14.20.5 Window Function Restrictions

The SQL standard imposes a constraint on window functions that they cannot be used in UPDATE or DELETE statements to update rows. Using such functions in a subquery of these statements (to select rows) is permitted.

MySQL does not support these window function features:

• DISTINCT syntax for aggregate window functions.

• Nested window functions.

• Dynamic frame endpoints that depend on the value of the current row.

The parser recognizes these window constructs which nevertheless are not supported:

• The GROUPS frame units specifier is parsed, but produces an error. Only ROWS and RANGE are supported.

• The EXCLUDE clause for frame specification is parsed, but produces an error.

• IGNORE NULLS is parsed, but produces an error. Only RESPECT NULLS is supported.

• FROM LAST is parsed, but produces an error. Only FROM FIRST is supported.

A maximum of 127 windows is supported for a given SELECT. Note that a single query may use multiple SELECT clauses, and each of these clauses supports up to 127 windows. The number of distinct windows is defined as the sum of the named windows and any implicit windows specified as part of any window function's OVER clause. You should also be aware that queries using very large numbers of windows may require increasing the default thread stack size (thread_stack system variable).