Dropping Tables¶ Let us go through the details related to dropping tables. We can drop table using DROP TABLE. All the direct dependent objects such as indexes, primary key constraints, unique constraints, not null constraints will automatically be dropped. Sequences will be dropped only if the sequence is owned by the column. If there are …
Truncating Tables¶ Let us understand details related to truncating tables. If you want to delete the data from a table entirely, then TRUNCATE is the fastest way to do so. Irrespective of size of the table, data can be cleaned up with in no time. Truncate operations can be rolled back. TRUNCATE is a DDL …
Overview of Sequences¶ Let us go through some of the important details related to sequences. For almost all the tables in relational databases we define primary key constraints. Primary key is nothing but unique constraint with not null and there can be only one primary key in any given table. Many times, we might not …
Indexes for Constraints¶ Let us understand details related to indexes for constraints. Constraints such as primary key and unique are supported by indexes. Primary Key – Unique and Not Null. Unique – Unique and can be null. Unless data is sorted, we need to perform full table scan to enforce uniqueness. Almost all the databases …
Indexes on Tables¶ Let us go through the details related to indexes supported in RDBMS such as Postgres. An index can be unique or non unique. Unique Index – Data will be sorted in ascending order and uniqueness is enforced. Non Unique Index – Data will be sorted in ascending order and uniqueness is not …
Managing Constraints¶ Let us understand how we can manage constraints. We can add constraints while creating the tables or after creating the tables. Constraints such as NOT NULL, CHECK, FOREIGN KEY are automatically dropped when we drop the table. Even PRIMARY KEY and UNIQUE constraints are dropped if they are not used to enforce constraints. …
