Q. What is Oracle table?
A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.
- Hide data complexity.
- Simplify commands for the user.
- Present the data in a different perspective from that of the base table.
- Store complex queries.
- Provide public access to an object
- Provide location transparency for tables, views or program units of a remote database.
- Simplify the SQL statements for database users.
Q. What is hash cluster?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stored together on the disk.
Q. What is data block?
Oracle database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.
Database triggers do not fire on TRUNCATE
Self Join - Joining the table with itself.
Equi Join - Joining two tables by equating two common columns.
Non-Equi Join - Joining two tables by equating two common columns.
Outer Join - Joining two tables in such a way that query can also retrieve rows that do not have corresponding join value in the other table.
INSTR returns the position of the m-th occurrence of the string 2 in string1. The search begins from nth position of string1.
SUBSTR (String1 n, m)
SUBSTR returns a character string of size m in string1, starting from n-th position of string1.
MINUS - returns all distinct rows selected by the first query but not by the second.
UNION - returns all distinct rows selected by either query
UNION ALL - returns all rows selected by either query, including all duplicates.
CHAR pads blank spaces to the maximum length.
VARCHAR2 does not pad blank spaces.
For CHAR the maximum length is 255 and 2000 for VARCHAR2.
- To add a column with NOT NULL constrain, the table must be empty.
- To hide complexity of a query.
- To hide complexity of calculations.
Q. Can a view be updated/inserted/deleted? If Yes - under what conditions?
A View can be updated/deleted/inserted if it has only one base table if the view is based on columns from one or more tables then insert, update and delete is not possible.
An ALTER CONSTRAINT command does not exist. Constraints are changed by the ALTER TABLE command. A CREATE CONSTRAINT command does not exist. Constraints are created through the CREATE TABLE or ALTER TABLE command. This question is a little tricky, because, although constraints can have their behavior changed and they are obviously created, the commands that do so are taking action on a table and not on the constraint directly. Constraints cannot be deleted-they must be dropped.
Q. A DDL operation can be rolled-back (True/False)?
False
Q. Which DATATYPE in Oracle is used to store Image files, Audio/Video files, etc.?
RAW, BLOB, BFILE, CLOB
Q. Describe the difference between a procedure, function and anonymous pl/sql block.
use of DECLARE statement, a function must return a value while a procedure doesn’t have to.
Q. What is a mutating table error and how can you get around it?
This happens with triggers. It occurs because the trigger is trying to update a row it is currently using. The usual fix involves either use of views or temporary tables so the database is selecting from one while updating the other.
Q. Describe the use of %ROWTYPE and %TYPE in PL/SQL
%ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type.
Q. What packages (if any) has Oracle provided for use by developers?
Oracle provides the DBMS_ series of packages. There are many which developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and describe how they used them, even better. If they include the SQL routines provided by Oracle, great, but not really what was asked.
Q. Describe the use of PL/SQL tables
PL/SQL tables are scalar arrays that can be referenced by a binary integer. They can be used to hold values for use in later queries or calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.
Q. When is a declare statement needed ?
The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if it is used.
Q. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?
OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL.
Q. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.
Q. How can you find within a PL/SQL block, if a cursor is open?
Use the %ISOPEN cursor status variable.
Q. How can you generate debugging output from PL/SQL?
Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE can also be used.
Q. What are the types of triggers?
There are 12 types of triggers in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL key words:
BEFORE ALL ROW INSERT
AFTER ALL ROW INSERT
BEFORE INSERT
AFTER INSERT etc.
Q. How can you tell if a database object is invalid?
By checking the status column of the DBA_, ALL_ or USER_OBJECTS views, depending upon whether you own or only have permission on the view or are using a DBA account.
Q. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check?
You need to check that the user has specified the full name of the object (select empid from scott.emp; instead of select empid from emp;) or has a synonym that points to the object (create synonym emp for scott.emp;)
Q. A developer is trying to create a view and the database won’t let him. He has the "DEVELOPER" role which has the "CREATE VIEW" system privilege and SELECT grants on the tables he is using, what is the problem?
You need to verify the developer has direct grants on all tables used in the view. You can’t create a stored object with grants given through views.
Q. If you have an example table, what is the best way to get sizing data for the production table implementation?
The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows.
Q. How can you call a PL/SQL procedure from SQL?
By use of the EXECUTE (short form EXEC) command.
Q. How do you execute a host operating system command from within SQL?
By use of the exclamation point "!" (in UNIX and some other OS) or the HOST (HO) command.
Q. You want to use SQL to build SQL, what is this called and give an example
This is called dynamic SQL. An example would be:
set lines 90 pages 0 termout off feedback off verify off
spool drop_all.sql
select ‘drop user ‘||username||’ cascade;’ from dba_users
where username not in ("SYS’,’SYSTEM’);
spool off
Essentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ‘||’ the values selected from the database.
Q. What SQLPlus command is used to format output from a select?
This is best done with the COLUMN command.
Q. What is the default ordering of an ORDER BY clause in a SELECT statement?
Ascending
Q. How do you set the number of lines on a page of output? The width?
The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.
Q. How do you prevent output from coming to the screen?
The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.
Q. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution?
The SET options FEEDBACK and VERIFY can be set to OFF.
Q. How do you generate file output from SQL?
By use of the SPOOL command
Q. What is the fastest query method for a table?
Fetch by rowid
Q. Describe third normal form?
Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key
Q. Is the following statement true or false:
"All relational databases must be in third normal form"
Why or why not?
False. While 3NF is good for logical design most databases, if they have more than just a few tables, will not perform well using full 3NF. Usually some entities will be denormalized in the logical to physical transfer process.
Q. What is an ERD?
An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model.
Q. Why are recursive relationships bad? How do you resolve them?
A recursive relationship (one where a table relates to itself) is bad when it is a hard relationship (i.e. neither side is a "may" both are "must") as this can result in it not being possible to put in a top or perhaps a bottom of the table (for example in the EMPLOYEE table you couldn’t put in the PRESIDENT of the company because he has no boss, or the junior janitor because he has no subordinates). These type of relationships are usually resolved by adding a small intersection entity.
Q. What does a hard one-to-one relationship mean (one where the relationship on both ends is "must")?
This means the two entities should probably be made into one entity.
Q. How should a many-to-many relationship be handled?
By adding an intersection entity table
Q. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used?
A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key.
Q. When should you consider denormalization?
Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity.
Q. How can you determine the space left in a file system?
There are several commands to do this: du, df, or bdf
A table is the basic unit of data storage in an Oracle database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.
Q. What is an Oracle view?
A view is a virtual table. Every view has a query attached to it. (The query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)Q. Do a view contain data?
Views do not contain or store data.Q. Can a view based on another view?
Yes.Q. What are the advantages of views?
- Provide an additional level of table security, by restricting access to a predetermined set of rows and columns of a table.- Hide data complexity.
- Simplify commands for the user.
- Present the data in a different perspective from that of the base table.
- Store complex queries.
Q. What is an Oracle sequence?
A sequence generates a serial list of unique numbers for numerical columns of a database's tables.Q. What is a synonym?
A synonym is an alias for a table, view, sequence or program unit.Q. What are the types of synonyms?
There are two types of synonyms private and public.Q. What is a private synonym?
Only its owner can access a private synonym.Q. What is a public synonym?
Any database user can access a public synonym.Q. What are synonyms used for?
- Mask the real name and owner of an object.- Provide public access to an object
- Provide location transparency for tables, views or program units of a remote database.
- Simplify the SQL statements for database users.
Q. What is an Oracle index?
An index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.Q. How are the index updates?
Indexes are automatically maintained and used by Oracle. Changes to table data are automatically incorporated into all relevant indexes.Q. What are clusters?
Clusters are groups of one or more tables physically stores together to share common columns and are often used together.Q. What is cluster key?
The related columns of the tables in a cluster are called the cluster key.Q. What is index cluster?
A cluster with an index on the cluster key.Q. What is hash cluster?
A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stored together on the disk.
Q. When can hash cluster used?
Hash clusters are better choice when a table is often queried with equality queries. For such queries the specified cluster key value is hashed. The resulting hash key value points directly to the area on disk that stores the specified rows.Q. What is data block?
Oracle database's data is stored in data blocks. One data block corresponds to a specific number of bytes of physical database space on disk.
Q. How to define data block size?
A data block size is specified for each Oracle database when the database is created. A database users and allocated free database space in Oracle data blocks. Block size is specified in init.ora file and cannot be changed latter.Q. What is a deadlock? Explain.
Two processes waiting to update the rows of a table, which are locked by other processes then deadlock arises. In a database environment this will often happen because of not issuing the proper row lock commands. Poor design of front-end application may cause this situation and the performance of server will reduce drastically. These locks will be released automatically when a commit/rollback operation performed or any one of this processes being killed externally.Q. What are the types of SQL statement?
Data Definition Language (DDL): CREATE, ALTER, DROP, TRUNCATE, REVOKE, NO AUDIT & COMMIT.Data Manipulation Language (DML): INSERT, UPDATE, DELETE, LOCKTABLE, EXPLAIN PLAN & SELECT.
Transactional Control: COMMIT & ROLLBACK
Session Control: ALTERSESSION & SET ROLE
System Control: ALTER SYSTEM.
Q. What is a transaction?
Transaction is logical unit between two commits and commit & rollback.Q. What is difference between TRUNCATE & DELETE?
TRUNCATE commits after deleting entire table i.e., cannot be rolled back.Database triggers do not fire on TRUNCATE
DELETE allows the filtered deletion. Deleted records can be rolled back or committed. Database triggers fire on DELETE.
Q. What is a join? Explain the different types of joins?
Join is a query, which retrieves related columns or rows from multiple tables.Self Join - Joining the table with itself.
Equi Join - Joining two tables by equating two common columns.
Non-Equi Join - Joining two tables by equating two common columns.
Outer Join - Joining two tables in such a way that query can also retrieve rows that do not have corresponding join value in the other table.
Q. What is the sub-query?
Sub-query is a query whose return values are used in filtering conditions of the main query.Q. What is correlated sub-query?
Correlated sub-query is a sub-query, which has reference to the main query.Q. Explain CONNECT BY PRIOR?
Retrieves rows in hierarchical order Q. Difference between SUBSTR and INSTR?
INSTR (String1, String2 (n, (m)),INSTR returns the position of the m-th occurrence of the string 2 in string1. The search begins from nth position of string1.
SUBSTR (String1 n, m)
SUBSTR returns a character string of size m in string1, starting from n-th position of string1.
Q. Explain UNION, MINUS, UNION ALL and INTERSECT?
INTERSECT - returns all distinct rows selected by both queries.MINUS - returns all distinct rows selected by the first query but not by the second.
UNION - returns all distinct rows selected by either query
UNION ALL - returns all rows selected by either query, including all duplicates.
Q. What is ROWID?
ROWID is a pseudo column attached to each row of a table. It is 18 characters long, blockno, rownumber are the components of ROWID.Q. What is the fastest way of accessing a row in a table?
Using ROWID CONSTRAINTSQ. What is an integrity constraint?
Integrity constraint is a rule that restricts values to a column in a table.Q. What is referential integrity constraint?
Maintaining data integrity through a set of rules that restrict the values of one or more columns of the tables based on the values of primary key or unique key of the referenced table.Q. What is the usage of SAVEPOINTS?
SAVEPOINTS are used to subdivide a transaction into smaller parts. It enables rolling back part of a transaction. Maximum of five save points are allowed.Q. What is ON DELETE CASCADE?
When ON DELETE CASCADE is specified Oracle maintains referential integrity by automatically removing dependent foreign key values if a referenced primary or unique key value is removed.Q. What are the data types allowed in a table?
CHAR, VARCHAR2, NUMBER, DATE, RAW, LONG and LONG RAW.CHAR pads blank spaces to the maximum length.
VARCHAR2 does not pad blank spaces.
For CHAR the maximum length is 255 and 2000 for VARCHAR2.
Q. How many LONG columns are allowed in a table? Is it possible to use LONG columns in WHERE clause or ORDER BY?
Only one LONG column is allowed. It is not possible to use LONG column in WHERE or ORDER BY clause.Q. What are the pre-requisites to modify datatype of a column and to add a column with NOT NULL constraint?
- To modify the datatype of a column the column must be empty.- To add a column with NOT NULL constrain, the table must be empty.
Q. Where the integrity constraints are stored in data dictionary?
The integrity constraints are stored in USER_CONSTRAINTS.Q. How will you activate/deactivate integrity constraints?
The integrity constraints can be enabled or disabled by ALTER TABLE ENABLE CONSTRAINT / DISABLE CONSTRAINT.Q. If unique key constraint on DATE column is created, will it validate the rows that are inserted with SYSDATE?
It won't, Because SYSDATE format contains time attached with it.Q. How to access the current value and next value from a sequence? Is it possible to access the current value in a session before accessing next value?
Sequence name CURRVAL, sequence name NEXTVAL. It is not possible. Only if you access next value in the session, current value can be accessed.Q. What is CYCLE/NO CYCLE in a Sequence?
CYCLE specifies that the sequence continue to generate values after reaching either maximum or minimum value. After pan-ascending sequence reaches its maximum value, it generates its minimum value. After a descending sequence reaches its minimum, it generates its maximum.NO CYCLE specifies that the sequence cannot generate more values after reaching its maximum or minimum value.
Q. What are the advantages of VIEW?
- To protect some of the columns of a table from other users.- To hide complexity of a query.
- To hide complexity of calculations.
Q. Can a view be updated/inserted/deleted? If Yes - under what conditions?
A View can be updated/deleted/inserted if it has only one base table if the view is based on columns from one or more tables then insert, update and delete is not possible.
Q. What is the purpose of the IMPORT option IGNORE? What is it’s default setting?
The IMPORT IGNORE option tells import to ignore "already exists" errors. If it is not specified the tables that already exist will be skipped. If it is specified, the error is ignored and the tables data will be inserted. The default value is N.Q. What is the proper method for disabling and re-enabling a primary key constraint?
You use the ALTER TABLE command for both. However, for the enable clause you must specify the USING INDEX and TABLESPACE clause for primary keys.Q. What part of a database block is a new table record inserted into?
Free spaceIn a database block, row data is stored in the bytes allocated for free space, which then becomes part of the data space. The header contains general block information, such as the block address and the type of segment (for example, data, index, or rollback). The table directory holds information about the tables having rows in this block. The row directory contains information about the actual rows in the block.
Q. What happens if a primary key constraint is disabled and then enabled without fully specifying the index clause?
The index is created in the user’s default tablespace and all sizing information is lost. Oracle doesn’t store this information as a part of the constraint definition, but only as part of the index definition, when the constraint was disabled the index was dropped and the information is gone.Q. Which operations can be taken on a constraint?
DISABLE, DROP , ENABLEAn ALTER CONSTRAINT command does not exist. Constraints are changed by the ALTER TABLE command. A CREATE CONSTRAINT command does not exist. Constraints are created through the CREATE TABLE or ALTER TABLE command. This question is a little tricky, because, although constraints can have their behavior changed and they are obviously created, the commands that do so are taking action on a table and not on the constraint directly. Constraints cannot be deleted-they must be dropped.
Q. A DDL operation can be rolled-back (True/False)?
False
Q. Which DATATYPE in Oracle is used to store Image files, Audio/Video files, etc.?
RAW, BLOB, BFILE, CLOB
Q. Describe the difference between a procedure, function and anonymous pl/sql block.
use of DECLARE statement, a function must return a value while a procedure doesn’t have to.
Q. What is a mutating table error and how can you get around it?
This happens with triggers. It occurs because the trigger is trying to update a row it is currently using. The usual fix involves either use of views or temporary tables so the database is selecting from one while updating the other.
Q. Describe the use of %ROWTYPE and %TYPE in PL/SQL
%ROWTYPE allows you to associate a variable with an entire table row. The %TYPE associates a variable with a single column type.
Q. What packages (if any) has Oracle provided for use by developers?
Oracle provides the DBMS_ series of packages. There are many which developers should be aware of such as DBMS_SQL, DBMS_PIPE, DBMS_TRANSACTION, DBMS_LOCK, DBMS_ALERT, DBMS_OUTPUT, DBMS_JOB, DBMS_UTILITY, DBMS_DDL, UTL_FILE. If they can mention a few of these and describe how they used them, even better. If they include the SQL routines provided by Oracle, great, but not really what was asked.
Q. Describe the use of PL/SQL tables
PL/SQL tables are scalar arrays that can be referenced by a binary integer. They can be used to hold values for use in later queries or calculations. In Oracle 8 they will be able to be of the %ROWTYPE designation, or RECORD.
Q. When is a declare statement needed ?
The DECLARE statement is used in PL/SQL anonymous blocks such as with stand alone, non-stored PL/SQL procedures. It must come first in a PL/SQL stand alone file if it is used.
Q. In what order should a open/fetch/loop set of commands in a PL/SQL block be implemented if you use the %NOTFOUND cursor variable in the exit when statement? Why?
OPEN then FETCH then LOOP followed by the exit when. If not specified in this order will result in the final return being done twice because of the way the %NOTFOUND is handled by PL/SQL.
Q. What are SQLCODE and SQLERRM and why are they important for PL/SQL developers?
SQLCODE returns the value of the error number for the last error encountered. The SQLERRM returns the actual error message for the last error encountered. They can be used in exception handling to report, or, store in an error log table, the error that occurred in the code. These are especially useful for the WHEN OTHERS exception.
Q. How can you find within a PL/SQL block, if a cursor is open?
Use the %ISOPEN cursor status variable.
Q. How can you generate debugging output from PL/SQL?
Use the DBMS_OUTPUT package. Another possible method is to just use the SHOW ERROR command, but this only shows errors. The DBMS_OUTPUT package can be used to show intermediate results from loops and the status of variables as the procedure is executed. The new package UTL_FILE can also be used.
Q. What are the types of triggers?
There are 12 types of triggers in PL/SQL that consist of combinations of the BEFORE, AFTER, ROW, TABLE, INSERT, UPDATE, DELETE and ALL key words:
BEFORE ALL ROW INSERT
AFTER ALL ROW INSERT
BEFORE INSERT
AFTER INSERT etc.
Q. How can you tell if a database object is invalid?
By checking the status column of the DBA_, ALL_ or USER_OBJECTS views, depending upon whether you own or only have permission on the view or are using a DBA account.
Q. A user is getting an ORA-00942 error yet you know you have granted them permission on the table, what else should you check?
You need to check that the user has specified the full name of the object (select empid from scott.emp; instead of select empid from emp;) or has a synonym that points to the object (create synonym emp for scott.emp;)
Q. A developer is trying to create a view and the database won’t let him. He has the "DEVELOPER" role which has the "CREATE VIEW" system privilege and SELECT grants on the tables he is using, what is the problem?
You need to verify the developer has direct grants on all tables used in the view. You can’t create a stored object with grants given through views.
Q. If you have an example table, what is the best way to get sizing data for the production table implementation?
The best way is to analyze the table and then use the data provided in the DBA_TABLES view to get the average row length and other pertinent data for the calculation. The quick and dirty way is to look at the number of blocks the table is actually using and ratio the number of rows in the table to its number of blocks against the number of expected rows.
Q. How can you call a PL/SQL procedure from SQL?
By use of the EXECUTE (short form EXEC) command.
Q. How do you execute a host operating system command from within SQL?
By use of the exclamation point "!" (in UNIX and some other OS) or the HOST (HO) command.
Q. You want to use SQL to build SQL, what is this called and give an example
This is called dynamic SQL. An example would be:
set lines 90 pages 0 termout off feedback off verify off
spool drop_all.sql
select ‘drop user ‘||username||’ cascade;’ from dba_users
where username not in ("SYS’,’SYSTEM’);
spool off
Essentially you are looking to see that they know to include a command (in this case DROP USER...CASCADE;) and that you need to concatenate using the ‘||’ the values selected from the database.
Q. What SQLPlus command is used to format output from a select?
This is best done with the COLUMN command.
Q. What is the default ordering of an ORDER BY clause in a SELECT statement?
Ascending
Q. How do you set the number of lines on a page of output? The width?
The SET command in SQLPLUS is used to control the number of lines generated per page and the width of those lines, for example SET PAGESIZE 60 LINESIZE 80 will generate reports that are 60 lines long with a line width of 80 characters. The PAGESIZE and LINESIZE options can be shortened to PAGES and LINES.
Q. How do you prevent output from coming to the screen?
The SET option TERMOUT controls output to the screen. Setting TERMOUT OFF turns off screen output. This option can be shortened to TERM.
Q. How do you prevent Oracle from giving you informational messages during and after a SQL statement execution?
The SET options FEEDBACK and VERIFY can be set to OFF.
Q. How do you generate file output from SQL?
By use of the SPOOL command
Fetch by rowid
Q. Describe third normal form?
Something like: In third normal form all attributes in an entity are related to the primary key and only to the primary key
Q. Is the following statement true or false:
"All relational databases must be in third normal form"
Why or why not?
False. While 3NF is good for logical design most databases, if they have more than just a few tables, will not perform well using full 3NF. Usually some entities will be denormalized in the logical to physical transfer process.
Q. What is an ERD?
An ERD is an Entity-Relationship-Diagram. It is used to show the entities and relationships for a database logical model.
Q. Why are recursive relationships bad? How do you resolve them?
A recursive relationship (one where a table relates to itself) is bad when it is a hard relationship (i.e. neither side is a "may" both are "must") as this can result in it not being possible to put in a top or perhaps a bottom of the table (for example in the EMPLOYEE table you couldn’t put in the PRESIDENT of the company because he has no boss, or the junior janitor because he has no subordinates). These type of relationships are usually resolved by adding a small intersection entity.
Q. What does a hard one-to-one relationship mean (one where the relationship on both ends is "must")?
This means the two entities should probably be made into one entity.
Q. How should a many-to-many relationship be handled?
By adding an intersection entity table
Q. What is an artificial (derived) primary key? When should an artificial (or derived) primary key be used?
A derived key comes from a sequence. Usually it is used when a concatenated key becomes too cumbersome to use as a foreign key.
Q. When should you consider denormalization?
Whenever performance analysis indicates it would be beneficial to do so without compromising data integrity.
Q. How can you determine the space left in a file system?
There are several commands to do this: du, df, or bdf
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