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Managing Tables

Managing Tables. Objectives. After completing this lesson, you should be able to do the following: Identify the various methods of storing data Outline Oracle data types Distinguish between an extended versus a restricted ROWID Outline the structure of a row

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Managing Tables

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  1. Managing Tables

  2. Objectives • After completing this lesson, you should be able to do the following: • Identify the various methods of storing data • Outline Oracle data types • Distinguish between an extended versus a restricted ROWID • Outline the structure of a row • Create regular and temporary tables • Manage storage structures within a table • Reorganize, truncate, drop a table • Drop a column within a table

  3. Storing User Data Regular table Partitionedtable Index-organizedtable Cluster

  4. Oracle Built-in Data Types Data type User-defined Built-in Scalar Collection Relationship CHAR(N), NCHAR(N)VARCHAR2(N),NVARCHAR2(N) NUMBER(P,S) DATETIMESTAMP RAW(N)BLOB, CLOB, NCLOB, BFILE LONG, LONG RAW ROWID, UROWID VARRAYTABLE REF

  5. . . BBBBBBBB RRRR FFFF Block number Row number File number ROWID Format • Extended ROWID Format • Restricted ROWID Format OOOOOO FFF BBBBBB RRR Data object number Relative file number Block number Row number

  6. Structure of a Row Row header Column length Database block Column value

  7. Creating a Table CREATE TABLE hr.employees( employee_id NUMBER(6), first_name VARCHAR2(20), last_name VARCHAR2(25), email VARCHAR2(25), phone_number VARCHAR2(20), hire_date DATE DEFAULT SYSDATE, job_id VARCHAR2(10), salary NUMBER(8,2), commission_pct NUMBER (2,2), manager_id NUMBER(6), department_id NUMBER(4) );

  8. Creating a Table: Guidelines • Place tables in separate tablespaces. • Use locally-managed tablespaces to avoid fragmentation. • Use few standard extent sizes for tables to reduce tablespace fragmentation.

  9. Creating Temporary Tables • Created using the GLOBAL TEMPORARY clause • Tables retain data only for the duration of a transaction or session • DML locks are not acquired on the data • Can create indexes, views, and triggers on temporary tables CREATE GLOBAL TEMPORARY TABLE hr.employees_temp AS SELECT * FROM hr.employees;

  10. Average Row Size * 100100 -PCTFREE- Available Data Space Setting PCTFREE and PCTUSED • Compute PCTFREE • Compute PCTUSED (Average Row Size - Initial Row Size) * 100 Average Row Size

  11. Row Migration and Chaining Before update After update Pointer

  12. ALTER TABLE hr.employees PCTFREE 30 PCTUSED 50 STORAGE(NEXT 500K MINEXTENTS 2 MAXEXTENTS 100); Changing Storage and Block Utilization Parameters

  13. ALTER TABLE hr.employees ALLOCATE EXTENT(SIZE 500K DATAFILE ‘/DISK3/DATA01.DBF’); Manually Allocating Extents

  14. Nonpartitioned Table Reorganization • When a nonpartitioned table is reorganized, its structure is kept, but not its contents. • Used to move a table to a different tablespace or reorganize extents. ALTER TABLE hr.employees MOVE TABLESPACE data1;

  15. Truncating a Table • Truncating a table deletes all rows in a table and releases used space. • Corresponding indexes are truncated. TRUNCATE TABLE hr.employees;

  16. Dropping a Table DROP TABLE hr.department CASCADE CONSTRAINTS;

  17. Dropping a Column • Removing a column from a table: • Removes the column length and data from each row, freeing space in the data block. • Dropping a column in a large table takes a considerable amount of time. ALTER TABLE hr.employees DROP COLUMN comments CASCADE CONSTRAINTS CHECKPOINT 1000;

  18. Using the UNUSED Option • Mark a column as unused: • Drop unused columns: • Continue to drop column operation: ALTER TABLE hr.employees SET UNUSED COLUMN comments CASCADE CONSTRAINTS; ALTER TABLE hr.employees DROP UNUSED COLUMNS CHECKPOINT 1000; ALTER TABLE hr.employees DROP COLUMNS CONTINUE CHECKPOINT 1000;

  19. Obtaining Table Information • Information about tables can be obtained by querying • the following views: • DBA_TABLES • DBA_OBJECTS

  20. Summary • In this lesson, you should have learned how to: • Distinguish between an extended versus a restricted ROWID • Outline the structure of a row • Create regular and temporary tables • Manage storage structures within a table • Reorganize, truncate, and drop a table • Drop a column within a table

  21. Practice 11 Overview • This practice covers the following topics: • Creating a table • Viewing, marking as unused, and dropping columns within a table • Allocating extents manually • Truncating a table • Obtaining table information

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