![]() ![]() In summary, REPLACE INTO may be right for your implementation, but you might find it more appropriate (and less risky) to use INSERT. ON DPLICATE KEY resulted in a ten fold more throughput (measured in queries per second) and a drastic decrease in IO operations and in load average. On a production system I've seen, changing REPLACE INTO to INSERT INTO. Many uses of REPLACE INTO have no intention of changing PRIMARY KEY (or other UNIQUE KEY) values. To change the data type of a column in a table, use the following syntax: ALTER TABLE tablename MODIFY COLUMN columnname datatype MySQL ALTER TABLE Example Look at the 'Persons' table: Now we want to add a column named 'DateOfBirth' in the 'Persons' table. The problem is, if there's a PRIMARY KEY on that table, and the REPLACE INTO does not specify a value for the PRIMARY KEY (for example, it's an AUTO_INCREMENT column), the new row gets a different value, and this may not be what you were looking for in terms of behavior. 18.1k 34 95 118 Add a comment 2 Answers Sorted by: 24 Try this one mysql'select replace (text,'\'',\''\') from mytable' Then the query will become select replace (text,''',''') from mytable at the Mysql end. The row doesn't just get updated, it is completely removed. ON DUPLICATE KEYĪlso, there's the notion of "well, if the row isn't there, we create it. After many REPLACE INTO executions, it is most probable that your index is more fragmented than it would have been, had you used SELECT/UPDATE or INSERT INTO. Nodes may need to be split due to INSERT. Index nodes may need to be merged upon DELETE. The restructuring of an index is an expensive operation. Especially on InnoDB tables (because of their clustered nature), this means much overhead. When a new row is inserted, the same happens. Whenever a row is deleted, all indexes need to be updated, and most importantly the PRIMARY KEY. It may be just what you were looking for in terms of ease of use, but the fact is that on duplicate keys, a DELETE and INSERT are performed, and this calls for a closer look. Shlomi Noach writes about the problem with using REPLACE INTO here:īut weak hearted people as myself should be aware of the following: it is a heavyweight solution. ![]() ON DUPLICATE KEY UPDATE is non-destructive, in that it will only ever issue INSERT or UPDATE statements, but never DELETE.įor example, we have decided we wish to replace our id = 1 record of Green Eggs and Ham and revert it back to the original In Search of Lost Time record instead.REPLACE does work much like an INSERT that just overwrites records that have the same PRIMARY KEY or UNIQUE index, however, beware. ![]() Unlike REPLACE – an inherently destructive command due to the DELETE commands it performs when necessary – using INSERT. ON DUPLICATE KEY UPDATE statement and clause. The alternative (and generally preferred) method for INSERTING into rows that may contain duplicate UNIQUE or PRIMARY KEY values is to use the INSERT. More information on using REPLACE can be found in the official documentation. Notice that even though we only altered one row, the result indicates that two rows were affected because we actually DELETED the existing row then INSERTED the new row to replace it. Seuss', 1960 ) Query OK, 2 rows affected ( 0. Mysql > REPLACE INTO books ( id, title, author, year_published ) VALUES ( 1, 'Green Eggs and Ham', 'Dr. The obvious purpose is to execute a large number of INSERT statements for a combination of data that is both already existing in the database as well as new data coming into the system.įor example, our books table might contain a few records already: Instead we know that all the ASCII characters that doesn't involves special character lies within ASCII codes \x20-\x7E (Hex representation). This means that an INSERT IGNORE statement which contains a duplicate value in a UNIQUE index or PRIMARY KEY field does not produce an error, but will instead simply ignore that particular INSERT command entirely. This solution doesn't involves creating procedures or functions or lengthy use of replace within replace. CREATE OR REPLACE VIEW Syntax CREATE OR REPLACE VIEW viewname AS SELECT column1, column2. Using INSERT IGNORE effectively causes MySQL to ignore execution errors while attempting to perform INSERT statements. A view can be updated with the CREATE OR REPLACE VIEW statement. MySQL provides a number of useful statements when it is necessary to INSERT rows after determining whether that row is, in fact, new or already exists.īelow we’ll examine the three different methods and explain the pros and cons of each in turn so you have a firm grasp on how to configure your own statements when providing new or potentially existing data for INSERTION. ![]()
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