|SQL exercises||February 23, 21:21 MSK|
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, DELETE, and MERGE 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 8 exercises) is performed without time control for an individual
exercise, the second one (begins with the exercise #9) 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.
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.
Successful testing of yours can be confirmed by the certificate "SQL Data Manipulation Language Specialist". We support quality of our certificate by periodically replacing exercises and changing the certificate requirements.
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).