postgresql - 修改postgresql中的UNIQUE

Question

我有一张像这样的 table

        CREATE TABLE IF NOT EXISTS link_data (
            id                  UUID PRIMARY KEY DEFAULT uuid_generate_v4(),
            connection_id UUID NOT NULL,
            the_link TEXT NOT NULL,
            UNIQUE (connection_id, the_link),
            FOREIGN KEY (connection_id)
              REFERENCES connection(id)
              ON DELETE CASCADE
        );

我需要修改表，使其仅在connection_id上是唯一的，即UNIQUE (connection_id) 如何更改表来实现此目的？

Answer 1

首先将其放在:

ALTER TABLE link_data 
DROP CONSTRAINT constraint_name;

然后:

ALTER TABLE link_data 
ADD CONSTRAINT constraint_name UNIQUE (connection_id);

您可以通过以下方式检查表约束:

SELECT con.*
       FROM pg_catalog.pg_constraint con
            INNER JOIN pg_catalog.pg_class rel
                       ON rel.oid = con.conrelid
            INNER JOIN pg_catalog.pg_namespace nsp
                       ON nsp.oid = connamespace
       WHERE nsp.nspname = '<schema name>'
             AND rel.relname = 'link_data ';