Learn SQL Queries

Explore the from clause and how to pull records from one or more tables, then learn how inner and left joins connect related data efficiently.

Learn how to query related data from two tables using inner join and left join, and why using on conditions with a where clause ensures correct matches.

Learn how to perform an inner join between employees and departments, selecting employees' first and last names and the department name, using alias prefixes to avoid ambiguity.

Learn how a left join combines all employees with their departments, returning matching department data where available and including all employee records.

Explore the difference between left join and inner join in SQL by linking the employees and department tables with primary and foreign keys, showing matches and unmatched left rows.

We compare left join and right join, showing how they produce the same results when switching table order, and how inner joins differ by returning only matching records.

Perform an inner join using a temp table with employees and departments, selecting first name, last name, and the full department name.

Learn how to perform an inner join with a table variable to connect employee and department data, declare and populate the variable, and select from it instead of real tables.

Learn how to build union queries in T-SQL to combine employee data from different databases, align fields, optionally concatenate names, and display salaries from highest to lowest.

Explore using the where clause to filter records in SQL queries. Apply operators equals, less than, greater than, between, and in, and combine conditions with and, or, and parentheses.

Learn how to use the equals operator to filter employees by numeric and text fields, wrap text in single quotes, and preview simple joins.

Learn to filter salary data in SQL Server using comparison operators—greater than, less than, equals, greater than or equal to, less than or equal to—and the between range to write concise queries.

Learn how to filter records using the IN operator in SQL, selecting departments 3 or 4 from the employee table and handling text with single quotes.

Learn to use the between keyword to define a range, such as salary between 98 and 110, for clearer and more concise SQL queries.

Explore using in and not in with a sub query on the Acme database, selecting employees by department and applying dynamic not in examples to filter results.

Explore the difference between using the in clause and a subquery to filter employees by department, highlighting dynamic lookups versus hard-coded values for robust sql querying.

Explore using the where and operator with the datepart function to filter employees by hire year, and combine department and year conditions for readable sql queries.

Examine how the or operator differs from and in SQL Server, using datepart to extract years, filtering employees by department or hire year, and understanding when or expands results.

Sort customer data with order by using ordinals or field names to group by state and city, then order by name, and learn ordinals, default ascending, and common pitfalls.

Ordering by ordinals saves typing, but altering the select list or removing fields can break the sort or cause out-of-range errors. Use ordinals only for permanent fields or dropdown data.

Learn how to use the descending keyword to sort results, see examples sorting by state, and apply order by to view newest records or per-department salary rankings.

Learn how to order results with an order by case expression to prioritize New York records in a single query, contrasting simple two-query methods with a more efficient approach.

Learn how the group by clause uses aggregate functions like min, max, and count to summarize customers by last name and their largest order total.

Grouping by last name consolidates data and enables you to compute max total and min total, then derive the spread for quick reports.

Explore the count function with group by to tally records per customer last name in the sales order table, and order results by the second field.

Apply the sum function to a query, add a sum field, show total dollar amount and record counts, and order customer names by the sum field in descending order.

Learn to use sql's average function with group by to compute per-customer averages, alongside sum and count, for financial reports.

Explore how to use group by with the having clause to filter aggregated results, such as showing customers who spent over $2000 or exceeded sales counts.

Master group by and having to sum the total field and filter customers with total greater than or equal to 2000, and compare having with group by and order by.

Stored procedures populate dropdowns and keep sql logic centralized, avoiding code changes. Filter visible = 1 to hide inactive customers, updating the dropdown without recompiling client applications.

Discover user defined functions in SQL, name and call them with parameters, and see text manipulation examples like concatenation and leading zero padding used for sample IDs.

Learn to use a user defined function in a real-world sql example, including scalar valued functions, owner qualification, and a prepared function that pads order numbers to six digits.