I am attempting to add a constraint to a DB2 database that will check three columns. I am using a table that is an invoice table that includes start date end date quantity item price etc. for each line item on an invoice. I want to prevent allowing start and end date from being null when a column linestatus = RELELASED. Here is the alter statement that I have so far. My question is why won't this work? I have verified that this table does not have any current instances of all three of these checks.
alter table pluspgbtrans
add constraint start_end_notnull
Check (eip_linestatus = 'RELEASED' AND eip_endate is not null AND eip_startdate is not null)
Your SQL statement is valid.
However, your logic has an error: this check does not apply only if eip_linestatus = 'RELEASED'.
As written, your constraint is asserting that all rows must have eip_linestatus = 'RELEASED' AND eip_endate is not null AND eip_startdate is not null.
So, if any rows in your table have eip_linestatus with a value of anything other than RELEASED, you'll get the SQL0544N error when you try to add the constraint.
To create the constraint you're looking for, you need to handle the other state(s) for eip_linestatus. I can't guess what they are, so here's a potential generic option:
alter table pluspgbtrans
add constraint start_end_notnull check (
(eip_linestatus <> 'RELEASED')
OR
(
eip_linestatus = 'RELEASED'
AND eip_endate is not null
AND eip_startdate is not null
)
);
Related
I have a column 'name' in student table. I need to add NOT NULL constraint on this column. But I get SQL error saying cannot add null constraint since the existing rows in the table has null values in the column. How would I add a null constraint along with default value in a single alter statement. Below is my query.
alter table Student alter column name nvarchar NOT NULL;
SQL Server does not make this easy. I think the only way is to set the existing values to the default that you want. Then change the column to have a default value and not null:
-- Get rid of the existing `NULL` values
update students set name = '' where name is null;
-- Add the NOT NULL constraint
alter table students
alter column name varchar(255) not null;
-- Add a default value
alter table students
add constraint df_t_name default '' for name ;
Here is what it looks like in practice.
But I get SQL error saying cannot add null constraint since the existing rows in the table has null values in the column.
Have you tried overwriting the existing NULL values?
You can't have a constraint on a column when existing values would violate that constraint. You need to make your table compliant first.
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 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 am getting this error
ORA-02438: Column check constraint cannot reference other columns
when I am performing this query
alter table Issue
modify Issue_Date not null check (Issue_Date <= sys_date);
as well as I have to add this condition also (issue_date<return_date);
and when I tried this
alter table Issue
add constraint ck_Issue_Date not null check (Issue_Date <= sys_date);
ERROR ORA-00904: : invalid identifier
I suspect you are wanting to reference the Oracle SYSDATE function, not a column named sys_date.
Unfortunately, the conditions in a CHECK CONSTRAINT cannot reference the SYSDATE function.
To get the database enforce this type of restriction on the value of a column, that would require a TRIGGER.
For example, something like this:
CREATE OR REPLACE TRIGGER trg_issue_issue_date_biu
BEFORE INSERT OR UPDATE ON Issue
FOR EACH ROW
BEGIN
IF (NEW.Issue_Date <= SYSDATE) THEN
NULL;
ELSE
RAISE_APPLICATION_ERROR(-20000, 'Invalid: Issue_Date is NULL or >SYSDATE');
END IF;
END;
You tried to mix up inline column level constraint and table level constraint (for more than 1 column). Please simply split them on 2 statements:
alter table Issue
modify Issue_Date not null;
alter table Issue
add constraint ck_Issue_Date check (Issue_Date <= sys_date);
alter table Issue
add constraint ck_Issue_Date2 check (issue_date<return_date);
I want to add a new column to an existing table.
I need it to emulate the enum type (in the way possible in SQL Server; with value constraints, that is).
The following doesn't work:
ALTER TABLE orders ADD [sent_to_panel] NVARCHAR(16) NULL;
ALTER TABLE orders WITH CHECK ADD CONSTRAINT [CK_orders] CHECK (([sent_to_panel]='invalidated' OR [sent_to_panel]='not_sent' OR [sent_to_panel]='sent'));
ALTER TABLE orders ADD CONSTRAINT [DF_orders_sent_to_panel] DEFAULT (N'not_sent') FOR [sent_to_panel];
ALTER TABLE orders CHECK CONSTRAINT [CK_orders];
I'm getting an error:
Msg 207, Level 16, State 1, Line 2
Invalid column name 'sent_to_panel'.
If I execute the first command on its own, though:
ALTER TABLE orders ADD [sent_to_panel] NVARCHAR(16) NULL;
The rest goes through.
So I suppose the problem is that the column isn't actually added yet (and thus not recognized by ADD CONSTRAINT) when trying to get it all done in one go.
The question is: how to make the script work properly?
CREATE TABLE a (
b int
);
ALTER TABLE a
ADD c nvarchar(16) NULL
, CONSTRAINT check_this CHECK (c IN ('invalidated', 'not_sent', 'sent'))
, CONSTRAINT defaultify DEFAULT ('not_sent') FOR c
;
ALTER TABLE a
CHECK CONSTRAINT check_this
;
DROP TABLE a;