[MDEV-19901] Wrong window function calculation - Jira

Consider this query:

with t(a, b) as (values (1, 1), (2, 1), (3, 2), (4, 2))

select

a,

  sum(a) over () b,

  sum(a) over (partition by b) c,

  sum(a) over (order by a rows between unbounded preceding and 1 preceding) d

from t

order by a;

The expected result is:

a|b |c|d|

-|--|-|-|

1|10|3| |

2|10|3|1|

3|10|7|3|

4|10|7|6|

The actual result is:

a|b |c|d|

-|--|-|-|

1|10|3|2|

2|10|3| |

3|10|7|3|

4|10|7|6|

This can be illustrated when not projecting column c, in case of which the problem goes away:

with t(a, b) as (values (1, 1), (2, 1), (3, 2), (4, 2))

select

a,

  sum(a) over () b,

  -- sum(a) over (partition by b) c,

  sum(a) over (order by a rows between unbounded preceding and 1 preceding) d

from t

order by a;

The result is now correct:

a|b |d|

-|--|-|

1|10| |

2|10|1|

3|10|3|

4|10|6|