SQL query examples

Ready-to-copy SQL for the queries developers look up most — each with the code across PostgreSQL, MySQL, SQL Server, and SQLite, plus a plain-English explanation of how it works.

Need a query for your own schema? Describe it in plain English with the AI SQL Generator →

Ranking & top-N

Find the second highest value

Get the second largest value in a column (e.g. the second highest salary).

Find the Nth highest value

Get the Nth largest value in a column using DENSE_RANK.

Number and rank rows

Add a sequential number or rank to rows with window functions.

Get the top N rows per group

Return the highest N rows within each group (greatest-n-per-group).

Grouping & aggregation

Count rows per group

Count how many rows fall into each category with GROUP BY.

Group by month

Summarize rows per calendar month from a date or timestamp column.

Calculate a running total

Compute a cumulative sum that grows row by row.

Pivot rows into columns

Turn row values into columns using conditional aggregation.

Finding & removing duplicates

Find duplicate rows

Find rows that share the same value in one or more columns.

Delete duplicate rows (keep one)

Remove duplicate rows while keeping a single copy of each.

Joins & set operations

Find rows not in another table

Return rows from one table that have no match in another (anti-join).

Dates & time

Get the days between two dates

Compute the difference in days between two date columns.

Get rows from the last 30 days

Filter rows whose timestamp falls within the last 30 days.

Modifying data

Update a table from another table

Update rows using values looked up from a second table (UPDATE with JOIN).

Insert or update (upsert)

Insert a row, or update it instead when a key already exists (upsert).