Add PostgreSQL-Compatibility, SQL Feature Coverage, PG Extensions

docs/content/latest/api/ysql/pg-extensions.md

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+---
+title: PostgreSQL extensions
+headerTitle: PostgreSQL extensions
+linkTitle: PostgreSQL extensions
+description: List of supported PostgreSQL extensions
+summary: Reference for YSQL extensions
+menu:
+  latest:
+    identifier: api-ysql-postgresql-extensions
+    parent: api-ysql
+    weight: 4400
+isTocNested: true
+showAsideToc: true
+---
+
+PostgreSQL provides a way to extend the functionality of a database by bundling SQL objects into a package and using them as a unit. 
+This page describes the PostgreSQL extensions and describes the extensions supported by YugabyteDB.
+
+
+# PostgreSQL extensions supported by YugabyteDB
+For information about using a specific extension, see the documentation link in one of the tables below.
+ Extension | Status |  Description
+-----------|-----------|---------
+[fuzzystrmatch](https://www.postgresql.org/docs/current/fuzzystrmatch.html)  | Bundled | The fuzzystrmatch module provides several functions to determine similarities and distance between strings.
+[orafce](https://github.com/orafce/orafce)| Bundled |The orafce extension provides compatibility with Oracle functions and packages that are either missing or implemented differently in YugabyteDB and PostgreSQL. This compatibility layer can help you port your Oracle applications to YugabyteDB.
+[pgcrypto](https://www.postgresql.org/docs/current/pgcrypto.html)| Bundled |The pgcrypto extension provides various cryptographic functions.
+pg_stat_statements| |
+pg_hint_plan| |
+pgaudit| |
+pg_stat_monitor| |
+spi module| |
+uuid_ossp| |
+hstore| |
+pg_trgm| |
+postgres_fdw| |
+file_fdw| |
+sslinfo| |
+
+## Using PostgreSQL extensions
+You can install only the extensions that are supported by YugabyteDB.
+
+Note: You can only install extensions on the primary instance, not the read replica. Once installed, the extension replicates to the read replica.
+
+### Installing an extension
+Before using an extension, install it:
+In the ysql shell, run the CREATE EXTENSION command.
+### Requirement for superuser privileges
+Extensions can only be created by users that are part of the superuser role?
+
+### Inter-database connections
+The target instances for connections must be in the same VPC network as the connecting instance.
+
+## Requesting support for a new extension
+You cannot create your own extensions in YugabyteDB.
+
+To request support for an extension, add a Me, too! vote for its issue in the Issue Tracker, or create a new issue there.

docs/content/latest/explore/ysql-language-features/postgresql-compatibility.md

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+---
+title: PostgreSQL Compatibility
+linkTitle: PostgreSQL Compatibility
+description: Summary of YugabyteDB's PostgreSQL Compatibility
+image: /images/section_icons/secure/create-roles.png
+menu:
+  latest:
+    identifier: explore-ysql-postgresql-compatibility
+    parent: explore-ysql-language-features
+    weight: 70
+isTocNested: true
+showAsideToc: true
+---
+YugabyteDB is a PostgreSQL compatible distributed database that supports the majority of PostgreSQL syntax. This means that existing applications built on PostgreSQL can often be migrated to YugabyteDB without changing application code.
+
+Since YugabyteDB is PostgreSQL compatible, it works with the majority of PostgreSQL database tools such as various language drivers, ORM tools, schema migration tools, and many more third-party database tools. 
+
+Since YugabyteDB is a distributed database, supporting all PostgreSQL features easily in a distributed system is not always feasible. This page documents the known list of differences between PostgreSQL and YugabyteDB. You need to consider these differences while porting an existing application to YugabyteDB.
+
+## Unsupported PostgreSQL features
+The following PostgreSQL features are not supported in YugabyteDB:
+- Passimistic locking
+- Table locks
+- [Inheritance](https://www.postgresql.org/docs/11/tutorial-inheritance.html)
+- Exclusion Constraints
+- GiST indexes
+- Kerberos/GSSAPI 
+- Events (Listen/Notify) 
+- Drop primary key
+- XML Functions
+- XA syntax
+
+## Features that differ from PostgreSQL
+- Tablespaces 
+- Logical replication is CDC 
+- Primary key (hash/range)

docs/content/latest/explore/ysql-language-features/sql-feature-support.md

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+---
+title: SQL Feature Support
+linkTitle: SQL Feature Support
+description: Summary of YugabyteDB's conformance to the SQL standard
+image: /images/section_icons/secure/create-roles.png
+menu:
+  latest:
+    identifier: explore-ysql-language-feature-support
+    parent: explore-ysql-language-features
+    weight: 50
+isTocNested: true
+showAsideToc: true
+---
+To understand which standard SQL features we support, refer below tables.
+
+### Schema operations
+
+ Operation | Supported | Details
+-----------|-----------|---------
+Altering tables | ✓ | [`ALTER TABLE`  documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_alter_table/)
+ Altering databases | ✓ | [`ALTER DATABASE` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_alter_db/)
+ Altering columns | ✗ | 
+ Altering a column's data type | ✗ | 
+ Adding columns | ✓ | [`ADD COLUMN` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_alter_table/#add-column-column-name-data-type-constraint-constraints)
+ Removing columns | ✓ | [`DROP COLUMN` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_alter_table/#drop-column-column-name-restrict-cascade)
+ Adding constraints | ✓ | [`ADD CONSTRAINT` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_alter_table/#add-alter-table-constraint-constraints)
+ Removing constraints | ✓ | [`DROP CONSTRAINT` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_alter_table/#drop-constraint-constraint-name-restrict-cascade)
+ Altering indexes | ✗ | 
+ Adding indexes | ✓ | [`CREATE INDEX` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_create_index/)
+ Removing indexes | ✗ | 
+ Altering a primary key | ✗ | 
+ Adding user-defined schemas | ✓ |  [`CREATE SCHEMA` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/ddl_create_schema/)
+ Removing user-defined schemas | ✗ | 
+ Altering user-defined schemas | ✗ |
+
+### Data types
+
+ Data type | Supported | Details
+-----------|-----------|---------
+ `ARRAY` | ✓ | [Array documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_array/)
+ `BINARY` | ✓ | [Binary documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_binary/)
+ `BIT` | ✓ |  
+ `BYTES` | ✓ | 
+ `BOOLEAN` | ✓ | [Boolean documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_bool/)
+ `CHAR`, `VARCHAR`, `TEXT` | ✓ | [Character data types documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_character/)
+ `COLLATE` | ✓ | [Collate documentation](https://docs.yugabyte.com/latest/explore/ysql-language-features/advanced-features/collations/#root)
+ `DATE`, `TIME`, `TIMESTAMP`, `INTERVAL` | ✓ | [Date and time data types documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_datetime/)
+ `DEC`, `DECIMAL`, `NUMERIC` | ✓ | [ Fixed point numbers documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_numeric/#fixed-point-numbers)
+ `ENUM` | ✓ |[ENUM documentation](https://docs.yugabyte.com/latest/explore/ysql-language-features/data-types/#enumerations-enum-type)
+ `FLOAT`, `REAL`, `DOUBLE PRECISION` | ✓ | [Floating point numbers documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_numeric/)
+ `JSON`, `JSONB` | ✓ | [JSON data types documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_json/)
+ `MONEY` | ✓ | [Money data type documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_money/)
+ `SERIAL`, `SMALLSERIAL`, `BIGSERIAL`| ✓ | [Serial documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_serial/)
+ `SET`| ✗ | 
+ `SMALLINT, INT, INTEGER, BIGINT` | ✓ | [Integers documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_numeric/)
+ `INT4RANGE`, `INT8RANGE`, `NUMRANGE`, `TSRANGE`, `TSTZRANGE`, `DATERANGE` | ✓ | [Range data types documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_range/)
+ `UUID` | ✓ | [UUID documentation](https://docs.yugabyte.com/latest/api/ysql/datatypes/type_uuid/)
+ `XML`| ✗ | 
+ `TSVECTOR` | ✓ |
+ UDT | ✓ |
+
+### Indexes
+
+ Component | Supported |  Details
+-----------|-----------|---------
+ Indexes | ✓ | [Indexes documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/overview/)
+ GIN indexes | ✓ | [GIN Indexes documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/gin/)
+ Partial indexes | ✓ | [Partial indexes documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/partial-index-ysql/)
+ Expression indexes | ✓ | [Expression indexes](https://docs.yugabyte.com/latest/explore/indexes-constraints/expression-index-ysql/)
+ Multi-column indexes | ✗  |
+ Covering indexes | ✗  | 
+ Spatial indexes | ✗  |
+ Multiple indexes per query | ✗ |
+ Full-text indexes | ✗ | 
+ Prefix indexes | ✗ | Implement using [Expression indexes](https://docs.yugabyte.com/latest/explore/indexes-constraints/expression-index-ysql/)
+ Hash indexes | ✓ | 
+ GiST indexes | ✗ | 
+ BRIN indexes | ✗ | 
+
+### Constraints
+
+ Feature | Supported |  Details
+-----------|-----------|---------
+ Check | ✓ | [Check documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/other-constraints/#check-constraint)
+ Unique | ✓ | [Unique documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/other-constraints/#unique-constraint)
+ Not Null | ✓ | [Not Null documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/other-constraints/#not-null-constraint)
+ Primary Key | ✓ | [Primary Key documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/primary-key-ysql/)
+ Foreign Key | ✓ | [Foreign Key documentation](https://docs.yugabyte.com/latest/explore/indexes-constraints/foreign-key-ysql/)
+ Default Value | ✗ | 
+
+### Transactions
+
+ Feature | Supported | Details
+-----------|-----------|---------
+ Transactions | ✓ | [Transactions documentation](https://docs.yugabyte.com/latest/explore/transactions/)
+ `BEGIN` | ✓ | [`BEGIN` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/txn_begin/)
+ `COMMIT` | ✓ | [`COMMIT` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/txn_commit/)
+ `ROLLBACK` | ✓ | [`ROLLBACK` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/txn_rollback/)
+ `SAVEPOINT` | ✓ |  [`SAVEPOINT` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/savepoint_create/)
+ `ROLLBACK TO SAVEPOINT` | ✓ |  [`ROLLBACK TO SAVEPOINT` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/savepoint_create/)
+
+### Roles and Permissions
+
+ Component | Supported | Details
+-----------|-----------|---------
+ Users | ✓ | 
+ Roles | ✓ | 
+ Object ownership | ✓ | 
+ Privileges | ✓ | 
+ Default privileges | ✗ |
+ RLS/CLS | |
+
+### Advanced statements (other than common statementes)
+
+Statement | Supported |  Details
+-----------|-----------|---------
+ `SELECT INTO` | ✗|
+ `SELECT FOR UPDATE` | ✗ | 
+ `EXPLAIN` | ✓ | [`EXPLAIN` documentation](https://docs.yugabyte.com/latest/api/ysql/the-sql-language/statements/perf_explain)
+
+### Clauses
+
+ Clause | Supported | Details
+-----------|-----------|---------
+ `LIMIT` | ✗ | 
+ `LIMIT` with `OFFSET` | ✗ | 
+ `RETURNING` | ✗ | 
+
+### Table expressions
+
+ Component | Supported |  Details
+-----------|-----------|---------
+ Table and View references | ✓ | 
+ `AS` in table expressions | ✓ | 
+ `JOIN` (`INNER`, `LEFT`, `RIGHT`, `FULL`, `CROSS`) |✓ |  
+ Sub-queries as table expressions | ✓ | 
+ Table generator functions | ✓ | 
+ `WITH ORDINALITY` | ✓ | 
+
+### Scalar expressions and Boolean formulas
+
+ Component | Supported |  Details
+-----------|-----------|---------
+ Common functions | ✓ | 
+ Common operators | ✓ | 
+ `IF`/`CASE`/`NULLIF` | ✓ |
+ `COALESCE`/`IFNULL` | ✓ | 
+ `AND`/`OR` | ✓ | 
+ `LIKE`/`ILIKE`  | ✓ |
+ `SIMILAR TO` | ✓ |
+ Matching using POSIX regular expressions  | ✓ |
+ `EXISTS` | ✓ |
+ Scalar subqueries | ✓ |
+ Bitwise arithmetic | ✓ |
+ `COLLATE`| ✓ | 
+ Column ordinal references | ✓ |
+ Type annotations | ✓ |
+
+### Miscellaneous
+
+ Component | Supported | Details
+-----------|-----------|---------
+ Column families | ✓ | 
+ Computed columns (stored and virtual) | ✓ |
+ `ON UPDATE` expressions | ✓ |
+ Multi-region capabilities | ✓ | 
+ System catalog schemas | ✓ | 
+ Sequences |  ✓ | 
+ Identity columns | ✓ |
+ Views | ✓ | 
+ Materialized views | ✓ | 
+ Window functions | ✓ | 
+ Common table expressions | ✓|
+ Stored procedures | ✓ | 
+ Cursors | ✓ | 
+ Triggers | ✓ |