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Use alter table to modify an existing column. You can modify any number of columns in a single alter table statement. For example, this command changes the datatype of the type column in the titles table from char(12) to varchar(20) and makes it nullable:
- ALTER TABLE statement
The ALTER TABLE statement changes table attributes (column...
- ALTER TABLE statement
The ALTER TABLE statement changes table attributes (column definitions and constraints) in a table that was previously created. The syntax allows a list of alter clauses; however, only one table constraint or column constraint can be added, modified, or deleted in each ALTER TABLE statement.
28 Ιουν 2012 · To alter any table in order to change the datatype of some field : ALTER TABLE <table_name> MODIFY <column_name> <new_datatype>. For example: In order to change the datatype of any column 'emp_id' from int to varchar, you need to : ALTER TABLE employee MODIFY emp_id varchar(10)
The ALTER TABLE statement changes table attributes (column definitions, constraints, and so on) in an existing table. The database server keeps track of object dependencies in the database. Alterations to the schema of a table may impact dependent views.
To change the data type of a column in a table, use the following syntax: SQL Server / MS Access: ALTER TABLE table_name. ALTER COLUMN column_name datatype; My SQL / Oracle (prior version 10G): ALTER TABLE table_name. MODIFY COLUMN column_name datatype; Oracle 10G and later: ALTER TABLE table_name. MODIFY column_name datatype;
Description. Adds new columns to a table; drops or modifies existing columns; adds, changes, or drops constraints; changes properties of an existing table; enables or disables triggers on a table.
Multiple ADD, ALTER, DROP, and CHANGE clauses are permitted in a single ALTER. TABLE statement, separated by commas. This is a MySQL extension to standard SQL, which permits only one of each clause per ALTER TABLE statement. For example, to drop multiple columns in a single statement, do this: Press CTRL+C to copy.
