Postgresql Postgres将唯一索引添加到已在分区上具有PK的分区表中，然后添加PK

当向表分区上已有该PK的分区表添加唯一索引，然后添加PK时，PK创建失败，错误为multiple primary keys for table X are not allowed

为什么会出现这种限制和奇怪的错误消息？不是应该管用吗？

场景1:索引然后主键-失败

CREATE TABLE tst_t (
    c1 int4 NOT NULL,
    c2 int8 NOT NULL,
    c3 int8 NOT NULL
)
PARTITION BY LIST (c1);

CREATE TABLE tst_t_988 PARTITION OF tst_t (
    CONSTRAINT pk_tst_t_988 PRIMARY KEY (c1)
) FOR VALUES IN (988);

create unique index pk_tst_t on tst_t using btree (c1);

alter table tst_t add primary key (c1);

-- SQL Error [42P16]: ERROR: multiple primary keys for table "tst_t_988" are not allowed

场景2:没有索引则PK-Works

drop table tst_t;

CREATE TABLE tst_t (
    c1 int4 NOT NULL,
    c2 int8 NOT NULL,
    c3 int8 NOT NULL
)
PARTITION BY LIST (c1);

CREATE TABLE tst_t_988 PARTITION OF tst_t (
    CONSTRAINT pk_tst_t_988 PRIMARY KEY (c1)
) FOR VALUES IN (988);

-- this time not creating the index
--create unique index pk_tst_t on tst_t using btree (c1);

alter table tst_t add primary key (c1);

-- works

场景3:只对已分区的表进行索引，然后使用PK-Works

drop table tst_t;

CREATE TABLE tst_t (
    c1 int4 NOT NULL,
    c2 int8 NOT NULL,
    c3 int8 NOT NULL
)
PARTITION BY LIST (c1);

CREATE TABLE tst_t_988 PARTITION OF tst_t (
    CONSTRAINT pk_tst_t_988 PRIMARY KEY (c1)
) FOR VALUES IN (988);

-- this time index on ONLY partitioned table
create unique index pk_tst_t on only tst_t using btree (c1);

alter table tst_t add primary key (c1);

-- works