select cast (2000 as type of quint) from rdb$database select cast (2000 as int) from rdb$database.
select a,b,null,null from table1 union select null,null,c,d from table2 union select null,null,null,null,e,f from table3.
select number, text from test_table union select number, text from test_table_2. Как Вы видите, вывелось всего 5 строк, так как у нас первая строка в первом запросе и первая строка во втором запросе одинаковые, поэтому они объединились. Теперь давайте объединим через union all.
ru.wikipedia.org. Применение UNION ALL дает ...
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Union select null, null, null, null, null, null, null from information_schema.tables.
UNION ALL Syntax. The UNION operator selects only distinct values by default. To allow duplicate values, use UNION ALL: SELECT column_name(s) FROM table1 UNION ALL SELECT
Each SELECT statement within the UNION ALL must have the same number of fields in the result sets with similar data types. What is the difference between UNION and UNION ALL?
You can mix UNION ALL and UNION DISTINCT in the same query. Mixed UNION types are treated such that a DISTINCT union overrides any ALL union to its left. A DISTINCT union can be produced explicitly by using UNION DISTINCT or implicitly by using UNION with no following DISTINCT or ALL...
В данный момент у нас нет одинакового количества колонок, поэтому union надо использовать по-другому.