Question

Assume these two tables:

blog

id title      keywords
1  Hello      hello,world,test
2  Google     search, email, security
3  Microsoft  clippy, collaboration

category

id keywords
1  test, world, clippy

How do I search for blog rows that have one or more keyword matching a keyword in the category row?

Answer 1

Succinctly: if you want to do that operation, you don’t store your data like that. You normalize your data, and search using the normalized data:

CREATE TABLE Blog
(
    id      INTEGER NOT NULL PRIMARY KEY,
    title   VARCHAR(30) NOT NULL
);

INSERT INTO Blog(id, title) VALUES(1, 'Hello');
INSERT INTO Blog(id, title) VALUES(2, 'Google');
INSERT INTO Blog(id, title) VALUES(3, 'Microsoft');

CREATE TABLE BlogKeywords
(
    id      INTEGER NOT NULL,
    keyword VARCHAR(20) NOT NULL,
    PRIMARY KEY(keyword, id)
);

INSERT INTO BlogKeywords(id, keyword) VALUES(1, 'hello');
INSERT INTO BlogKeywords(id, keyword) VALUES(1, 'world');
INSERT INTO BlogKeywords(id, keyword) VALUES(1, 'test');
INSERT INTO BlogKeywords(id, keyword) VALUES(2, 'search');
INSERT INTO BlogKeywords(id, keyword) VALUES(2, 'email');
INSERT INTO BlogKeywords(id, keyword) VALUES(2, 'security');
INSERT INTO BlogKeywords(id, keyword) VALUES(3, 'clippy');
INSERT INTO BlogKeywords(id, keyword) VALUES(3, 'collaboration');

CREATE TABLE Category
(
    id      INTEGER NOT NULL,
    keyword VARCHAR(20) NOT NULL,
    PRIMARY KEY(id, keyword)
);

INSERT INTO Category(id, keyword) VALUES(1, 'test');
INSERT INTO Category(id, keyword) VALUES(1, 'world');
INSERT INTO Category(id, keyword) VALUES(1, 'clippy');

Now you can search easily using simple joins:

SELECT DISTINCT b.id AS BlogID, b.Title, c.id AS CategoryID
  FROM Blog AS b
  JOIN BlogKeywords AS K ON b.id      = k.id
  JOIN Category     AS C ON k.keyword = c.keyword;

It isn’t completely clear what you’d want to see if there were multiple catagories.