34 lines
1.4 KiB
Markdown
34 lines
1.4 KiB
Markdown
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# Considerations before upgrading Friendica
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* [Home](help)
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## MySQL >= 5.7.4
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Starting from MySQL version 5.7.4, the IGNORE keyword in ALTER TABLE statements is ignored.
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This prevents automatic table deduplication if a UNIQUE index is added to a Friendica table's structure.
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If a DB update fails for you while creating a UNIQUE index, make sure to manually deduplicate the table before trying the update again.
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### Manual deduplication
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There are two main ways of doing it, either by manually removing the duplicates or by recreating the table.
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Manually removing the duplicates is usually faster if they're not too numerous.
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To manually remove the duplicates, you need to know the UNIQUE index columns available in `database.sql`.
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```SQL
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SELECT GROUP_CONCAT(id), <index columns>, count(*) as count FROM users
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GROUP BY <index columns> HAVING count >= 2;
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/* delete or merge duplicate from above query */;
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```
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If there are too many rows to handle manually, you can create a new table with the same structure as the table with duplicates and insert the existing content with INSERT IGNORE.
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To recreate the table you need to know the table structure available in `database.sql`.
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```SQL
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CREATE TABLE <table_name>_new <rest of the CREATE TABLE>;
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INSERT IGNORE INTO <table_name>_new SELECT * FROM <table_name>;
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DROP TABLE <table_name>;
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RENAME TABLE <table_name>_new TO <table_name>;
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```
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This method is slower overall, but it is better suited for large numbers of duplicates.
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