Create and use views

A view can be used to access data in one or more tables or views. You create a view by using a SELECT statement.

For example, to create a view that selects only the family name and the department of all the managers, specify:

     CREATE VIEW CORPDATA.EMP_MANAGERS AS
        SELECT LASTNAME, WORKDEPT FROM  CORPDATA.EMPLOYEE
        WHERE JOB = 'MANAGER'

Once you have created the view, you can use it in SQL statements just like a table name. You can also change the data in the base table. The following SELECT statement displays the contents of EMP_MANAGERS:

     SELECT *
           FROM CORPDATA.EMP_MANAGERS

The results are:

LASTNAME	WORKDEPT
THOMPSON	B01
KWAN	C01
GEYER	E01
STERN	D11
PULASKI	D21
HENDERSON	E11
SPENSER	E21

If the select list contains elements other than columns such as expressions, functions, constants, or special registers, and the AS clause was not used to name the columns, a column list must be specified for the view. In the following example, the columns of the view are LASTNAME and YEARSOFSERVICE.

     CREATE VIEW CORPDATA.EMP_YEARSOFSERVICE
         (LASTNAME, YEARSOFSERVICE) AS
        SELECT LASTNAME, YEAR (CURRENT DATE - HIREDATE)
        FROM CORPDATA.EMPLOYEE

Since the results of querying this view change as the current year changes, they are not included here.

The previous view can also be defined by using the AS clause in the select list to name the columns in the view. For example:

    CREATE VIEW CORPDATA.EMP_YEARSOFSERVICE AS
        SELECT LASTNAME,
                YEARS (CURRENT_DATE - HIREDATE) AS YEARSOFSERVICE
        FROM CORPDATA.EMPLOYEE

Using the UNION keyword, you can combine two or more subselects to form a single view. For example:

CREATE VIEW D11_EMPS_PROJECTS AS
  (SELECT EMPNO
     FROM CORPDATA.EMPLOYEE
     WHERE WORKDEPT = 'D11'
   UNION
   SELECT EMPNO
     FROM CORPDATA.EMPPROJACT
     WHERE PROJNO = 'MA2112' OR
        PROJNO = 'MA2113' OR
        PROJNO = 'AD3111')

Results in a view with the following data:

Table 1. Create a view as UNION results
EMPNO
000060
000150
000160
000170
000180
000190
000200
000210
000220
000230
000240
200170
200220

Views are created with the sort sequence in effect at the time the CREATE VIEW statement is run. The sort sequence applies to all character, or UCS-2 or UTF-16 graphic comparisons in the CREATE VIEW statement subselect.

Views can also be created using the WITH CHECK OPTION to specify the level of checking that should be done when data is inserted or updated through the view.