How I can set the default value for an attribute to be the next value of a squeuence
I tried the following :
ALTER TABLE Person ADD COLUMN ccn VARCHAR(254) default (next value for KAP.CCN_SEQ );
And this cause a syntax error
Could you please advice is this doable and if yes what is the correct syntax ?
Thanks in advance.
Your column is of type Varchar - I assume this is a bit unusual for a sequence number. You also need to determine whether you want to create an Identity or a Sequence. For difference between the two and how to create each see: ID vs Sequence in DB2. Some of the points to note are (as quoted from the ref.):
An identity column has the following characteristics:
• An identity column can be defined as part of a table only when the table is created. Once a table is created, you cannot alter it to add an identity column. (However, existing identity column characteristics may be altered.)
• An identity column automatically generates values for a single table.
• When an identity column is defined as GENERATED ALWAYS, the values used are always generated by the database manager. Applications are not allowed to provide their own values during the modification of the contents of the table.
A sequence object has the following characteristics:
• A sequence object is a database object that is not tied to any one table.
• A sequence object generates sequential values that can be used in any SQL statement.
• Since a sequence object can be used by any application, there are two expressions used to control the retrieval of the next value in the specified sequence and the value generated previous to the statement being executed. The PREVVAL expression returns the most recently generated value for the specified sequence for a previous statement within the current session. The NEXTVAL expression returns the next value for the specified sequence. The use of these expressions allows the same value to be used across several SQL statements within several tables.
To create a sequence (example):
CREATE SEQUENCE ccn
START WITH 1
INCREMENT BY 1
NOMAXVALUE
NOCYCLE
CACHE 24
Related
I have a table in postgres that basically just serves to collect multiple object in a bag. Think like a shopping cart. It only has a uuid that is generated automatically.
How can I insert an empty record into such a table?
INSERT INTO cart() values();
Doesn't work
From the fine INSERT manual:
This section covers parameters that may be used when only inserting new rows. [...]
DEFAULT VALUES
All columns will be filled with their default values, as if DEFAULT were explicitly specified for each column. (An OVERRIDING clause is not permitted in this form.)
[...]
DEFAULT
The corresponding column will be filled with its default value. An identity column will be filled with a new value generated by the associated sequence. For a generated column, specifying this is permitted but merely specifies the normal behavior of computing the column from its generation expression.
So you can use DEFAULT as a value to explicitly use the column's default value:
INSERT INTO cart(your_uuid_column) values(default);
or you can say:
INSERT INTO cart default values;
to use defaults for all the columns.
I have a postgres table with two columns (an identificator and a date) that are a composite primary key. I would like to hash the concatenation in another column, generating this value everytime a new record is inserted. For that I'm trying to alter my table in order to create a generated column:
ALTER TABLE my_table ADD COLUMN hash_id_date VARCHAR(50)
GENERATED ALWAYS AS (MD5(my_table.original_id||'-'||my_table.time))
STORED;
This raises me the following error:
ERROR: syntax error at or near "("
LINE 4: GENERATED ALWAYS AS (MD5(my_table.original_id,'-',my_table.t...
^
SQL state: 42601
Character: 178
I'm turning into madness to find where is the syntax error... I've read about STABLE and IMMUTABLE functions and generated columns should always have an IMMUTABLE function as expression. As far as I know MD5 is IMMUTABLE but the error message is not even capable to reach that level.
Any help?
Assuming the basic functionality for calculating the MD5 is common you can create a function for the calculation. Use this function wherever it's needed, including updating your current rows and invoke from a trigger on yo your table. If the particular MD5 calculation is not all that common you can just put the calculation in the trigger function and also use it in a independent update for current rows. See here for example with assumption it is common in your app.
So im working on a database at the moment, and i can see there are loads of sequences. I was wondering how sequences link up to their corresponding column in order to increment the value.
for example if i create a new table with a column names ID how would i apply a sequence to that column.
Typically, sequences are created implicitly. With a serial column or (alternatively) with an IDENTITY column in Postgres 10 or later. Details:
Auto increment table column
Sequences are separate objects internally and can be "owned" by a column, which happens automatically for the above examples. (But you can also have free-standing sequences.) They are incremented with the dedicated function nextval() that is used for the column default of above columns automatically. More sequence manipulation functions in the manual.
Details:
Safely and cleanly rename tables that use serial primary key columns in Postgres?
Or you can use ALTER SEQUENCE to manipulate various properties.
Privileges on sequences have to be changed explicitly for serial columns, while that happens implicitly for the newer IDENTITY columns.
Currently creating my PostgreSQL tables through Postico, and I came across this field for when creating new columns. It is called DEFAULT and its default value is no default. You can select constant, expression, and sequence as options, though.
What exactly do these mean?
The manual on CREATE TABLE:
DEFAULT default_expr
The DEFAULT clause assigns a default data value for the column whose column definition it appears within. The value is any
variable-free expression (subqueries and cross-references to other
columns in the current table are not allowed). The data type of the
default expression must match the data type of the column.
The default expression will be used in any insert operation that does
not specify a value for the column. If there is no default for a
column, then the default is null.
constant and expression should be clear now. sequence is a special feature to make it a serial column:
Creating a PostgreSQL sequence to a field (which is not the ID of the record)
More details on the page #mu provided:
https://www.postgresql.org/docs/current/static/ddl.html
I've created table projects like so:
CREATE TABLE projects (
project_id NUMBER(10,0) GENERATED BY DEFAULT ON NULL AS IDENTITY ,
project_name VARCHAR2(75 CHAR) NOT NULL
Then I've inserted ~150,000 rows while importing data from my old MySQL table. the MySQL had existing id numbers which i need to preserve so I added the id number to the SQL during the insert. Now when I insert new rows into the oracle table, the id is a very low number. Can you tell me how to reset my counter on the project_id column to start at 150,001 so not to mess up any of my existing id numbers? essentially i need the oracle version of:
ALTER TABLE tbl AUTO_INCREMENT = 150001;
Edit: Oracle 12c now supports the identity data type, allowing an auto number primary key that does not require us to create a sequence + insert trigger.
SOLUTION:
after some creative google search terms I was able to find this thread on the oracle docs site. here is the solution for changing the identity's nextval:
ALTER TABLE projects MODIFY project_id GENERATED BY DEFAULT ON NULL AS IDENTITY ( START WITH 150000);
Here is the solution that i found on this oracle thread:. The concept is to alter your identity column rather than adjust the sequence. Actually, the sequences that are automatically created aren't editable or drop-able.
ALTER TABLE projects MODIFY project_id GENERATED BY DEFAULT ON NULL AS IDENTITY ( START WITH 150000);
According to this source, you can do it like this:
ALTER TABLE projects MODIFY project_id
GENERATED BY DEFAULT ON NULL AS IDENTITY (START WITH LIMIT VALUE);
The START WITH LIMIT VALUE clause can only be specified with an ALTER TABLE statement (and by implication against an existing identity column). When this clause is specified, the table will be scanned for the highest value in the PROJECT_ID column and the sequence will commence at this value + 1.
The same is also stated in the oracle thread referenced in OP's own answer:
START WITH LIMIT VALUE, which is specific to identity_options, can only be used with ALTER TABLE MODIFY. If you specify START WITH LIMIT VALUE, then Oracle Database locks the table and finds the maximum identity column value in the table (for increasing sequences) or the minimum identity column value (for decreasing sequences) and assigns the value as the sequence generator's high water mark. The next value returned by the sequence generator will be the high water mark + INCREMENT BY integer for increasing sequences, or the high water mark - INCREMENT BY integer for decreasing sequences.
The following statement creates the sequence customers_seq in the sample schema oe. This sequence could be used to provide customer ID numbers when rows are added to the customers table.
CREATE SEQUENCE customers_seq
START WITH 1000
INCREMENT BY 1
NOCACHE
NOCYCLE;
The first reference to customers_seq.nextval returns 1000. The second returns 1001. Each subsequent reference will return a value 1 greater than the previous reference.
http://docs.oracle.com/cd/B12037_01/server.101/b10759/statements_6014.htm