MySQL Replace and on DUPLICATE KEY update use

REPLACE

We may encounter this situation frequently when working with databases. If a table has a unique index on a field, when we insert a record into the table with a key value that already exists, it will throw a primary key conflict error. Of course, we might want to overwrite the original record value with the value of the new record. If you use the traditional approach, you must first delete the original record by using the DELETE statement, and then insert the new record using insert. And in MySQL we provide a new solution, which is the replace statement. When inserting a record with replace, replace is the same as the Insert function, and replace replaces the original record value with the value of the new record if it is duplicated.

The biggest benefit of using replace is that you can combine delete and insert to form an atomic operation. This eliminates the need to consider complex operations such as adding transactions while using delete and insert.

When using replace, the table must have a unique index, and the field in which the index resides cannot allow null values, otherwise the replace is exactly the same as the insert.

After you perform the replace, the system returns the number of rows affected, and if 1 is returned, indicating that there are no duplicate records in the table, and if 2 is returned, a duplicate record is called, and the system automatically calls the delete to delete the record, and then records inserts to insert the record. If the value returned is greater than 2, it indicates that there are multiple unique indexes, and that multiple records are deleted and inserted.

INSERT ... On DUPLICATE KEY UPDATE

INSERT ... On DUPLICATE KEY Update: When inserting data, if the value of the corresponding primary key or unique index in the inserted data already exists in the table, the field value corresponding to this data is modified. If it does not exist, insert it directly.

If you specify an on DUPLICATE KEY update and the insert row causes duplicate values to appear in a unique index or primary KEY, the old line UPDATE is performed. For example, if column A is defined as unique and contains a value of 1, the following two statements have the same effect:

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1. Mysql>INSERT into table (a,b,c) VALUES
2. -OnDUPLICATE KEY UPDATE c=c+1;
3. mysql>UPDATE table SET c=c+1 WHERE a=1;

If the row is inserted as a new record, the value of the affected row is 1, and if the original record is updated, the value of the affected row is 2.
NOTE: If column B is also a unique column, insert is equivalent to this UPDATE statement

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1. mysql>UPDATE table SET c=c+1 WHERE a=1 OR b=2 LIMIT 1;

If A=1 OR b=2 matches multiple rows, only one row is updated. In general, you should try to avoid using the on DUPLICATE key clause on tables with multiple unique keywords.
You can use the values (col_name) function from the Insert ... in the UPDATE clause. The insert portion of the UPDATE statement refers to the column value. In other words, if a duplicate keyword conflict does not occur, values (col_name) in the update clause can refer to the value of the col_name being inserted. This function is especially useful for multi-row insertions. The VALUES () function is only in the insert ... The UPDATE statement makes sense, and returns null at other times.
When you use the on DUPLICATE KEY update, the delayed option is ignored.

The SQL statement for the above question is:

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1. INSERT INTO st_movie (Id,orderby) values (9,3), (3,4), (4,5), (5,6), (6,7), (7,8), (8,9) on DUPLICATE KEY  UPDATE ' by ' = values (' by ') ';

MySQL Replace and on DUPLICATE KEY update use