![]() For more information, see Section 13.1.20, CREATE TABLE Statement. On MySQL 5.7, I didnt find a way to use CURRENTDATE or its synonyms as default. ![]() ![]() columndefinition clauses use the same syntax for ADD and CHANGE as for CREATE TABLE. But, the question is how we can do this using SQL commands? Well let's find out. The syntax for many of the permissible alterations is similar to clauses of the CREATE TABLE statement. Now suppose that we want to expand the existing shippers table by adding one more column. We'll use this shippers table for all of our ALTER TABLE statements. | shipper_name | varchar(60) | NO | | NULL | | You assign some constraints to limit the type of data that can go into a table. | shipper_id | int | NO | PRI | NULL | auto_increment | Now, to add a column with a default value to an existing table, we can use them together as below. | Field | Type | Null | Key | Default | Extra | To set a default value, we use the DEFAULT constraint. alter table oldorders add constraint uniqueorders UNIQUE (orderid,amount) Ubiq makes it easy to visualize data in minutes, and monitor in real-time dashboards. ![]() In such situation you can use the ALTER TABLE statement to alter or change an existing table by adding, changing, or deleting a column in the table.Ĭonsider we've a shippers table in our database, whose structure is as follows: You can also add UNIQUE CONSTRAINT to multiple columns using ALTER TABLE statement. It is quite possible that after creating a table, as you start using it, you may discover you've forgot to mention any column or constraint or specified a wrong name for the column. MySQL compatibility It is not supported to add a CHECK constraint while adding a column (for example, ALTER TABLE t ADD COLUMN a CHECK(a > 0) ). In this tutorial you will learn how to alter or modify an existing table using SQL. ![]()
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