注：昨天我们已经基本上把PostgreSQL数据库的约束在创建表时的约束创建和查看约束过了一遍，今天我们着重关注于主键约束、外键约束、唯一约束和检查约束，看一下这四种重要约束的修改和删除操作。（结合PostgreSQL的系统表预先做好四种约束的启动和停止的准备）（作为对昨天内容的补充，约束的详细概念请见博客PostgreSQL的学习心得和知识总结（九）|PostgreSQL约束的定义创建及特性说明）
主键约束
| 主键约束 |
主键是用于在表中唯一标识行的列或列组。从技术上讲，主键约束是非空约束和UNIQUE约束的组合效果。
1、使用列约束设置主键
--说明：只能设置一列作为主键，主键默认名称为tablename_pkey。
uxdb=# create table test(uid serial primary key,uname varchar(50),upwd varchar(40));
CREATE TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+-----------------------------------
uid | integer | | not null | nextval('test_uid_seq'::regclass)
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_pkey" PRIMARY KEY, btree (uid)
如上，我们建立了一张表：表名test；并在字段uid建了主键（有了主键索引和主键约束）。
OK，我们下面来看一下数据库的系统表来得到一些我们想要的信息：
uxdb=# select * from ux_tables where tablename = 'test';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test | uxdb | | t | f | f | f
(1 row)
uxdb=# select oid from ux_class where relname='test';
oid
-------
16386
(1 row)
uxdb=# select contype,conname,conrelid from ux_constraint where conrelid=16386;
contype | conname | conrelid
---------+-----------+----------
p | test_pkey | 16386
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16386;
contype | conname | conrelid | conindid
---------+-----------+----------+----------
p | test_pkey | 16386 | 16390
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16386;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16390 | 1 | t | t | t | t
(1 row)
uxdb=#
- 表的oid为16386
- 从约束表ux_constraint里面得到约束名字叫做test_pkey；类型是p 就是主键索引；索引oid是16390
- 从索引表ux_index里面得到（依次）：索引oid、索引作用的列数、是唯一索引、是主键索引、索引对查询有效、索引还活着
2、使用表级约束设置主键
--说明：使用[表]级约束设置主键，可以设置一列或多列作为主键，主键默认名称为tablename_pkey，constraint myp_key_test2可省略。
uxdb=# create table test2(uid serial ,uname varchar(50),upwd varchar(40),constraint myp_key_test2 primary key(uid));
CREATE TABLE
uxdb=# \d test2
Table "public.test2"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+------------------------------------
uid | integer | | not null | nextval('test2_uid_seq'::regclass)
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"myp_key_test2" PRIMARY KEY, btree (uid)
uxdb=# select * from ux_tables where tablename = 'test2';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test2 | uxdb | | t | f | f | f
(1 row)
uxdb=# select oid from ux_class where relname='test2';
oid
-------
16394
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16394;
contype | conname | conrelid | conindid
---------+---------------+----------+----------
p | myp_key_test2 | 16394 | 16398
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16394;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16398 | 1 | t | t | t | t
(1 row)
uxdb=#
--信息基本上和上面一样
3、通过修改表结构设置主键
--语法：alter table table_name add [constraint constraint_name] primary key(column_1, column_2);
--说明：通过修改表结构设置主键，可以设置一列或多列作为主键，可以指定主键名称。
uxdb=# create table test3(uid serial ,uname varchar(50),upwd varchar(40));
CREATE TABLE
uxdb=# \d test3
Table "public.test3"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+------------------------------------
uid | integer | | not null | nextval('test3_uid_seq'::regclass)
uname | character varying(50) | | |
upwd | character varying(40) | | |
uxdb=# alter table test3 add constraint myp_key_test3 primary key(uid);
ALTER TABLE
uxdb=# \d test3
Table "public.test3"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+------------------------------------
uid | integer | | not null | nextval('test3_uid_seq'::regclass)
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"myp_key_test3" PRIMARY KEY, btree (uid)
uxdb=# select * from ux_tables where tablename = 'test3';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test3 | uxdb | | t | f | f | f
(1 row)
uxdb=# select oid from ux_class where relname='test3';
oid
-------
16402
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16402;
contype | conname | conrelid | conindid
---------+---------------+----------+----------
p | myp_key_test3 | 16402 | 16406
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16402;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16406 | 1 | t | t | t | t
(1 row)
uxdb=#
--这样的方式等同于把前面（一次创建OK）拆分了（分为先后两步）
4、往已有表添加自增的主键字段
--创建没有任何主键的表
uxdb=# create table test4(uname varchar(50),upwd varchar(40));
CREATE TABLE
uxdb=# insert into test4 values ("song1",123);
ERROR: column "song1" does not exist
LINE 1: insert into test4 values ("song1",123);
^
uxdb=# insert into test4 values ('song1','123');
INSERT 0 1
uxdb=# insert into test4 values ('song2','456');
INSERT 0 1
uxdb=# select * from test4;
uname | upwd
-------+------
song1 | 123
song2 | 456
(2 rows)
--我们要添加一个名为uid的自增主键到test4表
uxdb=# alter table test4 add column "uid" serial primary key;
ALTER TABLE
uxdb=# select * from test4;
uname | upwd | uid
-------+------+-----
song1 | 123 | 1
song2 | 456 | 2
(2 rows)
uxdb=# select oid from ux_class where relname='test4';
oid
-------
16408
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16408;
contype | conname | conrelid | conindid
---------+------------+----------+----------
p | test4_pkey | 16408 | 16414
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16408;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16414 | 1 | t | t | t | t
(1 row)
uxdb=# \d test4
Table "public.test4"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+------------------------------------
uname | character varying(50) | | |
upwd | character varying(40) | | |
uid | integer | | not null | nextval('test4_uid_seq'::regclass)
Indexes:
"test4_pkey" PRIMARY KEY, btree (uid)
uxdb=#
--和上面几种大同小异
5、删除主键约束
uxdb=# \d test4
Table "public.test4"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+------------------------------------
uname | character varying(50) | | |
upwd | character varying(40) | | |
uid | integer | | not null | nextval('test4_uid_seq'::regclass)
Indexes:
"test4_pkey" PRIMARY KEY, btree (uid)
uxdb=# alter table test4 drop constraint test4_pkey;
ALTER TABLE
uxdb=# \d test4
Table "public.test4"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+------------------------------------
uname | character varying(50) | | |
upwd | character varying(40) | | |
uid | integer | | not null | nextval('test4_uid_seq'::regclass)
uxdb=# select * from test4;
uname | upwd | uid
-------+------+-----
song1 | 123 | 1
song2 | 456 | 2
(2 rows)
uxdb=# insert into test4 values ('song3','666',1);
INSERT 0 1
uxdb=# select * from test4;
uname | upwd | uid
-------+------+-----
song1 | 123 | 1
song2 | 456 | 2
song3 | 666 | 1
(3 rows)
uxdb=#
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16408;
contype | conname | conrelid | conindid
---------+---------+----------+----------
(0 rows)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16408;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select oid from ux_class where relname='test4';
oid
-------
16408
(1 row)
uxdb=#
--删除主键约束之后，表结构就没有什么索引和约束了
外键约束
| 外键约束 |
外键约束主要是用来维护子表（引用表）和父表（被引用表）之间的引用完整性。
1、使用列约束设置外键
uxdb=# create table test(uid int,uname varchar(50),upwd varchar(40),primary key(uid));
CREATE TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | not null |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_pkey" PRIMARY KEY, btree (uid)
--说明：外键默认名称为tablename_columnname_fkey
uxdb=# create table test_info(uid int primary key references test,uname varchar(50),upwd varchar(40));
CREATE TABLE
uxdb=# \d test_
test_info test_info_pkey test_pkey
uxdb=# \d test_info_pkey
Index "public.test_info_pkey"
Column | Type | Definition
--------+---------+------------
uid | integer | uid
primary key, btree, for table "public.test_info"
uxdb=# \d test_info
Table "public.test_info"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | not null |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_info_pkey" PRIMARY KEY, btree (uid)
Foreign-key constraints:
"test_info_uid_fkey" FOREIGN KEY (uid) REFERENCES test(uid)
uxdb=# \d test_pkey
Index "public.test_pkey"
Column | Type | Definition
--------+---------+------------
uid | integer | uid
primary key, btree, for table "public.test"
uxdb=#
下面先看一下父表的结构：
uxdb=# select * from ux_tables where tablename = 'test';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test | uxdb | | t | f | t | f
(1 row)
uxdb=# select oid from ux_class where relname='test';
oid
-------
16384
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16384;
contype | conname | conrelid | conindid
---------+-----------+----------+----------
p | test_pkey | 16384 | 16387
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16384;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16387 | 1 | t | t | t | t
(1 row)
再看一下子表的结构：
uxdb=# select * from ux_tables where tablename = 'test_info';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test_info | uxdb | | t | f | t | f
(1 row)
uxdb=# select oid from ux_class where relname='test_info';
oid
-------
16389
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16389;
contype | conname | conrelid | conindid
---------+--------------------+----------+----------
p | test_info_pkey | 16389 | 16392
f | test_info_uid_fkey | 16389 | 16387
(2 rows)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16389;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16392 | 1 | t | t | t | t
(1 row)
uxdb=#
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16389;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
------------------------------+--------+--------+-----------+--------------+---------------+---------------+--------------
RI_ConstraintTrigger_c_16397 | 1644 | 5 | O | t | 16384 | 16387 | 16394
RI_ConstraintTrigger_c_16398 | 1645 | 17 | O | t | 16384 | 16387 | 16394
(2 rows)
2、使用表约束设置外键
--说明：外键默认名称为tablename_columnname_fkey
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | not null |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_pkey" PRIMARY KEY, btree (uid)
uxdb=# create table test_info(uid int,uname varchar(50),upwd varchar(40),foreign key(uid) references test);
CREATE TABLE
uxdb=# \d test_info
Table "public.test_info"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Foreign-key constraints:
"test_info_uid_fkey" FOREIGN KEY (uid) REFERENCES test(uid)
uxdb=#
此时的子表只有一个外键（关联父表的主键）（没有什么索引），其结构如下：
uxdb=# select oid from ux_class where relname='test_info';
oid
-------
16399
(1 row)
uxdb=# select * from ux_tables where tablename = 'test_info';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test_info | uxdb | | f | f | t | f
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16399;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16399;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
------------------------------+--------+--------+-----------+--------------+---------------+---------------+--------------
RI_ConstraintTrigger_c_16405 | 1644 | 5 | O | t | 16384 | 16387 | 16402
RI_ConstraintTrigger_c_16406 | 1645 | 17 | O | t | 16384 | 16387 | 16402
(2 rows)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16399;
contype | conname | conrelid | conindid
---------+--------------------+----------+----------
f | test_info_uid_fkey | 16399 | 16387
(1 row)
uxdb=# O o 0
注：我们可以看到对一个表创建外键约束时，其内部实现是对外键相关的两个表创建触发器（为外键创建的 ），然后在更新表时触发触发器去进行外键的检测。
触发器系统表里面的oid=16384 是指test表：
uxdb=# select oid from ux_class where relname='test';
oid
-------
16384
(1 row)
而子表里面是没有支持什么索引的，但是在触发器系统表里面出现的字段tgconstrindid =16387是指的是父表的主键索引;
uxdb=# select oid from ux_class where relname='test';
oid
-------
16384
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16384;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16387 | 1 | t | t | t | t
(1 row)
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | not null |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_pkey" PRIMARY KEY, btree (uid)
Referenced by:
TABLE "test_info" CONSTRAINT "test_info_uid_fkey" FOREIGN KEY (uid) REFERENCES test(uid)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16384;
contype | conname | conrelid | conindid
---------+-----------+----------+----------
p | test_pkey | 16384 | 16387
(1 row)
uxdb=#
3、通过修改表结构设置外键
--语法：alter table table_name add [constraint constraint_name] foreign key(column_1) references TableName(ColumnName);
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | not null |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_pkey" PRIMARY KEY, btree (uid)
uxdb=# create table test_info(uid int,uname varchar(50),upwd varchar(40));
CREATE TABLE
uxdb=# \d test_info
Table "public.test_info"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
uxdb=# select oid from ux_class where relname='test_info';
oid
-------
16407
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16407;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16407;
contype | conname | conrelid | conindid
---------+---------+----------+----------
(0 rows)
--说明：通过修改表结构设置外键，可以指定外键名称。
uxdb=# alter table test_info add constraint myfkey foreign key(uid) references test;
ALTER TABLE
uxdb=# \d test_info
Table "public.test_info"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Foreign-key constraints:
"myfkey" FOREIGN KEY (uid) REFERENCES test(uid)
uxdb=#
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16407;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16407;
contype | conname | conrelid | conindid
---------+---------+----------+----------
f | myfkey | 16407 | 16387
(1 row)
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16407;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
------------------------------+--------+--------+-----------+--------------+---------------+---------------+--------------
RI_ConstraintTrigger_c_16418 | 1644 | 5 | O | t | 16384 | 16387 | 16415
RI_ConstraintTrigger_c_16419 | 1645 | 17 | O | t | 16384 | 16387 | 16415
(2 rows)
uxdb=#
--这个和上面大同小异
4、删除外键约束（同删除其他约束一样，使用同一语法
uxdb=# \d test_info
Table "public.test_info"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Foreign-key constraints:
"myfkey" FOREIGN KEY (uid) REFERENCES test(uid)
uxdb=# alter table test_info drop constraint myfkey ;
ALTER TABLE
uxdb=# \d test_info
Table "public.test_info"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16407;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
--------+--------+--------+-----------+--------------+---------------+---------------+--------------
(0 rows)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16407;
contype | conname | conrelid | conindid
---------+---------+----------+----------
(0 rows)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16407;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=#
唯一约束
这个可以参见主键约束！（有相似之处，但是也有些许区别）
所谓唯一约束：确保[列]或[列组]中的值在表中是唯一的。
| 唯一约束 |
1、使用列约束设置唯一约束
--生成2个列的唯一约束test_uid_key
uxdb=# create table test(uid int unique ,uname varchar(50),upwd varchar(40));
CREATE TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_uid_key" UNIQUE CONSTRAINT, btree (uid)
uxdb=#
看看系统表结构显示：
uxdb=# create table test(uid int unique ,uname varchar(50),upwd varchar(40));
CREATE TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_uid_key" UNIQUE CONSTRAINT, btree (uid)
uxdb=# select oid from ux_class where relname='test';
oid
-------
16420
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16420;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
16423 | 1 | t | f | t | t
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16420;
contype | conname | conrelid | conindid
---------+--------------+----------+----------
u | test_uid_key | 16420 | 16423
(1 row)
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16420;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
--------+--------+--------+-----------+--------------+---------------+---------------+--------------
(0 rows)
uxdb=# select * from ux_tables where tablename = 'test';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test | uxdb | | t | f | f | f
(1 row)
uxdb=#
--只有一个index（唯一性索引）
2、使用表级约束设置唯一约束
3、通过修改表结构设置唯一约束
道理差不多，就不写了
4、删除约束
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
Indexes:
"test_uid_key" UNIQUE CONSTRAINT, btree (uid)
uxdb=# alter table test drop constraint test_uid_key;
ALTER TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+-----------------------+-----------+----------+---------
uid | integer | | |
uname | character varying(50) | | |
upwd | character varying(40) | | |
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16420;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16420;
contype | conname | conrelid | conindid
---------+---------+----------+----------
(0 rows)
uxdb=#
检查约束
所谓检查约束：基于布尔表达式约束表中列的值。
| 检查约束 |
1、使用列约束设置检查约束
uxdb=# create table test(uid int check(uid>0));
CREATE TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
uid | integer | | |
Check constraints:
"test_uid_check" CHECK (uid > 0)
uxdb=# select * from ux_tables where tablename = 'test';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test | uxdb | | f | f | f | f
(1 row)
uxdb=# select oid from ux_class where relname='test';
oid
-------
16425
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16425;
contype | conname | conrelid | conindid
---------+----------------+----------+----------
c | test_uid_check | 16425 | 0
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16425;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16425;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
--------+--------+--------+-----------+--------------+---------------+---------------+--------------
(0 rows)
uxdb=#
2、使用表约束设置检查约束
3、通过修改表结构设置检查约束
uxdb=# create table test(uid int);
CREATE TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
uid | integer | | |
uxdb=# select * from ux_tables where tablename = 'test';
schemaname | tablename | tableowner | tablespace | hasindexes | hasrules | hastriggers | rowsecurity
------------+-----------+------------+------------+------------+----------+-------------+-------------
public | test | uxdb | | f | f | f | f
(1 row)
uxdb=# select oid from ux_class where relname='test';
oid
-------
16429
(1 row)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16429;
contype | conname | conrelid | conindid
---------+---------+----------+----------
(0 rows)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16429;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16429;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
--------+--------+--------+-----------+--------------+---------------+---------------+--------------
(0 rows)
uxdb=# alter table test add constraint mycheck check(uid>0);
ALTER TABLE
uxdb=# \d test
Table "public.test"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+---------
uid | integer | | |
Check constraints:
"mycheck" CHECK (uid > 0)
uxdb=# select contype,conname,conrelid,conindid from ux_constraint where conrelid=16429;
contype | conname | conrelid | conindid
---------+---------+----------+----------
c | mycheck | 16429 | 0
(1 row)
uxdb=# select indexrelid,indnatts,indisunique,indisprimary,indisvalid,indislive from ux_index where indrelid=16429;
indexrelid | indnatts | indisunique | indisprimary | indisvalid | indislive
------------+----------+-------------+--------------+------------+-----------
(0 rows)
uxdb=# select tgname,tgfoid,tgtype,tgenabled,tgisinternal,tgconstrrelid,tgconstrindid,tgconstraint from ux_trigger where tgrelid=16429;
tgname | tgfoid | tgtype | tgenabled | tgisinternal | tgconstrrelid | tgconstrindid | tgconstraint
--------+--------+--------+-----------+--------------+---------------+---------------+--------------
(0 rows)
uxdb=#