How to delete duplicate rows in MySQL table
In database management, eliminating duplicate data is a common task. In MySQL, this can be achieved using the DELETE command.
The following is a sample table:
CREATE TABLE names ( id INT NOT NULL AUTO_INCREMENT, name VARCHAR(255) NOT NULL, PRIMARY KEY (id) );
Suppose the table contains duplicates:
INSERT INTO names (name) VALUES ('google'); INSERT INTO names (name) VALUES ('yahoo'); INSERT INTO names (name) VALUES ('msn'); INSERT INTO names (name) VALUES ('google'); INSERT INTO names (name) VALUES ('google'); INSERT INTO names (name) VALUES ('yahoo'); SELECT * FROM names;
To remove all duplicate rows (keep the row with the smallest ID), use the following query:
DELETE n1 FROM names n1, names n2 WHERE n1.id > n2.id AND n1.name = n2.name;
Alternatively, to keep the row with the largest ID, use the following query:
DELETE n1 FROM names n1, names n2 WHERE n1.id < n2.id AND n1.name = n2.name;
Warning: Be sure to back up your tables before executing any delete queries to avoid accidental data loss.
For large tables, it is recommended to use the faster INSERT and DISTINCT methods:
```sql CREATE TEMPORARY TABLE temp_names SELECT DISTINCT id, name FROM names; TRUNCATE TABLE names; INSERT INTO names (id, name) SELECT id, name FROM temp_names; DROP TABLE temp_names; ```The above is the detailed content of How to Efficiently Delete Duplicate Rows in a MySQL Table?. For more information, please follow other related articles on the PHP Chinese website!

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