Structured Query Language (SQL)

The BEC exam focuses on using Structured Query Language (SQL) to access important information in a database.

SQL Queries

SQL queries are statements used to interact with a database. They allow users to retrieve, insert, update, or delete data, making SQL an integral part of managing and manipulating databases.

Examining SQL Queries

To ensure that a standard SQL query retrieves a relevant and complete data set, it’s important to examine several components of the query. These include commands, clauses, operators, aggregate functions, and string functions.

Commands

SQL commands are instructions used to interact with the database and retrieve data. The most common SQL commands include:

• SELECT: Used to select data from a database.

• FROM: Used to specify the table from which to retrieve data.

• WHERE: Used to filter the results.

• GROUP BY: Used to group rows that have the same values in specified columns into aggregated data.

• ORDER BY: Used to sort the result-set in ascending or descending order.

• HAVING: Used with the GROUP BY clause to filter group results.

Clauses

SQL clauses are used to refine and format the data that a SQL query returns. Common SQL clauses include:

• WHERE: Used to filter records based on one or more conditions.

• GROUP BY: Used to group rows with similar values into aggregated data, like summation, averaging, counting, or getting the minimum or maximum result.

• ORDER BY: Used to sort the results in ascending or descending order based on one or more columns.

• HAVING: Used to filter result sets that are generated by the GROUP BY clause.

Operators

SQL operators are used to perform comparisons or logical operations. Common SQL operators include equal to, not equal to, greater than, and less than.

Aggregate Functions

SQL aggregate functions perform calculations on a set of values and return a single value.

Common SQL aggregate functions include:

• COUNT(): Returns the number of rows that match a specified criteria.

• SUM(): Returns the total sum of a numeric column.

• AVG(): Returns the average value of a numeric column.

• MAX(): Returns the highest value in a set of values.

• MIN(): Returns the lowest value in a set of values

String Functions

SQL string functions are used to manipulate and analyze text data. Common SQL string functions include:

• CONCAT(): Concatenates two or more strings into one string.

• SUBSTR() or SUBSTRING(): Extracts a substring from a string (starting at any position).

• REPLACE(): Replaces all occurrences of a substring within a string, with another substring.

• LENGTH(): Returns the length of a string