Creates an index
of a column or group of columns within a table. An index essentially
functions as an ordered list (alphabet or numeric) that provides
a fast and efficient way to look up records. If a UNIQUE index
is specified, this indicates an index that does not allow duplicate
values. Now, let’s focus on some SQL basic commands that one should know when they start learning about SQL. There are many queries that seem to be basic, but I have covered few that are really essential for a beginner. For explaining all the query I have considered the Student table, which I will be using.
You can add or omit the keyword ASC to sort the output in ascending order. Now, we need to show only employees with a salary above 3,800. It’s a clause that accepts conditions and is used for filtering the output. It goes through the table and returns only the data that satisfies the condition.
Installation and Setup
Then we add each column from the table quarterly_sales showing the quarterly sales and name it total_sales_2022. Each column in SELECT also has the table alias before it, with the alias and the column name separated by a dot. It is used to specify the columns on which the two tables will be joined.
Most websites use databases to store user data, and many developers use SQL to interact with the information they collect. If there is a table with dozens of columns but only five columns need to be accessible, simply create a view for the end-user to present these five columns only. Views show only specific parts of the data selected by the user. First, select the column department from the table employees. As we want to add the salary values, we specify the column salary in the function.
Database developer
You can do that using comparison operators in the WHERE clause. This query is useful when selecting two (or more) columns from one table. This query is useful when you want to quickly get all the columns from a table without basis sql writing every column in the SELECT statement. We’ll introduce the dataset, and then we’re off to writing and explaining basic SQL queries. This feature requires that object level permissions
be enabled on the database.
With our online SQL editor, you can edit the SQL statements, and click on a button to view the result. The following defines the SQL grammar for SQL statements supported by
the BASIS DBMS. SQL reserved words are written in upper case to make them
more readily identifiable. For detailed list of BBj’s support of these specifications, refer to
BBj
Support for SQL-99 and SQL-2003 Features.
SQL — Grammar
At runtime, the SQL engine uses this information to determine which key to use for iteration. For example, assume there is a key on the LAST_NAME column in a table and one on the STATE column. Now assume that all people in the table live in New Mexico, Colorado, or Texas. Also, assume that most of the people do not have the same last name.
Then comes the comparison operator, and after that, the value that the data has to be greater than. This condition will now return all the salaries that are above 3,800. However, this time, instead of an asterisk, we write the specific column name in SELECT. All this tells us that this table is a list of a company’s employees and their salaries.
By default, the user provides values for
all columns in the record in the order they are defined. A role is a security group that groups together
one or more users making it easier to assign privileges to multiple
users. This feature requires that object level permissions be
enabled on the database. This training will help you understand MySQL in-depth and help you achieve mastery over the subject. We can increase the accuracy and reliability of data that goes into the database through a table with the help of the concept called SQL CONSTRAINTS. These constraints make sure that there is no violation in terms of a transaction of data if found then the action will be terminated.
- From here we can just type in the query we want to run and we will see the data returned in our terminal window.
- In SQL we use the NULL term to represent a missing value.
- For example, a view may look at the customer table, but only display the customer last name and the customer first name fields.
- An alternative to using the terminal is to connect to the SQLite database via Python.
To answer the first two of these questions, we can include the table names for each column in our SELECT command. The way we do this is simply to write the table name and column name separated by a .. For example, instead of SELECT order_number, name we would write SELECT orders.order_number, customers.name. Adding the table names here helps the database to find the columns we’re looking for by telling it which table to look in for each. ORDER BY statement helps us to sort the data according to the specified column. The result set of
the data can be sorted either ascending or descending.