SQL enforce value of a column if other column is NOT NULL
I'm having a hard time to explain this so let me illustrate it with an exemple.
I have a table for comments and it looks like so:
CREATE TABLE comments (
id INT UNSIGNED AUTO_INCREMENT,
parent_id INT UNSIGNED,
article_id INT UNSIGNED NOT NULL,
user_id INT UNSIGNED NOT NULL,
ip VARCHAR(255) NOT NULL,
submitted_at TIMESTAMP DEFAULT NOW(),
comment TEXT,
PRIMARY KEY (id),
CONSTRAINT fk_com_parent
FOREIGN KEY (parent_id)
REFERENCES comments (id)
CONSTRAINT fk_com_article
FOREIGN KEY (article_id)
REFERENCES articles (id)
CONSTRAINT fk_com_user
FOREIGN KEY (user_id)
REFERENCES users (id)
);
Now it makes sense that if parent_id is set, child and parent should share the same article_id.
Answers to a comment must be on the same article. So is there a way to contraint this?
mysql foreign-key
asked 11 mins ago
BuzutBuzut
228138
add a comment |
I'm having a hard time to explain this so let me illustrate it with an exemple.
I have a table for comments and it looks like so:
CREATE TABLE comments (
id INT UNSIGNED AUTO_INCREMENT,
parent_id INT UNSIGNED,
article_id INT UNSIGNED NOT NULL,
user_id INT UNSIGNED NOT NULL,
ip VARCHAR(255) NOT NULL,
submitted_at TIMESTAMP DEFAULT NOW(),
comment TEXT,
PRIMARY KEY (id),
CONSTRAINT fk_com_parent
FOREIGN KEY (parent_id)
REFERENCES comments (id)
CONSTRAINT fk_com_article
FOREIGN KEY (article_id)
REFERENCES articles (id)
CONSTRAINT fk_com_user
FOREIGN KEY (user_id)
REFERENCES users (id)
);
Now it makes sense that if parent_id is set, child and parent should share the same article_id.
Answers to a comment must be on the same article. So is there a way to contraint this?
mysql foreign-key
asked 11 mins ago
BuzutBuzut
228138
probably could be done with triggers. Is it necessary to duplicate. recursive CTEs (MySQL-8.0/MariaDB-10.2) mean these are derivable in a query.
– danblack
2 mins ago
add a comment |
I'm having a hard time to explain this so let me illustrate it with an exemple.
I have a table for comments and it looks like so:
CREATE TABLE comments (
id INT UNSIGNED AUTO_INCREMENT,
parent_id INT UNSIGNED,
article_id INT UNSIGNED NOT NULL,
user_id INT UNSIGNED NOT NULL,
ip VARCHAR(255) NOT NULL,
submitted_at TIMESTAMP DEFAULT NOW(),
comment TEXT,
PRIMARY KEY (id),
CONSTRAINT fk_com_parent
FOREIGN KEY (parent_id)
REFERENCES comments (id)
CONSTRAINT fk_com_article
FOREIGN KEY (article_id)
REFERENCES articles (id)
CONSTRAINT fk_com_user
FOREIGN KEY (user_id)
REFERENCES users (id)
);
Now it makes sense that if parent_id is set, child and parent should share the same article_id.
Answers to a comment must be on the same article. So is there a way to contraint this?
mysql foreign-key
asked 11 mins ago
BuzutBuzut
228138
I'm having a hard time to explain this so let me illustrate it with an exemple.
I have a table for comments and it looks like so:
CREATE TABLE comments (
id INT UNSIGNED AUTO_INCREMENT,
parent_id INT UNSIGNED,
article_id INT UNSIGNED NOT NULL,
user_id INT UNSIGNED NOT NULL,
ip VARCHAR(255) NOT NULL,
submitted_at TIMESTAMP DEFAULT NOW(),
comment TEXT,
PRIMARY KEY (id),
CONSTRAINT fk_com_parent
FOREIGN KEY (parent_id)
REFERENCES comments (id)
CONSTRAINT fk_com_article
FOREIGN KEY (article_id)
REFERENCES articles (id)
CONSTRAINT fk_com_user
FOREIGN KEY (user_id)
REFERENCES users (id)
);
Now it makes sense that if parent_id is set, child and parent should share the same article_id.
Answers to a comment must be on the same article. So is there a way to contraint this?
mysql foreign-key
mysql foreign-key
asked 11 mins ago
BuzutBuzut
228138
asked 11 mins ago
BuzutBuzut
228138
asked 11 mins ago
BuzutBuzut
228138
asked 11 mins ago
BuzutBuzut
228138
asked 11 mins ago
BuzutBuzut
228138
228138
probably could be done with triggers. Is it necessary to duplicate. recursive CTEs (MySQL-8.0/MariaDB-10.2) mean these are derivable in a query.
– danblack
2 mins ago
add a comment |
probably could be done with triggers. Is it necessary to duplicate. recursive CTEs (MySQL-8.0/MariaDB-10.2) mean these are derivable in a query.
– danblack
2 mins ago
probably could be done with triggers. Is it necessary to duplicate. recursive CTEs (MySQL-8.0/MariaDB-10.2) mean these are derivable in a query.
– danblack
2 mins ago
probably could be done with triggers. Is it necessary to duplicate. recursive CTEs (MySQL-8.0/MariaDB-10.2) mean these are derivable in a query.
– danblack
2 mins ago
add a comment |
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probably could be done with triggers. Is it necessary to duplicate. recursive CTEs (MySQL-8.0/MariaDB-10.2) mean these are derivable in a query.
– danblack
2 mins ago