| `count` with `@distinct` over a tuple `x1, x2` | Postgres: `type: count_distinct`, `sql: 'ROW(x1, x2)'`, with one `filters` entry `x1 IS NOT NULL AND x2 IS NOT NULL`, so a tuple with a null component is not counted, as in the view. MySQL: the view's own `COUNT(DISTINCT x1, x2)` as a `type: number` measure (a condition `c` makes it `COUNT(DISTINCT CASE WHEN c THEN x1 END, x2)`); MySQL's multi-argument form skips a tuple with a null component and compares by the columns' collation, which a `JSON_ARRAY(x1, x2)` key does not: on mysql:8.4 under the default `utf8mb4_0900_ai_ci` it counted `'abc'` and `'ABC'` as two tuples where the view counts one |
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