try

mysql --force < sample_data.sql

Mysql help section says

 -f, --force         Continue even if we get an sql error.

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You could also use INSERT IGNORE

INSERT IGNORE INTO mytable

 (primaryKey, field1, field2)

VALUES

 ('1', 1, 2),

 ('1', 3, 4), //will not be inserted

 ('2', 5, 6); //will be inserted

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You can use INSERT... IGNORE syntax if you want to take no action when there's a duplicate record.

You can use REPLACE INTO syntax if you want to overwrite an old record with a new one with the same key.

Or, you can use INSERT... ON DUPLICATE KEY UPDATE syntax if you want to perform an update to the record instead when you encounter a duplicate.

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REF: