There are exercises on SELECT statement (presently 139 exercises on learn stage and 224 exercises on rating stages) and on other
data manipulation operators - INSERT, UPDATE, DELETE (30 exercises).
The rating of members is carried on SELECT exercises. See test conditions.
The book "SQL. Problems and solutions" , which is analyzing the characteristic mistakes admitted at the solution of the learn-stage exercises on the site, was originally published in Peter Publishing Company.
Today we have 828 visitors (104 new). 55 exercises solved (23 on SELECT and 32 on DML),
on learning stage - 1533
Practical skills of SQL language
This site will help everyone to gain or improve skills in building
SQL Data Manipulation Language statements. To train You will have to build yourself
the SQL statements for retrieval or modification of specific data required in the exercises.
When Your query is incorrect, You will be able to see rows returned by the correct
query along with that returned by Your query. Furthermore, you may execute arbitrary
DML statements on available databases by setting the "Without checking" option. There are
five levels of difficulty (from 1 to 5), You may see it in second column of
exercises list. We propose the exercises on retrieving data (SELECT statement) and
the exercises on modifying data (INSERT, UPDATE, and DELETE statements). Your success in the solving the exercises are shown by a rating of participants.
As this takes place, there are three stages:
the first one (first 9 exercises) is performed without time control for an individual
exercise, the second one (begins with the exercise #10) controls time for completion of each
task. At the third stage which refers to optimizing and begins with exercise #139, it is required not only to solve an exercise correctly, but also time of execution of inquiry should be commensurable with time of execution of the author's solution.
Exercises of the first stage are available without registration and may be solved
in any order You like. The solution of the rest of exercises requires registration.
REGISTRATION IS FREE as this for all other services of the site. In the third column of exercises list You
will be able to see ("OK") notes with the numbers of done exercises, but that
is available only to the registered users. In fact, that is the main reason for registration.
If You would like to visit our web site again, You won't have to recollect which
exercises You have done already and which You haven't. If You don't want to register,
You may enter as a guest, but in that case Your results won't
be traced by the system. Registered users also may discuss the solutions to exercises in our forum.
NOTE: The query stated incorrectly may return the "correct" data on a current state of database.
For this reason You should not be surprised if the results of incorrect query are
coincide with the results of right one with Your query is estimated as incorrect by the Verifying system.
User's queries are executed by SQL server that brings some limitations to the
syntax of SQL statements. Now we use Microsoft SQL Server 2012 on the rating stages,
and MySQL 5.5.11, PostgreSQL 9.0, and Oracle Database 11g on the learn stage in addition. That is why You should follow
the syntax of these realizations when building queries. It should be noted that SQL syntax,
implemented in Microsoft SQL Server, is close to that of SQL-92 standard. But there are some
distinctions, among them is absence of NATURAL JOIN of tables. Supplied help on SQL Data Manipulation Language is held in accordance
with SQL-92 standard and contains information necessary for solving the exercises. In the same place it is possible to find features of used realization (SQL Server 2005).