What is a Database Query?
In common language, a query is a request for information. A database is a repository of information where organizations store, access, write, and delete data. Thus, a database query is a request for information from the database written in syntax.
Queries help Database Administrators (DBAs) or other users access data from a database management system (DBMS) where information is organized in tables or collections of related data.
A query retrieves and presents this data in human-readable forms like tables, graphs, and pictorials. A database query is a communication code between a user and a machine. The query helps the machine understand the command and perform the specific action. There are various database query languages to write a query.
What’s the Common Database Query Language?
Creating, accessing, and manipulating data on a database requires giving instructions in a programming language called query language. SQL (Structured Query Language) is the oldest and most prominent query language.
SQL code snippets called queries can access, manage, and manipulate data in a relational database management system (RDBMS) where data is organized and structured into various relational groups.
The SQL input commands are simple, similar to the English language sentences. For example, a simple SQL command, SELECT column1 FROM my_table, will select the specified column from the specific table.
There are some other query languages for database communication:
- SQL
- Datalog
- DMX
- XQuery
- GraphQL
Performing a Database Query
Performing a database query involves several steps. The following is how to perform a database query using SQL commands.
Identifying the Objective
Before writing a query, the DBA or the user must clearly define what information to retrieve or manipulate from the database. This could involve selecting specific data from tables, updating existing records, or performing calculations.
Writing the Query
After identifying the objective, writing a query is the next step. There are many SQL commands to construct a query.
Some essential commands are:
- SELECT: Use this command to retrieve data from one or more tables.
- INSERT: This command adds new records to a table.
- UPDATE: It is to modify existing records in a table.
- DELETE: The command removes records from a table quickly. It enables setting the criteria for data deletion from a table.
- CREATE TABLE: This command helps create a new table in the database.
- ALTER TABLE: Use this command to modify the structure of an existing table.
- DROP TABLE: To delete a table entirely from the database, use the DROP TABLE command.
- PARAMETER: The command enables setting criteria for selecting data records.
Executing the Query
The next process after writing the query is executing it against the database. The DBA or the user can use the database client tool’s interface or execute SQL statements in a programming language such as Python, Java, or PHP for query execution.
Retrieving and Interpreting Results
After executing the query, review the results returned by the database. The results must match the expectations. If not, interpret the query and look for anomalies.
Handling Errors and Refining the Query
If the query doesn’t produce the expected results or errors appear, reviewing and modifying it is essential. It is known as query optimization. Reviewing the SQL syntax, database schema, and query logic will help address any issues with the query.
Testing
Test the optimized queries thoroughly to ensure they produce the desired results under various conditions. By observing the testing results, iterate the queries to get optimal performance.
Database Query Optimization
Wrong or inefficient database queries are the most common reason for the poor performance of a DBMS. They reduce system response time, increase the use of server resources, and make the DBMS ineffective.
To improve database performance, optimizing queries is essential. There are many ways to optimize queries. But, optimizing every query is unnecessary and tedious. The DBA must be selective.
The best way to select which query to optimize is to look at the query’s execution plan and server resource utilization and compare historical data with established baselines.
Some ways to database query optimization are:
- Using indexes
- Minimizing subqueries
- Caching
- Proactive query performance monitoring