postgres doc

Author: divyagh

postgresql.md

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+# PostgreSQL online editor
+Write, Run & Share PostgreSQL queries online using OneCompiler's PostgreSQL online editor and compiler for free. It's one of the robust, feature-rich online editor and compiler for PostgreSQL. Getting started with the OneCompiler's PostgreSQL editor is really simple and pretty fast. The editor shows sample boilerplate code when you choose database as 'PostgreSQL' and start writing queries to learn and test online without worrying about tedious process of installation.
+
+# About PostgreSQL
+
+PostgreSQL is a open source relational database system and is also knows as Postgres. 
+
+### Key Features:
+
+* Postgres is not only free and open-source but also it is highly extensible. 
+* Custom Data types and funtions from various programming languaues can be introduced and the good part is compiling entire database is not required.
+* ACID(Atomicity, Consistency, Isolation, Durability) compliant.
+* First DBMS which implemented Multi-version concurrency control (MVCC) feature.
+* It's the default database server for MacOS.
+* It supports all major operating systems like Linux, Windows, OpenBSD,FreeBSD etc.
+
+# Syntax help
+
+## 1. CREATE
+CREATE command is used to create a table, schema or an index.
+#### Syntax:
+```sql
+         CREATE TABLE table_name (
+                column1 datatype,
+                column2 datatype,
+                ....);
+``` 
+## 2. ALTER
+ ALTER command is used to add, modify or delete columns or constraints from the database table.
+        
+#### Syntax
+```sql 
+ALTER TABLE Table_name ADD column_name datatype;
+```
+## 3. TRUNCATE: 
+ TRUNCATE command is used to delete the data present in the table but this will not delete the table.
+#### Syntax
+```sql
+TRUNCATE table table_name;
+```
+## 4. DROP
+DROP command is used to delete the table along with its data.
+
+#### Syntax
+```sql 
+DROP TABLE table_name;
+```
+## 5. RENAME
+RENAME command is used to rename the table name.
+
+#### Syntax
+```sql
+ALTER TABLE table_name1 RENAME to new_table_name1; 
+```
+
+## 6. INSERT
+INSERT Statement  is used to insert new records into the database table.
+#### Syntax
+```sql
+INSERT INTO table_name (column1, column2, column3, ...) VALUES (value1, value2, value3, ...);
+```
+
+## 7. SELECT
+Select statement is used to select data from database tables.
+
+####   Syntax:
+```sql
+SELECT column1, column2, ...
+FROM table_name; 
+```   
+## 8. UPDATE
+UPDATE statement is used to modify the existing values of records present in the database table.
+
+#### Syntax
+```sql
+UPDATE table_name
+SET column1 = value1, column2 = value2, ...
+WHERE condition; 
+```
+## 9. DELETE
+DELETE statement is used to delete the existing records present in the database table.
+
+#### Syntax
+```sql 
+DELETE FROM table_name where condition;
+```