Locks for DDL Operations

Data definition language (DDL) operations include CREATE, DROP, and ALTER.

DDL operations on a given table or index lock out all other readers and writers from any table being modified. This approach is crucial to the accuracy of query results. It ensures, for example, that a table column does not disappear from the database while you are selecting data from that column.

CREATE, DROP, and ALTER commands have the following special properties:
Related concepts
Data Storage
Dbspace Management Example
Disk Space
Versioning of Temporary Tables
Multiple Writers and Readers in a Database
Related tasks
Disconnecting All Connections from a Database in Interactive SQL