1. is that you mean, You can set primary key constraint, or Not null constraint on the column, n A NOT NULL constraint prohibits a database value from being null. insert into test (col1, col2) values (2, null) To modify a column of a table, you need to specify the column name, table name, and action that you want to perform. Shall I … A default value is the value that is inserted into a column if no other value is specified. 15. Alter table to modify default value of column (3) I have a requirement where we need to modify a column's default value in database table. This Oracle ALTER TABLE example will rename the customers table to contacts. SQL> alter table BOOKS_MASTER modify BCOST default 1000; Table altered. You simply alter the column as: SQL> create table tab1 (col1 number, col2 number); Table created. CREATE TABLE members( member_id NUMBER GENERATED BY DEFAULT AS IDENTITY, first_name VARCHAR2 (50), last_name VARCHAR2 (50), PRIMARY KEY (member_id) ); The following statement adds a new column named birth_date to the members table: ALTER TABLE members ADD birth_date DATE … Typically, you create a primary key for a table when you create that table. The table is already existing and does have a default binding value associated with a column which I want to change and it does not have any constraint on it, so when I use the below code: ALTER TABLE [dbo]. Find out how to change a column's default value at a … When you add a DEFAULT value to a column which is Nullable, Oracle recognizes a NULL as a legitimate existing value and will not make any updates. Oracle MODIFY column default value. A table column) or it may be deeply nested inside a hierarchical table schema. The table is already an existing table in database and currently the default value of the column is NULL. For example , suppose you create an NDB Cluster Disk Data table with two columns, using this CREATE TABLE statement: mysql> CREATE TABLE t3 (c1 INT, c2 INT)-> TABLESPACE ts_1 STORAGE DISK ENGINE NDB; Query OK, 0 rows affected (1.34 sec) To change column … A default value is not a constraint in Oracle. Suppose, we want to add international code to the phone numbers. For example, the following statement checks whether the members table has the first_name column. The city column will be set to a varchar2(75) data type, its default value will be set to 'Seattle', and the column will not allow null values. The default value can be literal value, an expression, or a SQL Function, such as SYSDATE. The customer_name column will be set to a varchar2(100) data type and not allow null values. The ALTER TABLE MODIFY COLUMN (or ALTER TABLE ALTER COLUMN) command allows you to make the following kinds of changes: Change the data type of an existing column; Add constraints to existing columns (such as NOT NULL) Set the default value; To rename a column, you use the ALTER TABLE RENAME COLUMN command, which is detailed below. Hi, Mandatory column means it should always have value? n A primary key … In a more complicated example, you could use the ALTER TABLE statement to add a default value as well as modify the column definition: In this example, the ALTER TABLE statement would modify the column called city to be a data type of varchar2(75), the default value would be set to 'Seattle' and the column would be set to not allow null values. The addColumn Change Type adds a new column to an existing table. Fill data into new added table column: 6.3.11. The field to add may be a top-level field (i.e. ALTER function example. Db2 allows you to change the data type of a column, adjust the column length, and change the default value to a new one. The example also shows how to change the SG attributes from their original definitions, START WITH , INCREMENT BY , MAXVALUE , CACHE and CYCLE . The ALTER FUNCTION statement explicitly recompile a standalone function. Oracle allows you to perform many actions but the following are the main ones: To modify multiple columns, you use the following syntax: First, create a new table named accounts for the demonstration: Second, insert some rows into the accounts table: Third, verify the insert operation by using the following SELECT statement: In Oracle Database 12c, you can define table columns as invisible or visible. For example, we try to shorten the size of the phone column down to 12 characters: Oracle Database issued the following error: To fix this, first, we should remove the international code from the phone numbers: The REPLACE() function replaces a substring by a new substring. Using default values on database columns helps to insulate database design issues from application code. You can only insert into the REAL columns using an insert statement. Before doing it, we must widen the size of the phone column by using the following statement: The following statement verifies the update: To shorten the size of a column, you make sure that all data in the column fits the new size. Oracle alter table change column datatype Oracle Database Tips by Donald Burleson . In a more complicated example, you could use the ALTER TABLE statement to add a new column that also has a default value: In this example, the column called city has been added to the customers table with a data type of varchar2(40) and a default value of 'Seattle'. I have a table called cust_file, his table consists of a lot of columns (one of these columns called cus_tax) and have a lot of data,I use oracle 11g, I want to change the default value of the column cus_tax to be equal 1, I wrote Oracle alter table modify column explained by practical examples oracle alter table modify column explained by practical examples oracle alter table modify column explained by practical examples db2 alter table column by practical examples. To modify a column of a table, you need to specify the column name, table … SQL DEFAULT on CREATE TABLE. This Oracle ALTER TABLE example will modify both the customer_name and city columns. Alter table to add primary key across more than one columns: 6.3.16. Removing column defaults Is there any possible way to remove a default value from a column once it has been created? This Oracle ALTER TABLE example will rename the column called customer_name to cname. Alter Table - add Default value for a COLUMN type BLOB. Dropping a Column: 6.3.17. 1) Modifying the length & data type of column examples . 1. Changing the data type “varchar'' of a column to ”DATE" in SQL/ORACLE. Hot Network Questions Why is it "she really done me"? The default value is only used when the column is not referenced by the insert. We’ll use the orders table created in the ALTER TABLE ADD COLUMN tutorial for the demonstration. Copyright © 2020 Oracle Tutorial. The Oracle ALTER TABLE statement is used to add, modify, or drop/delete columns in a table. n A unique constraint prohibits multiple rows from having the same value in the same column or combination of columns but allows some values to be null. Sometimes, ALTER TABLE on the table being used in function will cause the function becomes INVALID, we need to recompile (alter function) it to make it VALID again. CREATE TABLE … Oracle MODIFY column default value. This Oracle ALTER TABLE example will add two columns, customer_name as a varchar2(45) field and city as a varchar2(40) field with a default value of 'Seattle' to the customers table. As an example: The EMP table is created with a virtual column named TTL_COMP and is calculated from the sal and comm values in each row. To fix this, we update the values for the email column first: Note that the LOWER() function converts a string to lowercase. To change the definition of a column in a table, you use the ALTER TABLE MODIFY column syntax as follows: ALTER TABLE table_name MODIFY column_name action ; The statement is straightforward. Adding a field does not affect the existing rows in the table. First, the following CREATE TABLE statement creates a new table named parts: CREATE TABLE parts ( part_id NUMBER GENERATED BY DEFAULT AS IDENTITY, part_name VARCHAR (50) NOT NULL, lead_time NUMBER (2, 0) NOT NULL, … SQL> alter table BOOKS_MASTER modify BCOST default 1000; Table altered. To change the basic property of an IDENTITY column being GENERATED ALWAYS to GENERATED BY DEFAULT, see the next ALTER TABLE example. Here are some examples of Oracle "alter table" syntax to modify data columns and note that you can add constraints like NOT NULL: ALTER TABLE customer MODIFY ( cust_name varchar2(100) not null, cust_hair_color varchar2(20) ); We can also use Oracle "alter table" syntax in dynamic PL/SQL to modify data columns. Alter table to add new constraint for new added column: 6.3.13. In the Oracle database, if we want to insert a default value into a table column then we are using the DEFAULT Clause. Pics of : Alter Table Modify Column Oracle Default Value READ Insert Data From One Table To Another In Sql Server 2008 Creating And Managing Tables In Oracle Dhiraj Ar Jha Never 2. TechOnTheNet.com requires javascript to work properly. SQL> alter table tab1 modify (col2 default 1); Table altered. ALTER TABLE operations permitted for generated columns are ADD, MODIFY, and CHANGE. Whats people lookup in this blog: Oracle Alter Table Modify Column Default Value Example In this tutorial, you have learned how to use the Oracle ALTER TABLE MODIFY column statement to change the definition of existing columns in a table. ALTER TABLE . Generated columns can be added. How to modify default value? For example in EMP table suppose most of the employees are from Hyderabad, then you can put this as default value for CITY column. To add a column to an existing database table with a default value, we can use: ALTER TABLE [dbo.table_name] ADD [Column_Name] BIT NOT NULL Default ( 0 ) Here is another way to add a column to an existing database table with a default value. The following Oracle ALTER TABLE statement would modify the customer_name and state columns accordingly in the customers table: Based on the employees table below, drop the salary column. The table is already an existing table in database and currently the default value of the column is NULL. if we have to modify the default value of the column. The DEFAULT keyword provides a default value to a column when the Oracle INSERT INTO statement does not provide a specific value. if we have to modify the default value of the column. Up ALTER TABLE Statement ; Next ALTER TABLE Examples ; 13.1.9.2 ALTER TABLE and Generated Columns . What is ALTER table ADD column Oracle DEFAULT value? This Oracle ALTER TABLE example will modify the column called customer_name to be a data type of varchar2(100) and force the column to not allow null values. The DEFAULT keyword provides a default value to a column when the Oracle INSERT INTO statement does not provide a specific value. In addition, you can add a primary key to a table after the fact by using the ALTER TABLE statement. To RENAME A TABLE, the Oracle ALTER TABLE syntax is: Let's look at an example that shows how to rename a table in Oracle using the ALTER TABLE statement. Obviously this c The following Oracle ALTER TABLE statement would add a bonus column to the employees table: Based on the customers table below, add two columns - one column called contact_name that is a varchar2(50) datatype and one column called last_contacted that is a date datatype. CACHE For data that is accessed frequently, this clause indicates that the blocks retrieved for this table are placed at the most recently used end of the least recently used (LRU) list in the buffer cache when a full table scan is performed. To MODIFY A COLUMN in an existing table, the Oracle ALTER TABLE syntax is: Let's look at an example that shows how to modify a column in an Oracle table using the ALTER TABLE statement. For complete tips on Oracle alter table syntax, see the book "Easy Oracle Jumpstart". Learn oracle - oracle tutorial - Oracle alter table with modify not null - oracle examples - oracle programs MODIFY COLUMN OF A TABLE: To modify the column in a table… For Oracle and MySQL, the SQL syntax for ALTER TABLE Modify Column is, ALTER TABLE "table_name" MODIFY "column_name" "New Data Type"; For SQL Server, the syntax is, ALTER TABLE "table_name" ALTER COLUMN "column_name" "New Data Type"; Let's look at the example. The following Oracle ALTER TABLE statement would drop the salary column from the employees table: Based on the departments table below, rename the department_name column to dept_name. Sometimes, you may want to modify column definition to cope with the new business requirements such as extend the maximum length of a column or changing the default value of a column to a new one. In the Oracle database, if we want to insert a default value into a table column then we are using the DEFAULT Clause. The following Oracle ALTER TABLE statement would change the datatype for the employee_name column to varchar2(75): Based on the customers table below, change the customer_name column to NOT allow null values and change the state column to a varchar2(2) datatype. Removing column defaults Is there any possible way to remove a default value from a column once it has been created? You can specify a default value for a new column. The following example uses the ALTER TABLE ALTER COLUMN statement to change … This Oracle tutorial explains how to use the Oracle ALTER TABLE statement to add a column, modify a column, drop a column, rename a column or rename a table (with syntax, examples and practice exercises). The following Oracle ALTER TABLE statement would add the contact_name and last_contacted columns to the customers table: Based on the employees table below, change the employee_name column to a varchar2(75) datatype. Ask Question Asked 9 years, 5 ... How to alter a column and change the default value? Add a column to a table ALTER TABLE STAFF_OPTIONS ADD SO_INSURANCE_PROVIDER Varchar2(35); Add a default value to a column ALTER TABLE STAFF_OPTIONS MODIFY SO_INSURANCE_PROVIDER Varchar2(35) DEFAULT 'ABC Ins'; Add two columns to a table and remove a constraint ALTER TABLE STAFF_OPTIONS ADD (SO_STAFF_ID INT, SO_PENSION_ID … To change the definition of a column in a table, you use the ALTER TABLE MODIFY column syntax as follows: The statement is straightforward. Oracle PRIMARY KEY constraint examples. Let's look at an example that shows how to modify a column in an Oracle table using the ALTER TABLE statement. Sometimes we need to change the data type of a column. Adding column to 11 billion rows table with value 0 as default, then in future application guys will change it to either 1 or 0 as per customer data. The DEFAULT constraint is used to provide a default value for a column. Oracle ALTER TABLE ADD column examples. Oracle UPDATE examples. Calling PL/SQL Stored Functions in Python, Deleting Data From Oracle Database in Python. So either can increase the length or update that column. To rename a column in oracle we have to use rename column statement You have to use rename column statement along with alter table statement The RENAME COLUMN statement allows us to rename an existing column in an existing table in any schema (except the schema SYS). Column default values in Oracle 12C Hi Tom,We are converting oracle tables as partition tables.To do this we are using ORACLE Exchange Partition.Database version 12C.Steps we are following.1.Original table --existing table create table tab1(col1 integer, col2 varchar2(100)); 2.Cur To DROP A COLUMN in an existing table, the Oracle ALTER TABLE syntax is: Let's look at an example that shows how to drop a column in an Oracle table using the ALTER TABLE statement. ... My SQL / SQL Server / Oracle / MS Access: CREATE TABLE Persons ( ID int NOT NULL, LastName varchar(255) NOT NULL, ... ALTER TABLE Persons MODIFY City DEFAULT 'Sandnes'; DROP a DEFAULT Constraint. The ALTER TABLE MODIFY COLUMN (or ALTER TABLE ALTER COLUMN) command allows you to make the following kinds of changes: Change the data type of an existing column; Add constraints to existing columns (such as NOT NULL) Set the default value; To rename a column, you use the ALTER TABLE RENAME COLUMN command, which is detailed below. The Oracle ALTER TABLE statement is also used to rename a table. Oracle Database assigns this value to the column ... Each of the parts of this clause can be specified only once in the statement and cannot be mixed with any other ALTER TABLE clauses. BEGIN SQL_STRING := 'ALTER TABLE '||:TABLE_NAME||' MODIFY … An example of this feature at work can be seen in 11g Enhancement for ALTER TABLE .. ADD COLUMN Functionality and some bugs regarding sysdate, as pointed out in the comments. I want to know the consequences of adding a DEFAULT value to an existing column in a table. SQL> select * from user_constraints; no rows selected SQL> insert into tab1 (col1) values (0); 1 row created. Running the addColumn Change Type. Changing the Default Value of a Column: 6.3.12. For example in EMP table suppose most of the employees are from Hyderabad, then you can put this as default value for CITY column. First thought of adding it and updating later with value 0..but that takes huge time with most of the methods..so decided to leverage on this great feature. ALTER TABLE to DISABLE a CONSTRAINT: 6.3.14. I still get the below error: Let’s create a table named members for the demonstration. What is ALTER table ADD column Oracle DEFAULT value? You can use DEFAULT default-value to change a column default. First, we will create table test_alter, function get_max_amount.In this function, we are using ‘amount’ column of test_alter. Summary: in this tutorial, you will learn how to use the SQL Server ALTER TABLE ALTER COLUMN statement to modify a column of a table.. SQL Server allows you to perform the following changes to an existing column of a table: Modify the data type; Change the size; Add a NOT NULL constraint; Modify column’s data type The default value will be added to all new records IF no other value is specified. You can also specify the DEFAULT value for columns i.e. The default value can be literal value, an expression, or a SQL Function, such as SYSDATE. Here are some examples of Oracle "alter table" syntax to add data columns. Oracle 11g has improved this behaviour by storing the default value in the metadata and making the column addition instantaneous. And then shorten the size of the phone column: Suppose, we the full name in the following format: To do this, we can change the expression of the virtual column full_name as follows: The following statement verifies the modification: Let’s add a new column named status to the accounts table with default value 1. You can typically use the addColumn Change Type when you want to add a new column and deploy it to the table in your database. Insert values for both columns; null for the second column. SQL> alter table Books_master modify title VARCHAR2(20); Table altered. Recently, I have stumble upon an Arup Nanda article on it where he states the following'When a user selects the column for an existing record, Oracle gets the fact about the default value from the data dictionary and return Change Default Value Of Certain Column In A Table In Oracle 11g Aug 18, 2013. The sequence should already exist in the d… Inserting a value for just one of the columns - what will happen to the second column for that row? Summary: in this tutorial, you will learn how to use the SQL Server ALTER TABLE ALTER COLUMN statement to modify a column of a table.. SQL Server allows you to perform the following changes to an existing column of a table: Modify the data type; Change the size; Add a NOT NULL constraint; Modify column’s data type This Oracle ALTER TABLE example will drop the column called customer_name from the table called customers. MODIFY [COLUMN]. How to add default value in the column of the Oracle database table? Using default values on database columns helps to insulate database design issues from application code. If you omit it, the UPDATE statement will update all rows of the table. To change a column from invisible to visible, you use the statement below: The following statement changes the email column to accept non-null values: However, Oracle issued the following error: Because when you changed a column from nullable to non-nullable, you must ensure that the existing data meets the new constraint. The following Oracle ALTER TABLE statement would rename the departments table to depts: Based on the employees table below, add a column called bonus that is a number(6) datatype. Add a column to a table ALTER TABLE STAFF_OPTIONS ADD SO_INSURANCE_PROVIDER Varchar2(35); Add a default value to a column ALTER TABLE STAFF_OPTIONS MODIFY SO_INSURANCE_PROVIDER Varchar2(35) DEFAULT 'ABC Ins'; Add two columns to a table and remove a constraint ALTER TABLE STAFF_OPTIONS ADD (SO_STAFF_ID INT, SO_PENSION_ID … Db2 ALTER TABLE ALTER COLUMN examples. To ADD MULTIPLE COLUMNS to an existing table, the Oracle ALTER TABLE syntax is: Let's look at an example that shows how to add multiple columns in an Oracle table using the ALTER TABLE statement. Once you executed the statement, the values in the status column are set to 1 for all existing rows in the accounts table. (modify_table_default_attrs::=, alter ... Use the DEFAULT clause to specify a default for a new column or a new default for an existing column. Copyright © 2003-2020 TechOnTheNet.com. In an ALTER TABLE statement, the existing value is not changed. Creating a primary key that consists of one column. Oracle alter table change column datatype. Introduction to Db2 ALTER TABLE ALTER COLUMN statement. You should also consider using Identity columns for this purpose.In the following example you can see the effect of specifying a sequence as the default value for a column. SQL > SQL ALTER TABLE > Modify Column Syntax. Oracle Rename table query example: Alter table rename column in oracle table query Oracle Rename Column table syntax: To rename a column in oracle we have to use rename column statement; You have to use rename column statement along with alter table statement; The RENAME COLUMN statement allows us to rename an existing column in an existing table in any schema (except the schema SYS). The following Oracle ALTER TABLE statement would rename the department_name column to dept_name in the departments table: Home | About Us | Contact Us | Testimonials | Donate. How to modify default value? Use the ALTER TABLE statement to alter the definition of a nonpartitioned table, a partitioned table, a table partition, or a table subpartition. Please re-enable javascript in your browser settings. Oracle ALTER TABLE ADD column examples. SQL> alter table Books_master modify title VARCHAR2(20); Table altered. What is the default on the null clause? For object tables or relational tables with object columns, use ALTER TABLE to convert the table to the latest definition of its referenced type after the type has been altered. For example, the following statement makes the full_name column invisible: The following statement returns data from all columns of the accounts table except the full_name column: This is because the full_name column is invisible. For example: ALTER TABLE customers MODIFY customer_name varchar2(100) NOT NULL; when user does not enter anything in that column then that column will have the default value. Alter table to add primary key: 6.3.15. In Oracle 12c, it is now possible to specify the CURRVAL and NEXTVAL sequence pseudocolumns as the default values for a column. Obviously this c Let’s create a new table with some sample data for the demonstration. Inserting a record into that EMP table looks like this --SQL> insert into emp 2 (empno, ename, job, mgr, hiredate, sal, comm, deptno) 3 values The DEFAULT constraint is used to provide a default value for a column. While using this site, you agree to have read and accepted our Terms of Service and Privacy Policy. I cannot see anything in the alter table command but I'm sure you know better.I also noticed, in a quiet five minutes, that it is possible to create a NOT NULL column with a NULL default. To do this, we use the ALTER TABLE Modify Column command. The following CREATE TABLE statement creates the purchase_orderstable: How to add default value in the column of the Oracle database table? OracleTututorial.com website provides Developers and Database Administrators with the updated Oracle tutorials, scripts, and tips. To disable a previously set default, use DROP DEFAULT (alternatively, you can specify NULL as the default-value). ALTER TABLE syntax - missing DIRECTORY keyword. All Rights Reserved. Based on the departments table below, rename the departments table to depts. You can define invisible column when you create the table or using ALTER TABLE MODIFY column statement. Oracle provides "alter table" syntax to modify data columns in-place in this form: alter table table_name modify column_name datatype; If you are brave you can use a single "alter table" syntax to modify multiple columns: alter table table_name modify Invisible columns are not available for the query like: However, you can query the invisible columns by specify them explicitly in the query: By default, table columns are visible. For Oracle and MySQL, the SQL syntax for ALTER TABLE Modify Column is, sql - example - oracle alter table modify column null with default value . In this example here we will create a table which will use a sequence as a default value. Question: Is there an overhead when a add a column default value to a table? MODIFY [COLUMN]. This Oracle ALTER TABLE example will add a column called customer_name to the customers table that is a data type of varchar2(45). Adding a column with a default value to a table Tom, I have a doubt about adding columns with default values to a table. The only difference between the two is that in using the Sequence as a default value, you cannot have an implicit “Not Null” and “Not Deferrable” constraints. This feature is pretty much similar to the Identity Columns feature, which has also been introduced in 12c. Answer: Oracle allows you to change a table with a NOT NULL constraint to a NULL constraint with an "alter table" statement. To check whether a column exists in a table, you query the data from the user_tab_cols view. [Orders] ADD CONSTRAINT [DF_Orders_Timestamp] DEFAULT getdate() for OrderCreated. I understand that when you add a DEFAULT value to a column which is Nullable, Oracle updates all the NULL values for the column to the DEFAULT value, generating a lot of undo/redo data. Purpose. To add a new column to a table, you use the following syntax: ALTER TABLE table_name ADD column_name type constraint; For example, the following statement adds a new column named birthdate to the persons table: ALTER TABLE persons ADD birthdate DATE NOT NULL; If you view the persons table, you will see that the birthdate column is … Starting in Oracle 9i Release 2, you can now rename a column. To ADD A COLUMN in a table, the Oracle ALTER TABLE syntax is: Let's look at an example that shows how to add a column in an Oracle table using the ALTER TABLE statement. For example , suppose you create an NDB Cluster Disk Data table with two columns, using this CREATE TABLE statement: mysql> CREATE TABLE t3 (c1 INT, c2 INT)-> TABLESPACE ts_1 STORAGE DISK ENGINE NDB; Query OK, 0 rows affected (1.34 sec) To change column … I cannot see anything in the alter table command but I'm sure you know better.I also noticed, in a quiet five minutes, that it is possible to create a NOT NULL column with a NULL default. sql - example - oracle alter table modify column null with default value . alter table cust_table add cust_sex varchar2(1) NOT NULL; Here is an example of Oracle "alter table" syntax to add multiple data columns. If altering the data type of the column is a suitable solution, the code below will successfully alter the table to store SYS_GUID() values as identifiers: ALTER TABLE TEST_1.PERSON MODIFY( ID VARCHAR2(32) DEFAULT SYS_GUID() ); If you must have a numeric value as the ID in your table, there is an excellent answer here: Summary: in this tutorial, you will learn how to use the Oracle ALTER TABLE MODIFY column statement to change the definition of existing columns. To change the default value of the status column to 0, you use the following statement: We can add a new row to the accounts table to check whether the default value of the status column is 0 or 1: As you can see, the value in the status column for the account with id 4 is 0 as expected. What will the row show now? What is the default on the null clause? What will the row show now? To do this, we use the ALTER TABLE Modify Column command. If a field is added, its default value or NULL will be used as the value of this field in existing rows that do not contain it. A column default is rarely changed at alter table time, but there are issues with NULL values and default values. Alter table to modify default value of column (3) I have a requirement where we need to modify a column's default value in database table. Uses. CREATE TABLE t1 (c1 INT); ALTER TABLE t1 ADD COLUMN c2 INT GENERATED ALWAYS AS (c1 + 1) STORED; The data type and expression of generated columns can be modified. To RENAME A COLUMN in an existing table, the Oracle ALTER TABLE syntax is: Let's look at an example that shows how to rename a column in an Oracle table using the ALTER TABLE statement. alter table tab modify (percentage varchar2(100 byte)); ORA-54033: column to be modified is used in a virtual column expression; select column_name, data_default, hidden_column First, example the constraints with the desc SQL*Plus command: SQL> desc invoice The data types of the created_at and updated_at columns are TIMESTAMP WITH TIME ZONE.These columns also do not accept null. Now, you can use the NextVal and CurrVal sequence pseudo-columns as a default value for the table columns. You can also specify the DEFAULT value for columns i.e. For some types of tables (for example, tables without LOB columns), if you specify both a NOT NULL constraint and a default value, the database can optimize the column add operation and greatly reduce the amount of time that the table is locked for DML.