unique-constraint

How do I specify unique constraint for multiple columns in MySQL?

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To add a unique constraint, you need to use two components: ALTER TABLE – to change the table schema and, ADD UNIQUE – to add the unique constraint. You then can define your new unique key with the format ‘name'(‘column1’, ‘column2’…) So for your particular issue, you could use this command: ALTER TABLE `votes` ADD … Read more

How can I do ‘insert if not exists’ in MySQL?

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Use INSERT IGNORE INTO table. There’s also INSERT … ON DUPLICATE KEY UPDATE syntax, and you can find explanations in 13.2.6.2 INSERT … ON DUPLICATE KEY UPDATE Statement. Post from bogdan.org.ua according to Google’s webcache: 18th October 2007 To start: as of the latest MySQL, syntax presented in the title is not possible. But there … Read more