SQL Queries 101: A Beginner's Guide to Data Retrieval

Explore using SQLite online as a no install alternative to SQL Server, learn to sign in, create an account, and import flat files for customers, district, orders, and complaints.

Run a simple sql query to return all columns and rows from the customer table using select star, and execute it with a semicolon in sql server management studio.

Select only the needed columns from a table, use aliases with as and quotes for spaces, format long queries with line breaks, and end with a semicolon.

Learn how to fetch top or bottom rows from a table using top, and how to obtain bottom rows by ordering by client ID in descending order.

Extract distinct values from a table using the distinct keyword, illustrated with district id and ordering by district id to reveal unique districts.

Discover how the order by clause sorts query results, using district and first name examples to illustrate ascending and descending orders and sorting with multiple levels via commas.

Learn how to use concat and delimiters to combine first name and last name into a full name, with options for middle name and separators, in SQL queries 101.

Explore using left and right text functions to extract a specified number of characters from a column, such as the last three of an ssn, treating data as text.

Use the Len function to calculate the total character length, including spaces, for a column or the full name, and apply length checks for IDs.

Learn how the format function in sql formats birth dates, currencies by region, and percentages, with practical examples and varied formatting options.

Learn to use aggregates and grouping in SQL on the orders table, mastering sum, min, max, count, and currency formatting to produce a single-row summary of sales, quantity, and orders.

Learn how the group by clause adds detail to aggregates, returning one row per segment or category by grouping non-aggregate columns and using order by to structure results.

Use the date difference function in SQL to compute age from a birth date, using interval year, start date, end date as current date, and alias as age.

Learn to convert strings to dates in SQL Server, build dates from parts, and extract year, month, and day using format and other date functions.

Master comparison and logical operators in SQL, using the where clause to filter by quantity greater than five, optionally with and, order by, and dynamic aggregates.

Learn to use SQL logical operators, focusing on between and the alternative of using >= and <= to filter orders by quantity between five and ten.

Learn how the like operator enables pattern matching in SQL, using % as a wildcard to find product names containing or starting with printer.

Learn how to filter data using or and in SQL, comparing readability and efficiency when querying the orders table for subcategories such as paper and art.

Explore the remaining logical operators, such as all, any, exists, and some, and connect them to table relationships; revisit after studying customer and orders tables.

Use the having clause after group by to filter aggregated results, such as count of order_id greater than 500, instead of where.

Explore partition by using the over clause to compute min and max age per district id, while observing the default ordering of partitioned results.

Explore inner joins in SQL by linking the customer and district tables on district id and district code, using venn-diagram intuition to retrieve region, state, and city details.

Explore inner joins on orders and complaints to fetch only linked records, selecting key fields from both tables and illustrating how complaints relate to orders.

Learn how left joins return all orders with matching complaints or nulls for none, contrast with inner joins, and switch to right joins to emphasize the right table.

Learn how to join three tables in SQL by combining orders, complaints, and customers using inner and left joins, with attention to linking on the client ID and alias usage.

Join four tables: orders, complaints, customer, and district, using district code to reveal city data. Compare inner and left joins and understand nulls when no complaints exist.

Learn how the full outer join reveals all records from both tables, including unmatched rows with nulls, to merge unrelated data and reveal discrepancies.

Learn how to use the SQL except clause to subtract rows, combining left join and inner join to return orders without complaints.

Use exists with a subquery to retrieve only products or orders that have related complaints, reducing duplication from multiple complaints and focusing on relevant data.

Learn to use subqueries to fetch orders before any complaints are registered. Compare approaches using min(date_received) and the all operator to achieve the same result.