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What is primary key in DB2?
A primary key is a special type of unique key and cannot contain null values. For example, the DEPTNO column in the DEPT table is a primary key. A table can have no more than one primary key. When a primary key is defined in a CREATE TABLE statement or ALTER TABLE statement, DB2 automatically creates the primary index.
Can we update primary key in Db2?
Db2® interprets updating a primary key as a deletion, followed by an insertion of a new row the same as the deleted row but with the new primary key value. Change the primary key in the new row to the required value. Use the SAVE primary command to verify that there are no other Db2 errors.
How to find the primary key of a DB2 table TAB1?
The SYSIBM.SYSCOLUMNS is a DB2 system table which contains one row for every column of each table. It also contains the data related to the views. Below SQL query can be fired in order to find the primary key of a particular table. SELECT NAME FROM SYSIBM.SYSCOLUMNS WHERE TBNAME = ‘TAB1’ AND KEYSEQ > 0 ORDER BY KEYSEQ ASC;
Can a primary key be a NULL column in DB2?
However, in DB2, you must explicitly declare all primary key columns as NOT NULL columns. Because the primary key must contain unique values that uniquely identify each row of a table, the identity column is an ideal choice for the primary key. The following syntax shows how to create a table with a primary key as an identity column:
How to add primary key to SQL table?
To add a primary key to a table, you use the following form of ALTER TABLE statement: ALTER TABLE table_name [ ADD CONSTRAINT constraint_name] PRIMARY KEY (primary_key_columns); Code language: SQL (Structured Query Language) (sql) Note that the ADD CONSTRAINT clause is optional.
How to remove a primary key from a table?
Note that the ADD CONSTRAINT clause is optional. To remove a primary key from a table, you use the following form of the ALTER TABLE statement: The primary key of a table cannot contain NULL values.