如何在PostgreSQL中提取表的唯一列的名称？

Question

假设我在PorstreSQL中有一个表定义为：

CREATE TABLE my_table (
  id serial not null primary key,
  var1 text null,
  var2 text null unique,
  var3 text null,
  var4 text null unique
);

是否有对information_schema的查询，仅提供唯一列的名称？理想的响应应该是：

var2
var4

查询应一起忽略多个列的唯一键。

Answer 1

您需要information_schema.table_constraints和information_schema.constraint_column_usage：

SELECT table_schema, table_name, column_name
FROM information_schema.table_constraints AS c
   JOIN information_schema.constraint_column_usage AS cc
      USING (table_schema, table_name, constraint_name)
WHERE c.constraint_type = 'UNIQUE';

如果要跳过多于一列的约束，请使用分组：

SELECT table_schema, table_name, min(column_name)
FROM information_schema.table_constraints AS c
   JOIN information_schema.constraint_column_usage AS cc
      USING (table_schema, table_name, constraint_name)
WHERE c.constraint_type = 'UNIQUE'
GROUP BY table_schema, table_name
HAVING count(*) = 1;