An UPDATE SQL statement modifies existing rows in a table by setting new values for one or more columns that satisfy an optional WHERE filter.
An UPDATE statement changes data in-place, letting you set new column values for rows that match a WHERE clause; without WHERE it touches every row.
Use UPDATE to correct errors, apply business-rule changes, or sync data after imports when you need to keep primary keys intact instead of inserting new rows.
The engine finds candidate rows, creates new row versions with your SET values, marks old versions for cleanup, and writes to the transaction log for rollback support.
Always start with a selective WHERE; alias the table and test with SELECT first to avoid unintended bulk updates.
Provide one or many comma-separated column = expression pairs after SET; expressions can reference other columns or sub-queries.
Yes—separate each column assignment with a comma: UPDATE users SET last_login = NOW(), status = 'active' WHERE id = 42;.
Use a JOIN or sub-query: UPDATE t1 SET price = t2.price FROM t1 JOIN t2 ON t1.id = t2.id;—supported in PostgreSQL, SQL Server, MySQL 8 +.
Wrap in a transaction, back up affected data, add LIMIT/TOP during testing, and log row counts; use CASCADE rules cautiously.
Galaxy’s AI copilot autocompletes table names, warns about missing WHERE clauses, and previews the row count, reducing risky bulk updates.
Accurate data is the backbone of analytics. UPDATE lets engineers correct, enrich, and de-duplicate data without breaking foreign-key relationships or re-loading full tables. Mastering UPDATE ensures cleaner data pipelines, faster incident response, and safer schema evolution—critical skills for data engineers who own production warehouses.
Start a transaction before running UPDATE. If the result looks wrong, issue ROLLBACK. Without a transaction, restore from backups or WAL logs.
Yes. Use a writable CTE: WITH upd AS (UPDATE t SET x = 1 WHERE y = 2 RETURNING *) SELECT * FROM upd; to view changed rows.
No. UPDATE only changes specified columns; others keep their existing values unless explicitly set to DEFAULT.
Galaxy’s editor flags statements lacking WHERE, shows estimated row counts, and suggests adding a transaction, preventing unintended mass updates.
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