SQL Function Cheatsheet | Notion

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Syntax can vary slightly by engine (Postgres, MySQL, BigQuery, Snowflake). These are the widely supported forms; check your engine's docs for edge cases.

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Aggregate functions

Function	What it does
`COUNT()`	Counts rows (`COUNT(*)` counts all rows, `COUNT(column)` skips nulls)
`SUM()`	Adds up numeric values
`AVG()`	Calculates the mean
`MIN()` / `MAX()`	Finds the smallest or largest value
`GROUP BY`	Groups rows so aggregate functions apply per group, not the whole table

Window functions

Function	What it does
`ROW_NUMBER()`	Numbers each row within a partition, no ties
`RANK()`	Ranks rows within a partition, with gaps after ties
`DENSE_RANK()`	Ranks rows within a partition, without gaps after ties
`LAG()`	Looks at the value from a previous row
`LEAD()`	Looks at the value from a following row
`NTILE(n)`	Splits rows into n roughly equal buckets
`OVER (PARTITION BY ... ORDER BY ...)`	Defines the window a function operates across

String functions

Function	What it does
`CONCAT()`	Joins strings together
`SUBSTRING()`	Extracts part of a string
`TRIM()`	Removes leading and trailing whitespace
`UPPER()` / `LOWER()`	Changes case
`REPLACE()`	Swaps one substring for another
`LENGTH()`	Returns the number of characters

Date and time functions

Function	What it does
`CURRENT_DATE` / `NOW()`	Returns today's date or the current timestamp
`DATE_TRUNC()`	Rounds a date down to a unit (day, month, year)
`DATEDIFF()`	Calculates the difference between two dates
`EXTRACT()`	Pulls out a specific part of a date (year, month, day)

Conditional logic

Function	What it does
`CASE WHEN ... THEN ... ELSE ... END`	Inline if/else logic in a query
`COALESCE()`	Returns the first non-null value in a list
`NULLIF()`	Returns null if two values are equal, otherwise the first value

Query structure

Clause	What it does
`WITH <name> AS (...)`	Defines a common table expression (CTE) to reference later in the query
`INNER JOIN`	Returns rows with a match in both tables
`LEFT JOIN`	Returns all rows from the left table, matched where possible
`UNION`	Combines results from two queries, removing duplicates (`UNION ALL` keeps them)