教你PostgreSQL数据库如何删除check约束的实现
删除check约束：
1.\d table_name 查找约束名称
\d dm_alarms_fct_20170613
“dm_alarms_fct_20170613_dm_transct_date_key_check”
2.alter table .. drop constraint ..
ALTER TABLE “dm_alarms_fct_20170613” Drop constraint “dm_alarms_fct_20170613_dm_transct_date_key_check”;
补充：PostgreSQL查询约束和创建删除约束
查询约束constraint
SELECT
tc.constraint_name, tc.table_name, kcu.column_name,
ccu.table_name AS foreign_table_name,
ccu.column_name AS foreign_column_name,
tc.is_deferrable,tc.initially_deferred
FROM
information_schema.table_constraints AS tc
JOIN information_schema.key_column_usage AS kcu ON tc.constraint_name = kcu.constraint_name
JOIN information_schema.constraint_column_usage AS ccu ON ccu.constraint_name = tc.constraint_name
WHERE constraint_type = ‘UNIQUE’ AND tc.table_name = ‘table_name’;
constraint_type有四种：
UNIQUE、PRIMARY KEY、CHECK、FOREIGN KEY, 通过修改上边sql语句的table_name和constraint_type来进行相应的查询。
添加约束
ALTER TABLE table_name ADD CONSTRAINT uk_users_name1 UNIQUE (NAME);
删除约束
alter table table_name drop constraint if EXISTS uk_users_name1;
以上为个人经验，希望能给大家一个参考，也希望大家多多支持。如有错误或未考虑完全的地方，望不吝赐教。
