For details about the syntax of window function calls, see Window function calls.

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General-purpose window functions

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row_number()

The row_number() function assigns a unique sequential integer to each row within a partition of a result set. The numbering starts at 1 for the first row in each partition and increments by 1 for each subsequent row. row_number() can be used to turn non-unique rows into unique rows. This could be used to eliminate duplicate rows. The syntax of row_number() is: 
row_number() → integer
We recommend using row_number() only for top-N pattern queries. For details about this pattern, see Top-N by group.

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rank()

rank() returns the rank of the current row, with gaps; that is, the row_number of the first row in its peer group. The syntax of rank() is: 
rank() → integer

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dense_rank()

dense_rank() returns the rank of the current row, without gaps; that is, if some rows share the same rank, the row next to them is assigned the next consecutive rank. The syntax of dense_rank() is: 
dense_rank() → integer

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lag() and lead()

lag() allows you to access the value of a previous row in the result set. You can specify the number of rows to look back. The syntax of lag() is: 
lag ( value anycompatible [, offset const integer] ) → anycompatible
lead() is similar to lag(), but it allows you to access the value of a subsequent row in the result set. The syntax of lead() is: 
lead ( value anycompatible [, offset const integer] ) → anycompatible

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first_value() and last_value()

The first_value() function returns the value of the first row in the current window frame. The syntax of first_value() is: 
first_value ( value anyelement ) → anyelement
last_value() returns the value of the last row in the current window frame. The syntax of last_value() is: 
last_value ( value anyelement ) → anyelement

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Aggregate window functions

All aggregate functions, including builtin ones such as sum() and min(), user-defined ones and AGGREGATE:-prefixed scalar functions, can be used as window functions. For the complete list of builtin aggregate functions and their usage, see Aggregate functions.