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问题描述
我无法理解创建组合键时的语法错误。
I cannot understand the syntax error in creating a composite key. It may be a logic error, because I have tested many varieties.
如何在Postgres中创建复合键？
CREATE TABLE tags
(
(question_id, tag_id) NOT NULL,
question_id INTEGER NOT NULL,
tag_id SERIAL NOT NULL,
tag1 VARCHAR(20),
tag2 VARCHAR(20),
tag3 VARCHAR(20),
PRIMARY KEY(question_id, tag_id),
CONSTRAINT no_duplicate_tag UNIQUE (question_id, tag_id)
);
ERROR: syntax error at or near "("
LINE 3: (question_id, tag_id) NOT NULL,
^
推荐答案
您的化合物 PRIMARY KEY 规范已经满足您的要求。这也会给您带来语法错误，并省略多余的 CONSTRAINT （已经暗示）：
Your compound PRIMARY KEY specification already does what you want. Omit the line that's giving you a syntax error, and omit the redundant CONSTRAINT (already implied), too:
CREATE TABLE tags
(
question_id INTEGER NOT NULL,
tag_id SERIAL NOT NULL,
tag1 VARCHAR(20),
tag2 VARCHAR(20),
tag3 VARCHAR(20),
PRIMARY KEY(question_id, tag_id)
);
NOTICE: CREATE TABLE will create implicit sequence "tags_tag_id_seq" for serial column "tags.tag_id"
NOTICE: CREATE TABLE / PRIMARY KEY will create implicit index "tags_pkey" for table "tags"
CREATE TABLE
pg=> \d tags
Table "public.tags"
Column | Type | Modifiers
-------------+-----------------------+-------------------------------------------------------
question_id | integer | not null
tag_id | integer | not null default nextval('tags_tag_id_seq'::regclass)
tag1 | character varying(20) |
tag2 | character varying(20) |
tag3 | character varying(20) |
Indexes:
"tags_pkey" PRIMARY KEY, btree (question_id, tag_id)
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