What is SQL?
What is SELECT statement?
How can you compare a part of the name rather than the
entire name?
What is the INSERT statement?
How do you delete a record from a database?
How could I get distinct entries from a table?
How to get the results of a Query sorted in any order?
How can I find the total number of records in a table?
What is GROUP BY?
What is the difference among "dropping a table",
"truncating a table" and "deleting all records" from a
table?
What are the Large object types suported by Oracle?
Difference between a "where" clause and a
"having" clause ?
What's the difference between a primary key and a unique
key?
What are cursors? Explain different types of cursors. What
are the disadvantages of cursors? How can you avoid cursors?
What are triggers? How to invoke a trigger on demand?
What is a join and explain different types of joins.
What is a self join?
What is SQL?
SQL stands for 'Structured Query Language'.:
What is SELECT statement?
The SELECT statement lets you select a set of values from a
table in a database. The values selected from the database table would depend
on the various conditions that are specified in the SQL query.
How can you compare a part of the name rather than the
entire name?
SELECT * FROM people WHERE empname LIKE '%ab%' Would return
a recordset with records consisting empname the sequence 'ab' in empname .
What is the INSERT
statement?
The INSERT statement lets you insert information into a
database.
How do you delete a record from a database?
Use the DELETE statement to remove records or any particular
column values from a database.
How could I get distinct entries from a table?
The SELECT statement in conjunction with DISTINCT lets you
select a set of distinct values from a table in a database. The values selected
from the database table would of course depend on the various conditions that
are specified in the SQL query. Example
SELECT DISTINCT empname FROM emptable
How to get the results of a Query sorted in any order?
You can sort the results and return the sorted results to
your program by using ORDER BY keyword thus saving you the pain of carrying out
the sorting yourself. The ORDER BY keyword is used for sorting.
SELECT empname, age, city FROM emptable ORDER BY empname
How can I find the total number of records in a table?
You could use the COUNT keyword , example
SELECT COUNT(*) FROM emp WHERE age>40
What is GROUP BY?
The GROUP BY keywords have been added to SQL because
aggregate functions (like SUM) return the aggregate of all column values every
time they are called. Without the GROUP BY functionality, finding the sum for
each individual group of column values was not possible.
What is the difference among "dropping a table",
"truncating a table" and "deleting all records" from a
table.
Dropping : (Table
structure + Data are deleted),
Invalidates the dependent objects ,Drops the indexesTruncating: (Data alone deleted), Performs an automatic
commit, Faster than delete
Delete : (Data alone deleted), Doesn’t perform automatic
commit
What are the Large object types suported by Oracle?
Blob and Clob.
Difference between a "where" clause and a
"having" clause.
Having clause is used only with group functions whereas
Where is not used with.
What's the difference between a primary key and a unique
key?
Both primary key and unique enforce uniqueness of the column
on which they are defined. But by default primary key creates a clustered index
on the column, where are unique creates a nonclustered index by default.
Another major difference is that, primary key doesn't allow NULLs, but unique key
allows one NULL only.
What are cursors? Explain different types of cursors. What
are the disadvantages of cursors? How can you avoid cursors?
Cursors allow row-by-row prcessing of the resultsets.
Types of cursors: Static, Dynamic, Forward-only,
Keyset-driven. See books online for more information.
Disadvantages of cursors: Each time you fetch a row from the
cursor, it results in a network roundtrip, where as a normal SELECT query makes
only one rowundtrip, however large the resultset is. Cursors are also costly
because they require more resources and temporary storage (results in more IO
operations). Furthere, there are restrictions on the SELECT statements that can
be used with some types of cursors.
Most of the times, set based operations can be used instead
of cursors.
What are triggers? How to invoke a trigger on demand?
Triggers are special kind of stored procedures that get
executed automatically when an INSERT, UPDATE or DELETE operation takes place
on a table.
Triggers can't be invoked on demand. They get triggered only
when an associated action (INSERT, UPDATE, DELETE) happens on the table on
which they are defined.
Triggers are generally used to implement business rules,
auditing. Triggers can also be used to extend the referential integrity checks,
but wherever possible, use constraints for this purpose, instead of triggers,
as constraints are much faster.
What is a join and explain different types of joins.
Joins are used in queries to explain how different tables
are related. Joins also let you select data from a table depending upon data
from another table.
Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER
JOINs are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL
OUTER JOINS.
What is a self join?
Self join is just like any other join, except that two
instances of the same table will be joined in the query.
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