for var1 they can't have a value for var2.
Use a check constraint:
ALTER TABLE example
ADD CHECK (val1 IS NULL OR val2 IS NULL);
This allows for both columns to be NULL, but you can easily change the condition to prevent that.
you can create the CHECK of your custom data type in the table itself:
CREATE TABLE t (
txt example,
CONSTRAINT one_var_null
CHECK (((txt).var1 IS NULL AND (txt).var2 IS NOT NULL) OR
((txt).var1 IS NOT NULL AND (txt).var2 IS NULL))
);
EDIT: much more elegant alternative suggested by #a_horse_with_no_name (num_nonnulls)
CREATE TABLE t (
txt example,
CONSTRAINT one_var_null
CHECK (num_nonnulls((txt).var1, (txt).var2) = 1)
);
Demo: db<>fiddle
Related
I have a SQL table with a column called [applied], only one row from all rows can be applied ( have the value of 1) all other rows should have the value 0
Is there a check constraint that i can write to force such a case?
If you use null instead of 0, it will be much easier.
Have a CHECK constraint to make sure the (non-null) value = 1. Also have a UNIQUE constraint to only allow a single value 1.
create table testtable (
id int primary key,
applied int,
constraint applied_unique unique (applied),
constraint applied_eq_1 check (applied = 1)
);
Core ANSI SQL, i.e. expected to work with any database.
Most databases support filtered indexes:
create unique index unq_t_applied on t(applied) where applied = 1;
To know exactly how to write trigger that will help you an info of a database you use is needed.
You wil need a trigger where this will be your test control:
SELECT COUNT(APPLIED)
FROM TEST
WHERE APPLIED = 1
If it is > 0 then do not allow insert else allow.
While this can be done with triggers and constraints, they probably require an index. Instead, consider a join table.
create table things_applied (
id smallint primary key default 1,
thing_id bigint references things(id) not null,
check(id = 1)
);
Because the primary key is unique, there can only ever be one row.
The first is activated with an insert.
insert into things_applied (thing_id) values (1);
Change it by updating the row.
update things_applied set thing_id = 2;
To deactivate completely, delete the row.
delete things_applied;
To find the active row, join with the table.
select t.*
from things t
join things_applied ta on ta.thing_id = t.id
To check if it's active at all, count the rows.
select count(id) as active
from things_applied
Try it.
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 a table with below schema :
CREATE TABLE tbl_name (
id bigserial primary key,
phone_info json
);
Sample json data for phone_info column is given below .
{
"STATUS":{"1010101010":"1","2020202020":"1"},
"1010101010":"OK",
"2020202020":"OK"
}
Now I need to add a check constraint on phone_info column so that all key for "STATUS" ie(1010101010,2020202020) should exist as a (key,value) pair of phone_info column where value would be "OK".
So above sample data would satisfy the check constraint as there are following key value pair exists in phone_info column.
"1010101010":"OK"
"2020202020,":"OK"
I have tried below solution but this has not worked because array_agg function is not supported with check constraints.
ALTER TABLE tbl_name
ADD CONSTRAINT validate_info CHECK ('OK' = ALL(array_agg(phone_info->json_object_keys(phone_info->'STATUS'))) );
Can someone please help me out , Can I write a SQL function and use the function in check constraint?
With something like this I think you'll want an SQL function.
CREATE TABLE tjson AS SELECT '{
"STATUS":{"1010101010":"1","2020202020":"1"},
"1010101010":"OK",
"2020202020":"OK"
}'::json AS col;
perhaps something like:
CREATE OR REPLACE FUNCTION my_json_valid(json) RETURNS boolean AS $$
SELECT bool_and(coalesce($1->>k = 'OK','f'))
FROM json_object_keys($1->'STATUS') k;
$$ LANGUAGE sql IMMUTABLE;
... but remember that while PostgreSQL will let you modify that function, doing so can cause previously valid rows to become invalid in the table. Never modify this function without dropping the constraint then adding it back again.
An, i hope, simple question i sadly can't find the answer to trough googling or RTFMing.
I want to create a column with a default value that is based in the first id of another table.
Something like that, which sadly gives me "ERROR: cannot use subquery in default expression"
ALTER TABLE foobar
ADD COLUMN foo INTEGER DEFAULT (SELECT id FROM blubb LIMIT 1);
The problem is, I can not simply assume that 'blubb' starts at 0 or 1 and I want to put a CONSTRAINT on it later on.
Simple answer: Use a function.
Example:
CREATE TABLE foo (id serial primary key);
CREATE OR REPLACE FUNCTION max_foo() RETURNS int LANGUAGE SQL AS
$$ SELECT max(id) FROM foo; $$;
CREATE TABLE bar(id int not null default max_foo());
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 )