The logical framework of the database is known as a schema. In UltraLite, the schema is maintained as a catalog of system tables that hold the metadata for the UltraLite database. Metadata stored in the system tables includes:
You can change the schema of a database with the appropriate Data Definition Language (DDL) statements. If you require more than just a few changes, you can use the ALTER DATABASE SCHEMA FROM FILE statement to modify the schema definition using a SQL script.
Schema changes can take a considerable amount of time. For example, all rows in the associated table must be updated when the column type is changed. DDL statements successfully execute when there are not any:
Other active uses of the schema (for example, synchronization, prepared but unreleased statements, or executing database operations).
If either of these conditions is true, the DDL statement fails. When the DDL statement is executing, any other attempt to use the database is blocked until the DDL statements completes the schema change.
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