I have a table with three columns, [Id,QTY,Date]. out of these three, two columns [id and date], should be set as primary keys, because I need to fetch the record one by one, from this table, into a reference.
the data to be inserted into this table is
101,10,NULL
101,20,201220
101,7,201440
102,5,null
102,8,201352
date is in yyyyww format
How do I define two columns as composite primary keys when they have null values, duplicates?
alter table abc add constraint pk primary key (ID, DATE);
if I try to alter the table the error appears
Error report:
SQL Error: ORA-01449: column contains NULL values; cannot alter to NOT NULL
01449. 00000 - "column contains NULL values; cannot alter to NOT NULL"
*Cause:
*Action:
Using table level constraint, you can use this query
alter table your_table add constraint pkc_Name primary key (column1, column2)
but first you need to declare the columns NOT NULL. All parts of a primary key need to be NOT NULL.
The column name of your table is ID and it is still null and non-unique, how is it possible. If it is primary key of other table try adding a surrogate key column for this table and make it primary key.
In case of composite primary key, it should have atleast one not null value(For each row) in the combination of columns. And the combination of column must be unique at all case.
For further details check, http://docs.oracle.com/cd/B10500_01/server.920/a96524/c22integ.htm
Correction - If composite primary key is made up of 3 columns, then no column (among 3) can hold NULL value. And the combination of those 3 columns must be unique.
E.g. (1,2,2)
(1,2,1)
(2,2,1)
(1,2,2) - not valid
Related
I have seen the below create table statement :
create table cruise_orders
(cruise_order_id number,
order_date date,
constraint pk_or_id primary key (cruise_order_id,order_date));
so here the primary_key has two columns. But in case if I try the below statement and try to alter the table cruise_orders and add the column order_date to the primary key pk_or_id it throws an error saying "A table can have only one Primary key".
So how does it works with the first statement ? and why it doesn't work with the second alter statement ?
create table cruise_orders
(cruise_order_id number,
order_date date,
constraint pk_or_id primary key (cruise_order_id));
If you want it so that the cruise_order_id must be unique and, separately, that the order_date must be unique then use two constraints:
CREATE TABLE cruise_orders(
cruise_order_id NUMBER,
order_date DATE,
CONSTRAINT cruise_orders__or_id__pk PRIMARY KEY(cruise_order_id)
);
ALTER TABLE cruise_orders ADD CONSTRAINT cruise_orders__order_date__u UNIQUE(order_date);
If you really do want to have a single constraint with both columns the drop the first constraint and create a second with both columns:
CREATE TABLE cruise_orders(
cruise_order_id NUMBER,
order_date DATE,
CONSTRAINT cruise_orders__or_id__pk PRIMARY KEY(cruise_order_id)
);
ALTER TABLE cruise_orders DROP CONSTRAINT cruise_orders__or_id__pk;
ALTER TABLE cruise_orders ADD CONSTRAINT cruise_orders__coi__od__pk
PRIMARY KEY(cruise_order_id, order_date);
Then you will be able to have duplicate cruise_order_id values provided the order_date is different and vice-versa.
I use oracle and I try to have a recursive relation
CREATE TABLE "EVENT"
(
"EVENT_ID" NUMBER(18) NOT NULL, //primary key
"NAME" VARCHAR(20) NULL,
"RELATED_EVENT_ID" NUMBER(18) NULL //foreign key
);
Event 1 parent is Event 2....
When I try to create this table, I get this error.
ALTER TABLE "EVENT"
ADD CONSTRAINT "FK_RELATED_EVENT_ID"
FOREIGN KEY ("RELATED_EVENT_ID") REFERENCES "EVENT" ("RELATED_EVENT_ID")
Error report -
SQL Error: ORA-02270: no matching unique or primary key for this column-list
02270. 00000 - "no matching unique or primary key for this column-list"
*Cause: A REFERENCES clause in a CREATE/ALTER TABLE statement
gives a column-list for which there is no matching unique or primary
key constraint in the referenced table.
*Action: Find the correct column names using the ALL_CONS_COLUMNS
catalog view
You have two problems:
There is no primary key constraint on this table.
The foreign key constraint you defined has RELATED_EVENT_ID referencing RELATED_EVENT_ID. I suspect that was just a typo.
Change your table definition to:
CREATE TABLE EVENT
(EVENT_ID NUMBER
NOT NULL
CONSTRAINT PK_EVENT
PRIMARY KEY
USING INDEX,
NAME VARCHAR2(20),
RELATED_EVENT_ID NUMBER);
Then add the foreign key constraint as
ALTER TABLE EVENT
ADD CONSTRAINT EVENT_FK1
FOREIGN KEY (RELATED_EVENT_ID) REFERENCES EVENT(EVENT_ID);
db<>fiddle here
EDIT
Note that the better way to handle this is to use a junction table, such as:
CREATE TABLE EVENT_EVENT
(EVENT_ID1 NUMBER
CONSTRAINT EVENT_EVENT_FK1
REFERENCES EVENT(EVENT_ID),
EVENT_ID2 NUMBER
CONSTRAINT EVENT_EVENT_FK2
REFERENCES EVENT(EVENT_ID),
CONSTRAINT PK_EVENT_EVENT
PRIMARY KEY (EVENT_ID1, EVENT_ID2)
USING INDEX);
Then you can drop the RELATED_EVENT_ID column from EVENT as you no longer need it.
According to oracle document :
Foreign key specifies that the values in the column must correspond to values in a
referenced primary key or unique key column or that they are NULL.
In your case, create primary key on column (EVENT_ID) and use it in reference clause as following:
ALTER TABLE "EVENT"
ADD CONSTRAINT "FK_RELATED_EVENT_ID"
FOREIGN KEY ("RELATED_EVENT_ID")
REFERENCES "EVENT" ("EVENT_ID") -- this
Now, use EVENT2's EVENT_ID as RELATED_EVENT_ID in EVENT1 record to make EVENT2 as parent of EVENT1.
Cheers!!
I've been struggling for some time now to figure out a way to create a composite foreign key in liquibase.
I have a table A which has a composite PK, let's say (id1, id2). I'm trying to make another table B, in which the A.PK is mapped as a FK.
I'm using liquibase with YAML and something doesn't seem to add up.
I've tried adding the FK when creating the table (so in the column tag)
- column:
name: id1_id2
type: int
constraints:
nullable: false
foreignKeyName: fk_id1_id2
references: A(id1, id2)
Unfortunately this syntax returns an error:
Caused by: java.sql.SQLSyntaxErrorException: ORA-02256: number of referencing columns must match referenced columns
Another thing that I've tried is creating the table first, with the column for the desired FK and try to add a FK constraint on that column. This doesn't throw any error but it does nothing (also the log for LB says "empty" in the description)
changes:
- addForeignKeyContraint:
baseColumnNames: id1, id2
baseTableName: B
constraintName: fb_id1_id2
referencedColumnNames: id1, id2
referencedTableName: A
Any help would be much appreciated.
Thanks
Have you tried addForeignKeyConstraint? Something like this:
- changeSet:
id: 1
author: you
changes:
- addForeignKeyConstraint:
baseColumnNames: id1, id2
baseTableName: tableB
constraintName: FK_tableB_tableA
referencedColumnNames: id1, id2
referencedTableName: tableA
I don't use Liquibase, but here's how it is supposed to look like, as far as Oracle is concerned: if you want to create a composite foreign key (in the detail table), then it has to reference a composite primary key (in the master table).
Have a look at this example:
SQL> create table master
2 (id_1 number,
3 id_2 number,
4 constraint pk_mas primary key (id_1, id_2));
Table created.
SQL> create table detail
2 (id_det number constraint pk_det primary key,
3 --
4 id_1 number,
5 id_2 number,
6 constraint fk_det_mas foreign key (id_1, id_2) references master (id_1, id_2));
Table created.
SQL>
It just wouldn't work otherwise; that's why you got the error
ORA-02256: number of referencing columns must match referenced columns
because your detail table contained a single column (id1_id2) and tried to reference two columns in table A (id1, id2).
currently i am facing an oracle constraints issue.
After submiting an insert my foreign key constraint(s) won't fire. What it should do is giving two tables the same ID, but unfortunately only the one table with the primary Key is giving an ID. The column with the foreign key in the second table remains null.
For Instance: Insert into table t1 (t1_id,name, dpt) values (value1 (trigger with autoincrement for id), value2, value3); The same procedure is behind table 2, table 3 ... All constraints are written correctly
Table 1 (Emp)
ID Name Department
1 Joe HR
Table 2 (Projects)
ID Project EmpID
1 new (null) -> must be 1
Thank you in advanced.
Constraint: ALTER TABLE "PROJECTS" ADD CONSTRAINT "EMP_FK" FOREIGN KEY ("EMP_ID")
REFERENCES "EMP" ("EMP_ID") ON DELETE CASCADE ENABLE
Trigger: create or replace TRIGGER Projects_TRG BEFORE
INSERT ON Projects FOR EACH ROW BEGIN :NEW.Project_ID := Projects_SEQ.NEXTVAL;
END;
How do i manage to populate the parent id from the parent table into the child table?
Please note that I used different names in my application.
It appears that you've misunderstood the purpose of a foreign key constraint. A foreign key constraint does NOT automatically propagate constraint values from the parent table to the child table. The purpose of the constraint is to ensure that the values of the key column in the child table, when populated, have matching values in the key column of the parent table. Your application is responsible for ensuring that the key column on the child table is populated with the appropriate value. The constraint doesn't do that for you. It's also perfectly legitimate to have a NULL in the key column of the child table, assuming the the column on the child table doesn't have a NOT NULL constraint on it.
According to oracle docs, a null cannot be equal or unequal to any value or to another null
This is evident in case of a uniqueness constraint on any column. But the behaviour is different if the uniqueness constraint in on multiple columns. eg:
CREATE TABLE table1 (
col1 NUMBER(2),
col2 NUMBER(2),
CONSTRAINT uniq_col1_col2 UNIQUE (col1, col2)
);
INSERT INTO table1 VALUES (1, NULL);
INSERT INTO table1 VALUES (1, NULL);
# ORA-00001: unique constraint (XYZ.UNIQ_COL1_COL2) violated
Why is this so? And how can I specify the constraint to ignore nulls?
EDIT
More specifically, if rows (null), (null) are unique, why are (1,null), (1,null) not unique? What is the rationale behind this?
That's what the documentation says (emphasis added):
To satisfy a unique constraint, no two rows in the table can have the same value for the unique key. However, the unique key made up of a single column can contain nulls. To satisfy a composite unique key, no two rows in the table or view can have the same combination of values in the key columns. Any row that contains nulls in all key columns automatically satisfies the constraint. However, two rows that contain nulls for one or more key columns and the same combination of values for the other key columns violate the constraint.
It's doing what it's supposed to do. With your two sample inserts, both (potential) rows contain null in one key column and the same value (1) in the other key column, so the constraint is violated.
Nothing else would really make sense; allowing both inserts to go ahead would leave you with two indistinguishable rows, in key terms anyway.
You asked:
More specifically, if rows (null), (null) are unique, why are (1,null), (1,null) not unique? What is the rationale behind this?
Because there is no other key column to enforce uniqueness.
As you said, null isn't equal to or not equal to anything. If your unique key was only on col1 and you had two rows with it set to null, which is allowed, then querying where col1 is null would find both - which is OK because is null isn't about equality. You can say that both rows matched the condition, but not that they are equal to null. With your two-column key the equivalent would be where col1 = 1 and col2 is null. Now equality does come into play.
In both cases the nulls are ignored, and whatever is left still has to be unique. With a single-column key there is nothing else to enforce uniqueness. With the two-column key if col2 is null then col1 is still there to be compared, and that on its own has to be unique, effectively.
You're also allowed to do:
INSERT INTO table1 VALUES (null, null);
INSERT INTO table1 VALUES (null, null);
The same thing applies; they nulls are effectively ignored, but now - as with the single-column-key - there is nothing left to enforce uniqueness against.
If you really want a constraint that ignores nulls and only prevents insert of complete duplicate keys then you can use a function-based unique index that only holds keys that are totally non-null:
create unique index uniq_col1_col2 on table1
( case when col1 is not null and col2 is not null then col1 end
, case when col1 is not null and col2 is not null then col2 end
);