Avoid ALTER TABLE

Performance impact: Variable

The ALTER TABLE statement enables applications to add columns to a table and to drop columns from a table. Although the ALTER TABLE statement itself runs very quickly in most cases, the modifications it makes to the table can cause subsequent DML statements and queries on the table to run more slowly.

The actual performance degradation that the application experiences varies with the number of times the table has been altered and with the particular operation being performed on the table.

Dropping VARCHAR2 and VARBINARY columns is slower than dropping columns of other data types since a table scan is required to free the space allocated to the existing VARCHAR2 and VARBINARY values in the column to be dropped.