I need to drop a constraint (say, foreign key). But the table, the constraint on it, or both, may not exist.
I tried:
ALTER TABLE IF EXISTS Table1 - invalid syntax
ALTER TABLE Table1 DROP CONSTRAINT IF EXISTS Constraint - fails if Table1 is missing
funky CASE WHEN stuff like
select CASE (select count(*)
from INFORMATION_SCHEMA.CONSTRAINTS
where CONSTRAINT_SCHEMA = 'DBO'
and CONSTRAINT_NAME = upper('FK_Table1_Col1_Table2_Col2'))
WHEN 1 THEN 'select 5'
end
In MS SQL for example you have all the IF EXISTS clauses allowing you to branch script easily. Not so with H2, it would seem. There should be some way to make it work similar to my attempt with CASE WHEN, no ?
If possible, I want to avoid writing Java code in the sql file.
Related
Need to add two following insert statements:
insert into table1(schema, table_name, table_alias)
values ('ref_owner','test_table_1','tb1');
insert into table1(schema, table_name, table_alias)
values ('dba_owner','test_table_2','tb2');
Question is how can I make those two insert statements re-runnable meaning, if those two insert statement are compiled again, it should throw row exists error or something along those lines...?
Additional notes:
1. I've seen examples of Merge in Oracle however, thats only when you're using two tables to match records. In this case im only using a single table.
2. The table does not have any primary, unique or foreign keys - only check constraints on one of the columns.
Any help is highly appreciated.
You can use a MERGE statement, as follows:
MERGE into table1 t1
USING (SELECT 'ref_owner' AS SCHEMA_NAME, 'test_table_1' AS TABLE_NAME, 'tb1' AS ALIAS_NAME FROM DUAL
UNION ALL
SELECT 'dba_owner', 'test_table_2', 'tb2' FROM DUAL) d
ON (t1.SCHEMA = d.SCHEMA_NAME AND
t1.TABLE_NAME = d.TABLE_NAME)
WHEN NOT MATCHED THEN
INSERT (SCHEMA, TABLE_NAME, TABLE_ALIAS)
VALUES (d.SCHEMA_NAME, d.TABLE_NAME, d.ALIAS_NAME)
Best of luck.
You should have a primary key, especially when you want to check for duplicate records and data integrity.
Provide a primary key for your table, or, if you somehow do not want to do that, create a unique constraint for all of the columns in the table, so no duplicate rows are possible.
I want to ask a very basic question here.
We may/may not name a constraint while creating a table or after creating the table.
Suppose I chose not to name the foreign key constraint.
The table is having no records.
Can I delete the foreign key name without naming it.
I know how to get name of foreign key and then delete using it like
alter table my_table drop constraint fk_name;
but I want to delete/drop the foreign key constraint without mentioning its name.
Is there anyway to do it?
but i want to delete/drop the foreign key constraint without mentioning its name.
That's not possible. The dropping a foreign key constraint requires a name. However you can find out the system generated name:
select constraint_name
from user_constraints
where table_name = 'MY_TABLE'
and constraint_type = 'R';
Will show you all foreign keys defined on the table MY_TABLE. Using that statement you can even generate the necessary DDL statement:
select 'alter table "'||table_name||'" drop constraint "'||constraint_name||'";'
from user_constraints
where table_name = 'MY_TABLE'
and constraint_type = 'R';
Save the output of that select into a file and you have the statement(s) to drop all foreign keys from that table.
I have a oracle query as -
occupation varchar2(50) CHECK(occupation IN ('student','govt_service','private','business')));
now i need to remove the check constraint so i use the following query-
ALTER TABLE registration drop constraint occupation;
but since i haven't defined the constraint name it says invalid constraint name. Is there any way to delete the constraint ? I guess i can alter the table and add the name of the constraint, then delete it but is there any other way ?
run this query:
select * from all_constraints where table_name = 'REGISTRATION';
And you'll find the constraint name.
EDIT: I also recommend you to have a table Occupations and replace the current constraint with a foreign key. (If you are already want to do this, pls apologize me ). Further, normalising, the Occupations may have IDs and and the foreign should be defined on these ids.
Try querying USER_CONSTRAINTS table for CONSTRAINT_NAME, it must have generated a system name for the constraint you have created.
select * from USER_CONSTRAINTS
where owner='<your_schema>' and CONSTRAINT_TYPE='C';
ALTER TABLE testTable ADD column1 NUMBER(1) DEFAULT 0 NOT NULL AFTER column2;
Why can't I use mySql syntax in Oracle too? The above command works in MySql. Can you give me an equivalent that works?
Error report:
SQL Error: ORA-01735: invalid ALTER TABLE option
01735. 00000 - "invalid ALTER TABLE option"
I am asking if there is any way to use after clause in Oracle command that I provided?
Because SQL is a relational algebra. It doesn't care one bit about "where" columns are located within a table, only that they exist.
To get it to work in Oracle, just get rid of the after clause. The Oracle documentation for alter table is here but it boils down to:
alter table testTable
add ( column1 number(1) default 0 not null )
There is no after clause for the alter table command.
Oracle does not support adding columns in the middle of a table, only adding them to the end. Your database design and app functionality should not depend on the order of columns in the database schema. You can always specify an order in your select statement, after all.
However if for some reason you simply must have a new column in the middle of your table there is a work around.
CREATE TABLE tab1New AS SELECT 0 AS col1, col1 AS col2 FROM tab1;
DROP TABLE tab1 PURGE;
RENAME tan1New to tab1;
Where the SELECT 0 AS col1 is your new column and then you specify other columns as needed from your original table. Put the SELECT 0 AS col1 at the appropriate place in the order you want.
Afterwards you may want to run an alter table statement on the column to make sure it's the data type you desire.
Try this :
ALTER TABLE testTable ADD column1 NUMBER(1) DEFAULT 0 NOT NULL
I have a database which has a NOT NULL constraint on a field, and I want to remove this constraint. The complicating factor is that this constraint has a system-defined name, and that constraint's name differs between the production server, integration server, and the various developer databases. Our current process is to check in change scripts, and an automated task executes the appropriate queries through sqlplus against the target database, so I'd prefer a solution that could just be sent straight into sqlplus.
On my own database, the SQL to drop this would be:
alter table MYTABLE drop constraint SYS_C0044566
I can see the constraint when I query the all_constraints view:
select * from all_constraints where table_name = 'MYTABLE'
but I am not sure how to work with the SEARCH_CONDITION's LONG data type or how best to dynamically delete the looked-up constraint even after I know its name.
So, how can I create a change script that can drop this constraint based on what it is, rather than what its name is?
EDIT:
#Allan's answer is a good one, but I am concerned (in my lack of Oracle expertise) that it may not be universally true that any constraint that might have a system-generated name will have associated with it a way to remove the constraint without having to know its name. Is it true that there will always be a way to avoid having to know a system-named constraint's name when logically dropping that constraint?
alter table MYTABLE modify (MYCOLUMN null);
In Oracle, not null constraints are created automatically when not null is specified for a column. Likewise, they are dropped automatically when the column is changed to allow nulls.
Clarifying the revised question: This solution only applies to constraints created for "not null" columns. If you specify "Primary Key" or a check constraint in the column definition without naming it, you'll end up with a system-generated name for the constraint (and the index, for the primary key). In those cases, you'd need to know the name to drop it. The best advice there is to avoid the scenario by making sure you specify a name for all constraints other than "not null". If you find yourself in the situation where you need to drop one of these constraints generically, you'll probably need to resort to PL/SQL and the data-definition tables.
Try:
alter table <your table> modify <column name> null;
Just remember, if the field you want to make nullable is part of a primary key, you can't.
Primary Keys cannot have null fields.
To discover any constraints used, use the code below:
-- Set the long data type for display purposes to 500000.
SET LONG 500000
-- Define a session scope variable.
VARIABLE output CLOB
-- Query the table definition through the <code>DBMS_METADATA</code> package.
SELECT dbms_metadata.get_ddl('TABLE','[Table Described]') INTO :output FROM dual;
This essentially shows a create statement for how the referenced table is made. By knowing how the table is created, you can see all of the table constraints.
Answer taken from Michael McLaughlin's blog: http://michaelmclaughlin.info/db1/lesson-5-querying-data/lab-5-querying-data/ From his Database Design I class.
I was facing the same problem trying to get around a custom check constraint that I needed to updated to allow different values. Problem is that ALL_CONSTRAINTS does't have a way to tell which column the constraint(s) are applied to. The way I managed to do it is by querying ALL_CONS_COLUMNS instead, then dropping each of the constraints by their name and recreate it.
select constraint_name
from all_cons_columns
where table_name = [TABLE_NAME]
and column_name = [COLUMN_NAME];
Something like that happened to me when I made copies of structures to temporary tables, so I removed the not null.
DECLARE
CURSOR cur_temp_not_null IS
SELECT table_name, constraint_name FROM all_constraints WHERE table_name LIKE 'TEMP_%' AND owner='myUSUARIO';
V_sql VARCHAR2(200);
BEGIN
FOR c_not_null IN cur_temp_not_null
LOOP
v_sql :='ALTER TABLE ' || c_not_null.table_name || ' DROP CONSTRAINT '|| c_not_null.constraint_name;
EXECUTE IMMEDIATE v_sql;
END LOOP;
END;
If constraint on column STATUS was created without a name during creating a table, Oracle will assign a random name for it. Unfortunately, we cannot modify the constraint directly.
Steps involved of dropping unnamed constraint linked to column STATUS
Duplicate STATUS field into a new field STATUS2
Define CHECK constraints on STATUS2
Migrate data from STATUS into STATUS2
Drop STATUS column
Rename STATUS2 to STATUS
ALTER TABLE MY_TABLE ADD STATUS2 NVARCHAR2(10) DEFAULT 'OPEN';
ALTER TABLE MY_TABLE ADD CONSTRAINT MY_TABLE_CHECK_STATUS CHECK (STATUS2 IN ('OPEN', 'CLOSED'));
UPDATE MY_TABLE SET STATUS2 = STATUS;
ALTER TABLE MY_TABLE DROP COLUMN STATUS;
ALTER TABLE MY_TABLE RENAME COLUMN STATUS2 TO STATUS;