Working With DB2 Tables, Views, And Indexes

8/6/2019 Working With DB2 Tables, Views, And Indexes

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IBM DB2 9

2008 IBM Corporation

Section -5) Working with DB2 Tables,Working with DB2 Tables,Views, and IndexesViews, and Indexes

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Section 5Section 5 -- Working with DB2 Tables,Working with DB2 Tables,

Views, and Indexes (23.5%)Views, and Indexes (23.5%) Ability to demonstrate proper usage of DB2 data typesAbility to demonstrate proper usage of DB2 data types

Given a situation, ability to create a tableGiven a situation, ability to create a table

Ability to identify when referential integrity should be usedAbility to identify when referential integrity should be used

Ability to identify methods of data constraintAbility to identify methods of data constraint

Ability to identify characteristics of a table, view or indexAbility to identify characteristics of a table, view or index

Ability to identify when triggers should be usedAbility to identify when triggers should be used

Knowledge of schemasKnowledge of schemas

Knowledge of data type options for storing XML dataKnowledge of data type options for storing XML data

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Categories of Data Types in DB2 9

The built-in data types are categorized as follows:

Numeric

String

Date-time

XML

The user-defined data types are categorized as:

User-defined distinct type

User-defined structured type

User-defined reference type

In addition to these, special data types designed to beused with the DB2 Extenders.

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Built-in data types - Numeric

SMALLINT 2 Bytes

(-32,768 to 32,767)

INTEGER/INT 4 Bytes

(-2,147,483,648 to 2,147,483,647)

BIGINT 8 Bytes DECIMAL/DEC/NUM/NUMERIC

(p/2)+1 Ex. 67.12345 has precision

of 7, 7 2 is 3, + 1 makes 4

REAL/FLOAT 4 Bytes

(1.175E-37 to 3.402E+38)

DOUBLE 8 Bytes

(2.225E-307 to 1.79769E+308)


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DB2 Extenders

Provide support for complex, nontraditional data

types

Packaged separately from the DB2 server code and

is database dependant

For example, the DB2 Image Extender includes:

- The DB2IMAGE UDT

-UDFs to insert/retrieve from a db2image column

- APIs to search based on characteristics of images

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Tables

All data is stored in tables in the database. A tableconsists of one or more columns of various datatypes. The data is stored in rows or records.

May be defined using:

- The CREATE TABLE SQL statement

- A GUI tool, the DB2 Control Center

The catalog view SYSCAT.TABLES contains a row

for each table defined in the database.SYSCAT.COLUMNS contains a row for each columnof each table in the database.

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CREATE TABLE SQL

CREATE TABLE [TableName]([Column], ...)

[ColumnName][DataType]


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Creating Tables with Identity Columns

DB2 Database Manager can automatically generate numbersfor a column if the column is defined as an identity column.The syntax used to create an identity column is:

[ColumnName][DataType] GENERATED AS IDENTITY

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Constraints

Unique constraints, which are used to ensure that values ina column are unique [UNIQUE | PRIMARY KEY]

Referential integrity constraints, which are used to definerelationships between tables.

REFERENCES

[PKTableName]


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Examples

CREATE TABLE payroll.employees (empid INTEGERPRIMARY KEY,

emp_name CHAR(30), mgrno INTEGER,

CONSTRAINT fkconst FOREIGN KEY (mgrno)

REFERENCES payroll.employees(empid) )

CREATE TABLE payroll.paychecks (

empid INTEGER, weeknumber CHAR(3),

pay_amt DECIMAL(6,2),

CONSTRAINT fkconst FOREIGN KEY (empid)REFERENCES employee(empid) ON DELETE

CASCADE,

CONSTRAINT chk1 CHECK (pay_amt > 0 AND

weeknumber BETWEEN 1 AND 52))

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Examples

CREATE TABLE stock.activity (activityno SMALLINTNOT NULL

GENERATED BY DEFAULT AS IDENTITY

(START WITH 10 INCREMENT BY 10),

actkwd CHAR(6)WITH DEFAULT Action)

CREATE TABLE stock.copy LIKE stock.activity

CREATE TABLE part_table (

col1 INT, col2 CHAR(3))

PARTITION BY (col1 NULLS FIRST)(STARTING 0 ENDING 9 IN tbsp0,

STARTING 10 ENDING 19 IN tbsp1,

STARTING 20 ENDING 29 IN tbsp2,

STARTING 30 ENDING 39 IN tbsp3)

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Alter Table

Using it you can add ordrop:

A column

A primary key

One or more uniqueor referentialconstraints

One or more checkconstraints

You can also change:

The identity attributes of a column

The length of a string column(Only increase)

The datatype of a column but newdatatype must be compatible. Forexample, convert an INTEGERcolumn to BIGINT is possible, but,

a DECIMAL(10,2) column cannotbe converted to SMALLINT

The nullability of a column

The constraint of a column

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Informational Constraints

Informational Constraints are notenforced during insert andupdate processing. However,the DB2 SQL Optimizer willevaluate an informationalconstraint when resolve a query.

Defined by appending thekeywordsNOT ENFORCEDENABLE QUERY

OPTIMIZATION to a normalconstraint

NOT ENFORCED constraints are never checked by the

system, Not even by SET INTEGRITY


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Temporarily Suspending Constraint Checking

Constraint checking for a table can be suspended temporarily

by executing the SET INTEGRITY statement.

- SET INTEGRITY FOR employees OFF

To resume constraint checking for the EMPLOYEES table that

constraint checking was suspended

- SET INTEGRITY FOR employees IMMEDIATE CHECKED

If you want to transfer all offending rows in a separate table

say BAD_ROWS

- SET INTEGRITY FOR employees IMMEDIATE CHECKED

FOR EXCEPTION IN employees USE bad_rows

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SET CURRENT SCHEMA

Schemas are objects that are used to logically classify andgroup other objects in the database.

Two-part naming convention to avoid namespace collisionsfor example, in PAYROLL.STAFF first part is schema name.

The CURRENT SCHEMA (or CURRENT_SCHEMA) specialregister contains a value that identifies the schema name if noschema/qualifier name is specified, default is authorization IDof the current session user.

To change the value of the CURRENT SCHEMA,

SET CURRENT SCHEMA= 'PAYROLL'

On reconnect, the CURRENT SCHEMA special register willcontain your authentication ID, not the value you assigned itearlier.

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Declared Temporary Tables

It is used to create temporary tables that are used only duringa session.

The only object that can be DECLARED is a table.

These tables are not persistent and can be used only by the

application that creates them. When the applicationterminates, the rows of the table are deleted, and thedefinition of the table is dropped.

DECLARE GLOBAL TEMPORARY TABLE

T1 LIKE TRANSACTIONS

ON COMMIT PRESERVE ROWS

NOT LOGGED IN SESSION TEMP;

(LOB data will be replaced by zeros)

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A Closer Look At Views

A view provides a transparent view of the data inunderlying tables. Contains no data itself. Appears

just like a table to the user. Can also be used torestrict which rows and columns can be viewed or

updatedYou can create a view on an existing table (or tables)or on another view or any combination. A view definedon another view is called a nested view.

If a table or another view on which a view is based isdropped, the view remains defined in the database butbecomes inoperative.


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Views with CHECK Options

Data may be inserted or updated in the underlying tablesthrough a view.

CREATE VIEW nonfictionbooks AS

SELECT * FROM books WHERE booktype = 'N

WITH CHECK OPTION

WITH CHECK OPTION tells DB2 to check that statementsusing the view satisfy the conditions of the view.

WITH CASCADED CHECK OPTION must satisfy the

conditions of the view and all underlying views, even if thoseviews were not defined with the check option.

WITH LOCAL CHECK OPTION need only satisfy conditionsof views which have the check option specified.

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CREATE VIEW NONFICTIONBOOKS AS

SELECT * FROM BOOKSWHERE BOOKTYPE = 'N'

CREATE VIEW NFBOOKS2 AS

SELECT * FROM NONFICTIONBOOKS

WHERE BOOKID > 100

WITH CASCADED CHECK OPTION

INSERT INTO NFBOOKS2 VALUES(10,..,'N')INSERT INTO NFBOOKS2 VALUES(10,..,'F')

INSERT INTO NFBOOKS2 VALUES(120,..,'F')

INSERT INTO NFBOOKS2 VALUES(120,..,N')

WITH LOCAL CHECK OPTION

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A Closer Look At Indexes

An index is an object that contains an ordered set of pointersthat refer to rows in a base table.

Two reasons why you might create an index:

- To ensure uniqueness of values in a column or columns.

-To improve performance of queries against the table whendefined on the appropriate column(s).

Non-unique indexes allow duplicate key values; uniqueindexes allow only one occurrence of a key value in the listincluding a single null value.

Indexes are additional copies of the values so they must beupdated if the data in the table is updated. For frequentupdates, this could impact performance.

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Example of creating a non-unique index in ascending order :

- CREATE INDEX ibookname ON books (bookname)

You can specify different orders for the columns in the index:

- CREATE INDEX i2bookname ON books (authoid

DESC, bookname ASC)

Specify a bidirectional index:

-CREATE INDEX bibookname ON books (bookname)ALLOW REVERSE SCANS

A clustering index increases performance by decreasing no.of I/O, since like data values are stored on the same page.

- CREATE UNIQUE INDEX indx ON employees

(empno) CLUSTER

An index can be placed in a separate table space from thetable, but only in the CREATE TABLE statement.


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Another Look at Triggers

A trigger is used to define a set of actions that are to beexecuted whenever an insert, update, or delete operation isperformed against a table or updatable view.

Like constraints, triggers are often used to enforce dataintegrity and business rules.

Unlike constraints, triggers can also be used to update othertables, automatically generate or transform values for insertedor updated rows, and invoke functions to perform tasks suchas issuing errors or alerts.

Ex. CREATE TRIGGER pay_raiseBEFORE UPDATE ON employees

FOR EACH ROW

SET new.salary = salary * 1.1

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1) Which of the following DB2 data types

does NOT have a fixed length?

-

A. INT-B. CHAR

-C. XML

-D. DOUBLE

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2) Which of the following is the best statement to use

to create a user-defined data type that can be used

to store currency values?

A. CREATE DISTINCT TYPE currency AS

NUMERIC(7,2)

B. CREATE DISTINCT TYPE currency AS

SMALLINT

C. CREATE DISTINCT TYPE currency AS

BIGINT

D. CREATE DISTINCT TYPE currency AS

DOUBLE


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can be used to store 1000 MB of single-byte character data?

A. BLOB

B. CLOB

C. DBCLOB

D. GRAPHIC

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can NOT be used to create an identitycolumn?

A. SMALLINT

B. INTEGER

C. NUMERICD. DOUBLE

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5) Which of the following strings can NOT

be inserted into an XML column using

XMLPARSE()?

A. ""

B. "John Doe"

C. ""

D. "
"
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6) Which two of the following are optional

and do not have to be specified when

creating a table?

A. Table name

B. Column name

C. Default constraint

D. Column data type

E. NOT NULL constraint


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7) Given the following CREATE TABLE statement:

CREATE TABLE table2 LIKE table1

Which two of the following will NOT occur when the

statement is executed?

A. TABLE2 will have the same column names and column data

types as TABLE1

B. TABLE2 will have the same column defaults as TABLE1

C. TABLE2 will have the same nullability characteristics as

TABLE1

D. TABLE2 will have the same indexes as TABLE1.

E. TABLE2 will have the same referential constraints as TABLE1

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8) If table TAB1 is created using the following

statement:CREATE TABLE tab1 (col1 INTEGER NOT NULL,

col2 CHAR(5), CONSTRAINT cst1 CHECK

(col1 in (1, 2, 3)))

Which of the following statements will successfully

insert a record into table TAB1?

A. INSERT INTO tab1 VALUES (0, 'abc')

B. INSERT INTO tab1 VALUES (NULL, 'abc')

C. INSERT INTO tab1 VALUES (ABS(2), 'abc')

D. INSERT INTO tab1 VALUES (DEFAULT, 'abc')

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9) Which of the following is NOT a characteristic of a

unique index?

A. Each column in a base table can only participate in one

unique index, regardless of how the columns are grouped (the

same column cannot be used in multiple unique indexes)

B. In order for an index to be used to support a unique

constraint, it must have been defined with the UNIQUE attribute

C. A unique index cannot be created for a populated table if the

key column specified contains more than one NULL value

D. A unique index can only be created for a non-nullable

column

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10) Which of the following is NOT true about schemas?

A. If a schema name is not specified, either by qualifying a

database object name or by executing the SET CURRENT

SCHEMA statement, the authorization ID of the current

session user is used as the schema name by defaultB. The value assigned to the CURRENT SCHEMA special

register is persistent across database restarts

C. A schema enables the creation of multiple objects in a

database without encountering namespace collisions

D. When most database objects are created, they are

either implicitly or explicitly assigned to a schema


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11) Given the following statements:

CREATE TABLE table1(col1 INTEGER, col2 CHAR(3));

CREATE VIEW view1 AS SELECT col1, col2

FROM table1 WHERE col1 < 100

WITH LOCAL CHECK OPTION;

Which INSERT statement will execute successfully?

A. INSERT INTO view1 VALUES (50, abc)

B. INSERT INTO view1 VALUES(100, abc)

C. INSERT INTO view1 VALUES(50, 'abc')

D. INSERT INTO view1 VALUES(100, 'abc')

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12) Which of the following actions will NOT

cause a trigger to be fired?

A. INSERT

B. DELETE

C. ALTER

D. UPDATE

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13) Which of the following CREATE TABLE

statements will NOT be successful?

A. CREATE TABLE t1 (c1 XML NOT NULL

UNIQUE, c2 INT)

B. CREATE TABLE t1 (c1 XML NOT NULL, c2

CHAR(20))

C. CREATE TABLE t1 (c1 XML CHECK (c1 IS

VALIDATED), c2 INT)

D. CREATE TABLE t1 (c1 XML, c2 XML)

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14) Which of the following is NOT a characteristic of a

declared temporary table?

A. Declared temporary tables are not persistent and

can only be used by the application that creates them

B. It is possible for many applications to create

declared temporary tables that have the same name

C. Declared temporary tables are created by

executing a CREATE TABLE statement with the

DECLARED GLOBAL TEMPORARY clause specified

D. Once the application that created a global

temporary table is terminated, any records in the table

are deleted and the table is automatically destroyed


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Working With DB2 Tables, Views, And Indexes

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