![Drop database
Once a database is no longer needed, you can delete it by using the DROP DATABASE
statement. The following illustrates the syntax of the DROP DATABASE statement:
DROP DATABASE [IF EXISTS] name;
The DROP DATABASE statement deletes catalog entries and data directory permanently. This
action cannot be undone so you have to use it with caution.
Only the database owner can execute the DROP DATABASE statement. In addition, you
cannot execute the DROP DATABASE statement if there is any active connection to the
database. You have to connect to another database e.g., postgresqlto execute the DROP
DATABASE statement.
PostgreSQL also provides a utility program named dropdbthat allows you to remove a
database. The dropdbprogram executes the DROP DATABASE statement behind the scenes](https://image.slidesharecdn.com/postgresql1-180405140707/85/Postgresql-9-320.jpg)
![Important Queries
INSERT QUERY :
INSERT INTO TABLE_NAME (column1, column2, column3,...columnN)
VALUES (value1, value2, value3,...valueN);
INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN);
SELECT QUERY : SELECT column1, column2, columnN FROM table_name;
UPDATE QUERY :
UPDATE table_name
SET column1 = value1, column2 = value2...., columnN = valueN
WHERE [condition];
DELETE QUERY:
DELETE FROM table_name](https://image.slidesharecdn.com/postgresql1-180405140707/85/Postgresql-14-320.jpg)
Postgresql
- 1. Postgresql The world's most advanced open source database
- 2. Agenda History of Postgresql Why Postgresql? Basic operations in Postgresql Advanced features of Postgresql Postgresql vs Mysql Code Snippets Questions
- 3. History 1. PostgreSQL (or Postgres) began its life in 1986 as POSTGRES, a research project of the University of California at Berkeley 2. Improved upon INGRES, an earlier prototype project also led by Stonebraker, principally through the support of user defined types (or âdomainsâ) with arbitrarily complex business rules and other object-relational concepts 3. PostgreSQL started at version 6, for consistency with the Berkeley versioning 4. 7.* line was marked by enhancements and advanced developer-focused features.It was the 8.* line, lasting from 2004 - 2009, brought features like Windowing functions and Common Table Expressions 5. 9.* line represents a turning point for the PostgreSQL community, for a number of reasons; principally, in the mind of most users, for 9.0âs introduction of simple, out of the box streaming binary replication. 6. Stable release: 10.3 / 1 March 2018
- 4. Why Postgresql ? 1. PostgreSQL isn't just relational, it's object-relational.it's object-relational. This gives it some advantages over other open source SQL databases like MySQL, MariaDB and Firebird. 2. A fundamental characteristic of an object-relational database is support for user- defined objects and their behaviors including data types, functions, operators, domains and indexes.Complex data structures can be created, stored and retrieved 3. PostgreSQL provides for storing different network address types. The CIDR (Classless Internet Domain Routing) data type follows the convention for IPv4 and IPv6 network addresses 4. Because PostgreSQL is an object-relational database, arrays of values can be stored for most of the existing data types. Do this by appending square brackets to the data type specification for the column or by using the ARRAY expressionMySQL, MariaDB, and Firebird do not have this capability
- 5. Why Postgresql ? (..continued) 5. PostgreSQL has long supported a variety of geometric data types such as points, lines, circles, and polygons. The PATH data type is one of these. A path consists of multiple points in a sequence and can be open . 6. PostgreSQL's JSON support lets you go schema-less in a SQL database. 7. The JSON data type enforces valid JSON which allows you to then make use of the specialized JSON operators and functions built into PostgreSQL for querying and manipulating the data. Also available is the JSONB type - a binary form of JSON 8. If PostgreSQL's extensive list of existing data types wasn't enough, you can use the CREATE TYPE command to create new data types as composite, enumerated, range and base
- 6. ROLES , PREVILIGES AND SCHEMA PostgreSQL uses the roles concept to manage database access permissions. A role can be a user or a group, depending on how you setup the role. A role that has login right is called user. A role may be a member of other roles, which are known as groups. CREATE ROLE role_name; Role attributes The attributes of a database role define roleâs privileges including login, superuser, database creation, role creation, password, etc. CREATE ROLE doe WITH PASSWORD 'pgSecpas1970' VALID UNTIL '2020-01-01'; Role membership It is easier to manage roles as a group so that you can grant or revoke privileges from a group as a whole. In PostgreSQL, you create a role that represents a group, and then grant membership in the group role to individual user roles.
- 7. ROLES , PREVILIGES AND SCHEMA Notice that PostgreSQL does not allow you to have circular membership loops, in which a role is the member of another role and vice versa. To restore the original privilege, you can use the following statement: RESET ROLE; Removing roles You can use the DROP ROLE statement to remove a group role or user role. DROP ROLE role_name;
- 8. Create Database To create a new PostgreSQL database, you use CREATE DATABASE statement as shown below: CREATE DATABASE db_name OWNER = role_name TEMPLATE = template ENCODING = encoding LC_COLLATE = collate LC_CTYPE = ctype TABLESPACE = tablespace_name CONNECTION LIMIT = max_concurrent_connection
- 9. Drop database Once a database is no longer needed, you can delete it by using the DROP DATABASE statement. The following illustrates the syntax of the DROP DATABASE statement: DROP DATABASE [IF EXISTS] name; The DROP DATABASE statement deletes catalog entries and data directory permanently. This action cannot be undone so you have to use it with caution. Only the database owner can execute the DROP DATABASE statement. In addition, you cannot execute the DROP DATABASE statement if there is any active connection to the database. You have to connect to another database e.g., postgresqlto execute the DROP DATABASE statement. PostgreSQL also provides a utility program named dropdbthat allows you to remove a database. The dropdbprogram executes the DROP DATABASE statement behind the scenes
- 10. Create Table To create a new PostgreSQL database, you use CREATE DATABASE statement as shown below: CREATE TABLE table_name ( column_name TYPE column_constraint, table_constraint table_constraint ) INHERITS existing_table_name; PostgreSQL table constraints 1. UNIQUE (column_list)â to force the value stored in the columns listed inside the parentheses to be unique. 2. PRIMARY KEY(column_list) â to define the primary key that consists of multiple columns. 3. CHECK (condition) â to check a condition when inserting or updating data. 4. REFERENCESâ to constrain the value stored in the column that must exist in a column in another table.
- 11. Update table To change the values of the columns in a table, you use the UPDATE statement. The following illustrates the syntax of the UPDATE statement: UPDATE table SET column1 = value1, column2 = value2 ,... WHERE condition; You can also update data of a column from another column within the same table UPDATE tableName SET column2 = column1; Sometimes, you need to update data of a table based on values in another table. In this case, you can use the PostgreSQL UPDATE join syntax as follows: UPDATE A SET A.c1 = expresion FROM B WHERE A.c2 = B.c2;
- 12. Delete table To delete data from a table, you use PostgreSQL DELETE statement as shown below: DELETE FROM table WHERE condition;
- 13. PostgreSQL - Schema A schema is a named collection of tables. A schema can also contain views, indexes, sequences, data types, operators, and functions. Schemas are analogous to directories at the operating system level, except that schemas cannot be nested CREATE SCHEMA name; The basic syntax to create table in schema is as follows â CREATE TABLE myschema.mytable ( ... ); To drop a schema use the command DROP SCHEMA myschema CASCADE;
- 14. Important Queries INSERT QUERY : INSERT INTO TABLE_NAME (column1, column2, column3,...columnN) VALUES (value1, value2, value3,...valueN); INSERT INTO TABLE_NAME VALUES (value1,value2,value3,...valueN); SELECT QUERY : SELECT column1, column2, columnN FROM table_name; UPDATE QUERY : UPDATE table_name SET column1 = value1, column2 = value2...., columnN = valueN WHERE [condition]; DELETE QUERY: DELETE FROM table_name
- 15. MVCC 1. One of the big selling points of Postgres is how it handles concurrency. The promise is simple: reads never block writes and vice versa. Postgres achieves this via a mechanism called Multi Version Concurrency Control. This technique is not unique to Postgres: there are several databases that implement some form of MVCC including Oracle, Berkeley DB, CouchDB and many more. Understanding how MVCC is implemented in Postgres is important when designing highly concurrent apps on PostgreSQL 2. Every transaction in postgres gets a transaction ID called XID. This includes single one statement transactions such as an insert, update or delete, as well as explicitely wrapping a group of statements together via BEGIN - COMMIT. When a transaction starts, Postgres increments an XID and assigns it to the current transaction. Postgres also stores transaction information on every row in the system, which is used to determine whether a row is visible to the transaction
- 16. PostgreSQL vs MySQL PostgreSQL is ACID compliant from ground up and ensures that all requirements are met. MySQL is only ACID compliant when using InnoDB and NDB Cluster Storage engines. PostgreSQL is largely SQL compliant. The level of conformance for each feature is clearly laid out in Appendix D of the manual, and any deviations are clearly documented in the âReferenceâ section of the PostgreSQL manual. MySQL is partially compliant on some of the versions (e.g does not support CHECK constraints). Overall, PostgreSQL performance is utilized best in systems requiring execution of complex queries. MySQL performs well in OLAP/OLTP systems when only read speeds are required. PostgreSQL has ROLES and inherited roles to set and maintain permissions. PostgreSQL has native SSL support for connections to encrypt client/server communications. It also has Row Level Security. MySQL implements security based on Access Control Lists (ACLs) for all connections, queries, and other operations that a user may attempt to perform PostgreSQL tackles concurrency efficiently with its MVCC implementation, which achieves very high levels of concurrency. MySQL only has MVCC support in InnoDB.
- 17. PostgreSQL vs MySQL PostgreSQL tackles concurrency efficiently with its MVCC implementation, which achieves very high levels of concurrency. MySQL only has MVCC support in InnoDB. PostgreSQL supports JSON and other NoSQL features like native XML support and key-value pairs with HSTORE. It also supports indexing JSON data for faster access. MySQL has JSON data type support but no other NoSQL feature. It does not support indexing for JSON. Supports materialized views and temporary tables. Supports temporary tables but does not support materialized views. PostgreSQL supports Geospatial data via the PostGIS extension. There are dedicated types and functions for geospatial data Geospatial data support is built in. PostgreSQL has several features dedicated to extensibility. It is possible to add new types, new functions, new index types, etc. No support for extensibility.
- 19. References â http://www.postgresqltutorial.com/ â https://devcenter.heroku.com/articles/postgresql-concurrency â https://uk.dice.com/technews/advanced-features-postgresql/
- 20. Thank you