**Basic Syntax:**

```sql

FUNCTION() OVER (PARTITION BY column1 [, column2, ...])

```

**Complete Window Specification:**

```sql

FUNCTION() OVER (

PARTITION BY column1, column2

ORDER BY column3 DESC

ROWS BETWEEN UNBOUNDED PRECEDING AND CURRENT ROW

)

```

**Named Window:**

```sql

SELECT ... FUNCTION() OVER window_name ...

WINDOW window_name AS (PARTITION BY column ORDER BY column)

```

PARTITION BY divides rows into logical groups without collapsing them

Optional clause - omit for calculations across all rows

Can partition by multiple columns: PARTITION BY col1, col2, col3

Supports expressions: PARTITION BY EXTRACT(year FROM date)

Each partition is processed independently by the window function

Order of columns in PARTITION BY affects grouping granularity

Full support for PARTITION BY, named windows, and all window functions. Excellent optimization.

Full support starting MySQL 8.0. Earlier versions lack window functions entirely.

Full support with excellent performance optimization. OVER clause well-optimized.

Comprehensive support with advanced analytical functions. Pioneer in window functions.

Core references in this topic include WHERE, AND, BETWEEN. Learn what each one does, when to use it, and the execution or engine rules that matter.

WHERE

Filters rows before projection and sorting. It decides which rows continue through the query pipeline.

SELECT ... FROM table WHERE condition;

Most performance issues start with a weak WHERE clause or a missing supporting index.

AND

Requires every condition in the boolean expression to evaluate to TRUE.

condition_a AND condition_b

AND has higher precedence than OR.

BETWEEN

Checks whether a value falls inside an inclusive lower/upper range.

order_total BETWEEN 100 AND 500

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