DB2 gives us an option of modifying the attribute of the existing column in a table. We have to use the ALTER COLUMN parameter with ALTER TABLE as below in order to achieve this.ALTER TABLE DBSET1.TAB1    ALTER COLUMN NAME       SET DATATYPE CHAR(50);The ALTER TABLE reserved words are followed by the name of the table qualified by a database, which is DBSET1.TAB1 in this case. Similarly, ALTER COLUMN is followed by the name of the column which needs to be modified, which NAME (of the student) in this case.In the SET DATATYPE parameter, we can pass the ... Read More

DB2 gives us an option to copy the structure of an existing table to a new table. To copy the attributes and column of table TAB1 to a new table TAB2 we can use the following command−CREATE TABLE DBSET1.TAB2    LIKE DBSET1.TAB1The CREATE TABLE reserved words are followed by table name. The table name needs to be qualified by a database in which it will reside. In this case this new table is TAB2 and its database is DBSET1.The LIKE parameter is used after that followed by the name of the original table qualified by its database i.e. DBSET1.TAB1The important ... Read More

A view is an alternative way of representing the data stored in a table. A view can be used to increase the performance of the query since the view contains very limited rows as compared to its source table. We can use the below command to create a view on an existing table TAB1.CREATE VIEW AGEVIEW (NAME, AGE, ENROLLMENT_ID)    AS SELECT NAME, AGE, ENROLLMENT_ID FROM TAB1       WHERE AGE > 10;We have to use CREATE VIEW reserved words in order to create a new view. This will be followed by the name of the view (AGEVIEW).The columns ... Read More

A foreign key is a column in a table that establishes a referential link with another table. A foreign key can be defined during creation of table (CREATE TABLE command) or it can be defined by modifying the table (ALTER TABLE command). However, before defining any key as foreign key, make sure that an index is built up on that column. We can use the below command to define an existing column CLASS in table TAB1 as a foriegn key which links to table TAB2.ALTER TABLE TAB1 ADD FOREIGN KEY (CLASS) REFERENCES CLASSDATA (CLASS_ID);The ALTER TABLE reserved words are followed ... Read More

We can add a new column in an existing table as per the business requirements. Similarly, we can also remove a column from the table. This could be done using the ALTER table command as below.ALTER TABLE TAB1 ADD COLUMN ADDRESS VARCHAR(100);The ALTER TABLE reserved words are followed by the name of the table which we want to amend. In this case it is TAB1.To add a new column we will use ADD COLUMN and to remove the column we will use the REMOVE COLUMN parameter. This is followed by the name of the column. If this is an addition ... Read More

Constraints are used to restrict the data inserted at a particular column. Constraints can be used in such a way that a value can only be inserted if it satisfies the condition given in constraints. We can give the below parameter during CREATE TABLE command to add a constraint.CREATE TABLE DBSET1.TAB1    (STUDENT_ID CHAR(10) NOT NULL,    ENROLLMENT_ID CHAR(20) NOT NULL,    NAME VARCHAR(50),    AGE SMALLINT CONSTRAINT NUMBER CHECK    (AGE >=3 AND AGE

An index is a lookup table that optimizes the searching of data. An index defined on any table can increase the query speed. The index can be built up on any column of the table and DB2 will generate a logical structure at backend. This will facilitate the search on the table using indexed columns effectively.An index can be unique and non-unique. To create a new unique index at any table we can use below command.CREATE UNIQUE INDEX ENROTAB1    ON TAB1 (ENROLLMENT_ID) ASC;The CREATE UNIQUE INDEX reserved words are followed by the name of the unique index which we ... Read More

A table is a logical structure of a data in a DB2. A table consists of a column which represents the attribute and rows represents the entity. Below command can be issued in order to create a new DB2 table.CREATE TABLE DBSET1.TAB1    (STUDENT_ID CHAR(10) NOT NULL,    ENROLLMENT_ID CHAR(20) NOT NULL,    NAME VARCHAR(50),    AGE SMALLINT    PRIMARY KEY (STUDENT_ID));The CREATE TABLE reserved words are followed by the name of the table which we have to create in the format . Here DBSET1 is the database and TAB1 is the table.The name of the column has to be ... Read More

Bufferpool is the unit of the main memory which is used to cache the data in the DB2 table. The data is stored in the cache once the database manager reads the data from the disk to the main memory. The bufferpool can be defined by giving the pagesize.The page is the smallest unit of Input/Output that a DB2 database manager can handle. We can create a DB2 bufferpool using the below command−CREATE BUFFERPOOL BP3 PAGESIZE 4096;The CREATE and BUFFERPOOL reserved words are followed by the bufferpool name which we want to create. Finally we will use PAGESIZE parameter to ... Read More

A Volume is a group of physical disks which are used to store the data. A storage group is a collection of volumes. We can add or remove the volumes in a storage group in order to adjust the space. Below command can be issued in order to amend the volume in a storage group.ALTER STG1    ADD VOLUMES(VOL34)    REMOVE VOLUMES(VOL29);The ALTER reserved word has to be followed by the name of the storage group which needs to be altered. Which is STG1 in this case. The ADD VOLUMES parameter has the list of volumes which needs to be ... Read More