Tesco SQL Introductory questions and understanding concepts

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Which is the subset of SQL commands used to manipulate Oracle Database structures, including tables?

Data Definition Language (DDL)

What operator performs pattern matching?

LIKE operator

What operator tests column for the absence of data?

IS NULL operator

Which command executes the contents of a specified file?

START or @

What is the parameter substitution symbol used with INSERT INTO command?

&

Which command displays the SQL command in the SQL buffer, and then executes it?

RUN

What are the wildcards used for pattern matching?

_ for single character substitution and % for multi-character substitution

State true or false. EXISTS, SOME, ANY are operators in SQL.

True

State true or false. =, <> ^ = all denote the same operation.

True

What are the privileges that can be granted on a table by a user to others?

Insert, update, delete, select, references, index, execute, alter, all

What command is used to get back the privileges offered by the GRANT command?

REVOKE

Which system tables contain information on privileges granted and privileges obtained?

USER_TAB_PRIVS_MADE, USER_TAB_PRIVS_RECD

Which system table contains information on constraints on all the tables created?

  • USER_CONSTRAINTS
  • TRUNCATE TABLE EMP
  • DELETE FROM EMP

Will the outputs of the above two commands differ?

Both will result in deleting all the rows in the table EMP.

What is the difference between TRUNCATE and DELETE commands?

TRUNCATE is a DDL command whereas DELETE is a DML command. Hence DELETE operation can be rolled back, but TRUNCATE operation cannot be rolled back. WHERE clause can be used with DELETE and not with TRUNCATE.

What command is used to create a table by copying the structure of another table?

Answer: CREATE TABLE. AS SELECT command

Explanation: To copy only the structure, the WHERE clause of the SELECT command should contain a FALSE statement as in the following:

CREATE TABLE NEWTABLE AS SELECT * FROM EXISTINGTABLE WHERE 1 = 2.

If the WHERE condition is true, then all the rows or rows satisfying the condition will be copied to the new table.

What will be the output of the following query?

SELECT REPLACE (TRANSLATE (LTRIM (RTRIM ( ‘ATHEN!’ ‘’ ), ‘’ ), ‘AN’ ‘* *’ ), ‘*’ ‘TROUBLE’ ) FROM DUAL.

TROUBLETHETROUBLE

What will be the output of the following query?

SELECT DECODE (TRANSLATE ( ‘A’ '0 ‘'1’ ), ‘1’ ‘YES’ ‘NO’ ).

Answer: NO

Explanation: The query checks whether a given string is a numerical digit.

What does the following query do?

SELECT SAL + NVL (COMM, 0) FROM EMP.

This displays the total salary of all employees. The null values in the commission column will be replaced by 0 and added to salary.

Which date function is used to find the difference between two dates?

MONTHS_BETWEEN

Why does the following command give a compilation error?

DROP TABLE &TABLE_NAME.

Variable names should start with an alphabet. Here the table name starts with an ‘&’ symbol.

What is the advantage of specifying WITH GRANT OPTION in the GRANT command?

The privilege receiver can further grant the privileges he/she has obtained from the owner to any other user.

What is the use of the DROP option in the ALTER TABLE command?

It is used to drop constraints specified on the table.

What is the value of comM'and saL'after executing the following query if the initial value of saL'is 10000?

UPDATE EMP SET SAL = SAL + 1000, COMM = SAL * 0.1.

sal = 11000, comm = 1000

What is the use of DESC in SQL?

Answer: DESC has two purposes. It is used to describe a schema as well as to retrieve rows from table in descending order.

Explanation: The query SELECT * FROM EMP ORDER BY ENAME DESC will display the output sorted on ENAME in descending order.

What is the use of CASCADE CONSTRAINTS?

When this clause is used with the DROP command, a parent table can be dropped even when a child table exists.

Which function is used to find the largest integer less than or equal to a specific value?

FLOOR

What is the output of the following query?

SELECT TRUNC (1234.5678, 2) FROM DUAL; 1200