#Mysql add column statene how to#
#Mysql add column statene update#

Incrementing the buffer speeds up the index creation. When an index is created, the storage engine may use a configurable buffer in the process. This statement can also be used to rename a table. Also, note that IGNORE is accepted but ignored in ALTER TABLE. This can be useful if a column (or a set of columns) should be UNIQUE but it contains duplicate values however, this technique provides no control on which rows are preserved and which are deleted. To suppress the error and force the creation of UNIQUE indexes, discarding duplicates, the IGNORE option can be specified. When adding a UNIQUE index on a column (or a set of columns) which have duplicated values, an error will be produced and the statement will be stopped. This is also true for non-transactional tables. If another connection is using the table, a metadata lock is active, and this statement will wait until the lock is released.

You can also change the comment for the table and the storage engine of the | EXCHANGE PARTITION partition_name WITH TABLE tbl_nameĪLTER TABLE enables you to change the structure of an existing table.įor example, you can add or delete columns, create or destroy indexes,Ĭhange the type of existing columns, or rename columns or the table | partition_options | CONVERT TABLE normal_table TO partition_definition | CONVERT PARTITION partition_name TO TABLE tbl_name

#Mysql add column statene update#

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.ALTER TABLE tbl_nameĪlter_specification.

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:

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. Using INSERT IGNORE effectively causes MySQL to ignore execution errors while attempting to perform INSERT statements.

#Mysql add column statene how to#

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.