如何在 PostgreSQL 中提取表的唯一列的名稱？

Question

假設我在 PorstreSQL 中有一個表定義為：

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

是否有對information_schema的查詢僅提供唯一列的名稱？ 理想的反應應該是：

var2
var4

查詢應該一起忽略多個列的唯一鍵。

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';

如果要跳過多列的約束，請使用分組：

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;