An ALTER statement in SQL changes the properties of an object inside of a relational database management system (RDBMS). The types of objects that can be altered depends on which RDBMS is being used. Wikibooks has more about this subject: SQL Headline text Hello BTEC Group! History A seminal paper, A Relational Model of Data for Large Shared Data Banks, by Dr. Edgar F. Codd, was published in June, 1970 in the Association for Computing Machinery (ACM) journal, Communications of the ACM. Codds... A relational database management system (RDBMS) is a database management system (DBMS) that is based on the relational model as introduced by Edgar F. Codd. ...
The typical usage is ALTER objecttypeobjectnameparameters. For example, the command to add a column named bubbles to an existing table named sink would be:
ALTER TABLE acquires a schema modify lock on the table to ensure no other connections reference even the metadata for the table during the change.
If ALTER COLUMN changes the data type of a column to a user-defined data type that is bound to a rule, the rule bound to the new data type is not bound to the column.
ALTER TABLE permissions default to the table owner, members of the sysadmin fixed server role, and to members of the db_owner and db_ddladmin fixed database roles.
SQL, (or Structured Query Language, also pronounced as "S-Q-L", or like the word "sequel" for short) is the collection of commands that are used to manipulate a database.
It is customary that SQL commands are typed in CAPS, although most DBMS clients are case-insensitive.
This summary was written to be a guide for those new to working with SQL, and a reference for those who are still learning.
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