Union in SQL
To combine the result of two SELECT statements, use UNION.
- The number and the order of the columns in the select list of both queries must be the same.
- The data types must be compatible.
- Duplicate rows will be dropped.
SELECT select_list_1
FROM table_expresssion_1
UNION
SELECT select_list_2
FROM table_expression_2
Source: https://www.postgresqltutorial.com/postgresql-union/
Examples
select 1 as n union select 2 as n;
n
---
1
2
select 1 as n union select 'a' as n;
ERROR: 22P02: invalid input syntax for integer: "a"
LINE 1: select 1 as n union select 'a' as n;
^