### Start PostgreSQL server

Source: https://devdocs.io/postgresql~18/upgrading

Start the database server using the new installation binaries.

```bash
/usr/local/pgsql/bin/postgres -D /usr/local/pgsql/data
```

--------------------------------

### Complete crosstab Example with Table Setup

Source: https://devdocs.io/postgresql~18/tablefunc

This example demonstrates creating a table, inserting data, and then using crosstab to pivot the data, defining the output columns explicitly.

```sql
CREATE TABLE ct(id SERIAL, rowid TEXT, attribute TEXT, value TEXT);
INSERT INTO ct(rowid, attribute, value) VALUES('test1','att1','val1');
INSERT INTO ct(rowid, attribute, value) VALUES('test1','att2','val2');
INSERT INTO ct(rowid, attribute, value) VALUES('test1','att3','val3');
INSERT INTO ct(rowid, attribute, value) VALUES('test1','att4','val4');
INSERT INTO ct(rowid, attribute, value) VALUES('test2','att1','val5');
INSERT INTO ct(rowid, attribute, value) VALUES('test2','att2','val6');
INSERT INTO ct(rowid, attribute, value) VALUES('test2','att3','val7');
INSERT INTO ct(rowid, attribute, value) VALUES('test2','att4','val8');

SELECT *
FROM crosstab(
  'select rowid, attribute, value
   from ct
   where attribute = ''att2'' or attribute = ''att3''
   order by 1,2')
AS ct(row_name text, category_1 text, category_2 text, category_3 text);
```

```sql
 row_name | category_1 | category_2 | category_3
----------+------------+------------+------------
 test1    | val2       | val3       | 
 test2    | val6       | val7       | 
(2 rows)
```

--------------------------------

### Benchmark Setup and Execution

Source: https://devdocs.io/postgresql~18/intarray

Provides commands to set up a test database, create the intarray extension, load test data, and run the benchmark suite. Requires DBD::Pg to be installed.

```shell
cd .../contrib/intarray/bench
createdb TEST
psql -c "CREATE EXTENSION intarray" TEST
./create_test.pl | psql TEST
./bench.pl
```

--------------------------------

### SHOW Command Examples

Source: https://devdocs.io/postgresql~18/sql-show

Examples demonstrating how to query specific parameters and all available settings.

```sql
SHOW DateStyle;
 DateStyle
-----------
 ISO, MDY
(1 row)
```

```sql
SHOW geqo;
 geqo
------
 on
(1 row)
```

```sql
SHOW ALL;
            name         | setting |                description
-------------------------+---------+-------------------------------------------------
 allow_system_table_mods | off     | Allows modifications of the structure of ...
    .
    .
    .
 xmloption               | content | Sets whether XML data in implicit parsing ...
 zero_damaged_pages      | off     | Continues processing past damaged page headers.
(196 rows)
```

--------------------------------

### Setup and query hierarchical data

Source: https://devdocs.io/postgresql~18/tablefunc

Complete example creating a tree table, inserting data, and querying it with and without branch and ordering parameters.

```sql
CREATE TABLE connectby_tree(keyid text, parent_keyid text, pos int);

INSERT INTO connectby_tree VALUES('row1',NULL, 0);
INSERT INTO connectby_tree VALUES('row2','row1', 0);
INSERT INTO connectby_tree VALUES('row3','row1', 0);
INSERT INTO connectby_tree VALUES('row4','row2', 1);
INSERT INTO connectby_tree VALUES('row5','row2', 0);
INSERT INTO connectby_tree VALUES('row6','row4', 0);
INSERT INTO connectby_tree VALUES('row7','row3', 0);
INSERT INTO connectby_tree VALUES('row8','row6', 0);
INSERT INTO connectby_tree VALUES('row9','row5', 0);

-- with branch, without orderby_fld (order of results is not guaranteed)
SELECT * FROM connectby('connectby_tree', 'keyid', 'parent_keyid', 'row2', 0, '~')
 AS t(keyid text, parent_keyid text, level int, branch text);
 keyid | parent_keyid | level |       branch
-------+--------------+-------+---------------------
 row2  |              |     0 | row2
 row4  | row2         |     1 | row2~row4
 row6  | row4         |     2 | row2~row4~row6
 row8  | row6         |     3 | row2~row4~row6~row8
 row5  | row2         |     1 | row2~row5
 row9  | row5         |     2 | row2~row5~row9
(6 rows)

-- without branch, without orderby_fld (order of results is not guaranteed)
SELECT * FROM connectby('connectby_tree', 'keyid', 'parent_keyid', 'row2', 0)
 AS t(keyid text, parent_keyid text, level int);
 keyid | parent_keyid | level
-------+--------------+-------
 row2  |              |     0
 row4  | row2         |     1
 row6  | row4         |     2
 row8  | row6         |     3
 row5  | row2         |     1
 row9  | row5         |     2
(6 rows)
```

--------------------------------

### dict_xsyn Usage and Examples

Source: https://devdocs.io/postgresql~18/dict-xsyn

Demonstrates how to install, alter, and use the dict_xsyn dictionary, including examples of ts_lexize function calls and text search configuration.

```APIDOC
## F.13.2. Usage 
Installing the `dict_xsyn` extension creates a text search template `xsyn_template` and a dictionary `xsyn` based on it, with default parameters. You can alter the parameters, for example
```sql
mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=false);
ALTER TEXT SEARCH DICTIONARY
```

or create new dictionaries based on the template.
To test the dictionary, you can try
```sql
mydb=# SELECT ts_lexize('xsyn', 'word');
      ts_lexize
-----------------------
 {syn1,syn2,syn3}

mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=true);
ALTER TEXT SEARCH DICTIONARY

mydb=# SELECT ts_lexize('xsyn', 'word');
      ts_lexize
-----------------------
 {word,syn1,syn2,syn3}

mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=false, MATCHSYNONYMS=true);
ALTER TEXT SEARCH DICTIONARY

mydb=# SELECT ts_lexize('xsyn', 'syn1');
      ts_lexize
-----------------------
 {syn1,syn2,syn3}

mydb# ALTER TEXT SEARCH DICTIONARY xsyn (RULES='my_rules', KEEPORIG=true, MATCHORIG=false, KEEPSYNONYMS=false);
ALTER TEXT SEARCH DICTIONARY

mydb=# SELECT ts_lexize('xsyn', 'syn1');
      ts_lexize
-----------------------
 {word}
```

Real-world usage will involve including it in a text search configuration as described in Chapter 12. That might look like this:
```sql
ALTER TEXT SEARCH CONFIGURATION english
    ALTER MAPPING FOR word, asciiword WITH xsyn, english_stem;
```
```

--------------------------------

### Create Tables for Publication Examples

Source: https://devdocs.io/postgresql~18/logical-replication-row-filter

Initial table setup required for demonstrating publication row filters.

```sql
/* pub # */ CREATE TABLE t1(a int, b int, c text, PRIMARY KEY(a,c));
/* pub # */ CREATE TABLE t2(d int, e int, f int, PRIMARY KEY(d));
/* pub # */ CREATE TABLE t3(g int, h int, i int, PRIMARY KEY(g));
```

--------------------------------

### Initiate a psql session

Source: https://devdocs.io/postgresql~18/app-psql

Example of starting a psql session connected to a specific database.

```shell
$ psql testdb
psql (18.3)
Type "help" for help.

testdb=>
```

--------------------------------

### List Partitioning Examples

Source: https://devdocs.io/postgresql~18/sql-createtable

Examples of creating list-partitioned tables.

```APIDOC
## CREATE TABLE cities_ab

### Description
Creates a list partition named 'cities_ab' for the 'cities' table, containing values 'a' and 'b', with a check constraint.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE cities_ab
    PARTITION OF cities (
    CONSTRAINT city_id_nonzero CHECK (city_id != 0)
) FOR VALUES IN ('a', 'b');
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

```APIDOC
## CREATE TABLE cities_ab_10000_to_100000

### Description
Creates a range partition 'cities_ab_10000_to_100000' for the list-partitioned table 'cities_ab', for population values from 10000 to 100000.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE cities_ab_10000_to_100000
    PARTITION OF cities_ab FOR VALUES FROM (10000) TO (100000);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

--------------------------------

### Drop a server example

Source: https://devdocs.io/postgresql~18/sql-dropserver

Example demonstrating how to drop a server named 'foo' if it exists.

```sql
DROP SERVER IF EXISTS foo;
```

--------------------------------

### Hash Partitioning Examples

Source: https://devdocs.io/postgresql~18/sql-createtable

Examples of creating hash-partitioned tables for the 'orders' table.

```APIDOC
## CREATE TABLE orders_p1

### Description
Creates a hash partition 'orders_p1' for the 'orders' table with MODULUS 4 and REMAINDER 0.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE orders_p1 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 0);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

```APIDOC
## CREATE TABLE orders_p2

### Description
Creates a hash partition 'orders_p2' for the 'orders' table with MODULUS 4 and REMAINDER 1.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE orders_p2 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 1);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

```APIDOC
## CREATE TABLE orders_p3

### Description
Creates a hash partition 'orders_p3' for the 'orders' table with MODULUS 4 and REMAINDER 2.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE orders_p3 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 2);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

```APIDOC
## CREATE TABLE orders_p4

### Description
Creates a hash partition 'orders_p4' for the 'orders' table with MODULUS 4 and REMAINDER 3.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE orders_p4 PARTITION OF orders
    FOR VALUES WITH (MODULUS 4, REMAINDER 3);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

--------------------------------

### SELinux Context Notification Examples

Source: https://devdocs.io/postgresql~18/sepgsql

Example of harmless notifications that may appear during installation depending on libselinux and selinux-policy versions.

```text
/etc/selinux/targeted/contexts/sepgsql_contexts:  line 33 has invalid object type db_blobs
/etc/selinux/targeted/contexts/sepgsql_contexts:  line 36 has invalid object type db_language
/etc/selinux/targeted/contexts/sepgsql_contexts:  line 37 has invalid object type db_language
/etc/selinux/targeted/contexts/sepgsql_contexts:  line 38 has invalid object type db_language
/etc/selinux/targeted/contexts/sepgsql_contexts:  line 39 has invalid object type db_language
/etc/selinux/targeted/contexts/sepgsql_contexts:  line 40 has invalid object type db_language
```

--------------------------------

### Default Partition Example

Source: https://devdocs.io/postgresql~18/sql-createtable

Example of creating a default partition for a table.

```APIDOC
## CREATE TABLE cities_partdef

### Description
Creates a default partition named 'cities_partdef' for the 'cities' table.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE cities_partdef
    PARTITION OF cities DEFAULT;
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

--------------------------------

### Start Upgraded PostgreSQL Server

Source: https://devdocs.io/postgresql~18/logical-replication-upgrade

Starts the newly upgraded PostgreSQL server instance.

```bash
pg_ctl -D /opt/PostgreSQL/data1_upgraded start -l logfile
```

```bash
pg_ctl -D /opt/PostgreSQL/data2_upgraded start -l logfile
```

--------------------------------

### Create a subscription replicating multiple publications

Source: https://devdocs.io/postgresql~18/sql-createsubscription

This example demonstrates creating a subscription that replicates tables from multiple specified publications. Replication starts immediately on commit.

```sql
CREATE SUBSCRIPTION mysub
         CONNECTION 'host=192.168.1.50 port=5432 user=foo dbname=foodb'
        PUBLICATION mypublication, insert_only;

```

--------------------------------

### CREATE ROLE Examples

Source: https://devdocs.io/postgresql~18/sql-createrole

Practical examples demonstrating the usage of the CREATE ROLE command for various scenarios.

```APIDOC
## CREATE ROLE Examples

### Description
Provides practical examples of using the `CREATE ROLE` command.

### Examples

1.  **Create a role that can log in, but without a password:**
    ```sql
    CREATE ROLE jonathan LOGIN;
    ```

2.  **Create a user with a password:**
    ```sql
    CREATE USER davide WITH PASSWORD 'jw8s0F4';
    ```
    *Note: `CREATE USER` implies `LOGIN`.*

3.  **Create a role with a password valid until a specific date:**
    ```sql
    CREATE ROLE miriam WITH LOGIN PASSWORD 'jw8s0F4' VALID UNTIL '2005-01-01';
    ```

4.  **Create a role with privileges to create databases and manage roles:**
    ```sql
    CREATE ROLE admin WITH CREATEDB CREATEROLE;
    ```
```

--------------------------------

### Start Upgraded Publisher Server

Source: https://devdocs.io/postgresql~18/logical-replication-upgrade

Command to start the upgraded PostgreSQL publisher server on node1.

```bash
pg_ctl -D /opt/PostgreSQL/data1_upgraded start -l logfile
```

--------------------------------

### Example pg_basebackup Module

Source: https://devdocs.io/postgresql~18/btree-gist

This is an example module for pg_basebackup, demonstrating shell integration for backup operations.

```sql
basic_archive — an example WAL archive module
```

--------------------------------

### Install extension using search path

Source: https://devdocs.io/postgresql~18/sql-createextension

Sets the search path to the target schema before installing the extension.

```sql
SET search_path = addons;
CREATE EXTENSION hstore;
```

--------------------------------

### Example pg_basebackup Shell Module

Source: https://devdocs.io/postgresql~18/btree-gist

This is an example module for pg_basebackup that integrates with the shell environment.

```sql
basebackup_to_shell — example "shell" pg_basebackup module
```

--------------------------------

### Execute Tutorial Scripts

Source: https://devdocs.io/postgresql~18/tutorial-sql-intro

Start the psql session in single-step mode and load the tutorial SQL file.

```bash
$ **psql -s mydb**

...

mydb=> **\i basics.sql**
```

--------------------------------

### Get Backend Start Time

Source: https://devdocs.io/postgresql~18/monitoring-stats

Returns the timestamp indicating when the specified backend process was started.

```sql
pg_stat_get_backend_start(integer)
```

--------------------------------

### Manual directory setup and cluster initialization

Source: https://devdocs.io/postgresql~18/creating-cluster

Demonstrates the process of creating a parent directory, assigning ownership to the postgres user, and initializing the cluster.

```bash
root# **mkdir /usr/local/pgsql**
root# **chown postgres /usr/local/pgsql**
root# **su postgres**
postgres$ **initdb -D /usr/local/pgsql/data**
```

--------------------------------

### Get Backend Transaction Start Time

Source: https://devdocs.io/postgresql~18/monitoring-stats

Returns the timestamp when the backend's current transaction was started.

```sql
pg_stat_get_backend_xact_start(integer)
```

--------------------------------

### Get Backend Activity Start Time

Source: https://devdocs.io/postgresql~18/monitoring-stats

Returns the timestamp when the backend's most recent query was started.

```sql
pg_stat_get_backend_activity_start(integer)
```

--------------------------------

### Compile Tutorial Files

Source: https://devdocs.io/postgresql~18/tutorial-sql-intro

Navigate to the tutorial directory and compile the necessary scripts and C files.

```bash
$ **cd .../src/tutorial**
$ **make**
```

--------------------------------

### Create a basic database

Source: https://devdocs.io/postgresql~18/sql-createdatabase

Initializes a new database with default settings.

```sql
CREATE DATABASE lusiadas;
```

--------------------------------

### Example postgresql.conf configuration

Source: https://devdocs.io/postgresql~18/config-setting

A sample snippet showing the structure of the postgresql.conf file.

```text

```

--------------------------------

### Get Token Types with Parser OID - ts_token_type

Source: https://devdocs.io/postgresql~18/functions-textsearch

Use `ts_token_type` to get a description of token types recognized by a parser specified by its OID. Provide the parser OID. Example uses OID 3722.

```sql
ts_token_type(3722)
```

--------------------------------

### Get Token Types with Named Parser - ts_token_type

Source: https://devdocs.io/postgresql~18/functions-textsearch

Use `ts_token_type` to get a description of token types recognized by a named parser. Specify the parser name. Example shows retrieving types for the 'default' parser.

```sql
ts_token_type('default')
```

--------------------------------

### Example: Listening and then Unlistening

Source: https://devdocs.io/postgresql~18/sql-unlisten

This example demonstrates how to set up a listener using LISTEN, send a notification with NOTIFY, and then stop listening with UNLISTEN. After UNLISTEN, further NOTIFY messages on that channel are ignored.

```sql
LISTEN virtual;
NOTIFY virtual;
Asynchronous notification "virtual" received from server process with PID 8448.

UNLISTEN virtual;
NOTIFY virtual;
-- no NOTIFY event is received
```

--------------------------------

### Create a disabled subscription

Source: https://devdocs.io/postgresql~18/sql-createsubscription

This example shows how to create a subscription that does not start replicating immediately. It can be enabled later using ALTER SUBSCRIPTION.

```sql
CREATE SUBSCRIPTION mysub
         CONNECTION 'host=192.168.1.50 port=5432 user=foo dbname=foodb'
        PUBLICATION insert_only
               WITH (enabled = false);

```

--------------------------------

### Generate Date Series with Interval

Source: https://devdocs.io/postgresql~18/functions-srf

Generates a series of dates by adding a specified interval to a start date. This example uses the date-plus-integer operator.

```sql
SELECT current_date + s.a AS dates FROM generate_series(0,14,7) AS s(a);
```

--------------------------------

### CREATE SEQUENCE Syntax and Examples

Source: https://devdocs.io/postgresql~18/sql-createsequence

Demonstrates how to create sequences with different options and use them in SQL commands.

```APIDOC
## CREATE SEQUENCE

### Description
Creates a new sequence object. Sequences are typically used to generate unique identifiers for rows in a table.

### Method
SQL Statement

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
N/A

#### Query Parameters
N/A

#### Request Body
N/A

### Request Example
```sql
CREATE SEQUENCE serial START 101;
```

### Response
#### Success Response (0)
Sequence created successfully.

#### Response Example
N/A

## Using Sequences

### Description
Examples of how to use sequences to generate unique numbers for inserts and updates.

### Method
SQL Statement

### Endpoint
N/A (SQL Command)

### Parameters
N/A

### Request Example
```sql
-- Select the next number from a sequence
SELECT nextval('serial');

-- Use sequence in an INSERT statement
INSERT INTO distributors VALUES (nextval('serial'), 'nothing');

-- Update sequence value after a COPY FROM command
BEGIN;
COPY distributors FROM 'input_file';
SELECT setval('serial', max(id)) FROM distributors;
END;
```

### Response
#### Success Response (200)
Returns the next sequence value or confirms statement execution.

#### Response Example
```
 nextval
---------
     101
```

## Sequence Properties and Limitations

### Description
Details on sequence data types, range, and behavior with caching and concurrent access.

### Method
N/A (Conceptual Information)

### Endpoint
N/A

### Parameters
N/A

### Request Example
N/A

### Response
#### Success Response (0)
Provides information about sequence characteristics.

#### Response Example
Sequences are based on `bigint` arithmetic, with a range from -9223372036854775808 to 9223372036854775807. `nextval` and `setval` calls are never rolled back. Using `cache` greater than one can lead to gaps in sequence numbers when multiple sessions access the sequence concurrently.
```

--------------------------------

### Extracting Substrings with regexp_substr

Source: https://devdocs.io/postgresql~18/functions-matching

Examples demonstrating the use of regexp_substr to extract specific matches from a string based on pattern, start position, and occurrence index.

```sql
regexp_substr('number of your street, town zip, FR', '[^,]+', 1, 2)
```

```sql
regexp_substr('ABCDEFGHI', '(c..)(...)', 1, 1, 'i', 2)
```

--------------------------------

### Creating a Foreign Table with file_fdw

Source: https://devdocs.io/postgresql~18/file-fdw

Example demonstrating how to install the file_fdw extension, create a foreign server, and then define a foreign table to access CSV log files.

```APIDOC
## Creating a Foreign Table with file_fdw

### Description
This example shows the steps to set up and use the `file_fdw` to access PostgreSQL CSV logs.

### Steps

1.  **Install the extension:**
    ```sql
    CREATE EXTENSION file_fdw;
    ```

2.  **Create a foreign server:**
    ```sql
    CREATE SERVER pglog FOREIGN DATA WRAPPER file_fdw;
    ```

3.  **Create the foreign data table:**
    Define the columns, the CSV file name, and its format.
    ```sql
    CREATE FOREIGN TABLE pglog (
      -- column definitions here
    ) SERVER pglog
    OPTIONS (
      filename 'pglog.csv',
      format 'csv',
      header 'true'
      -- other options as needed
    );
    ```
```

--------------------------------

### Get Backend PIDs and Queries

Source: https://devdocs.io/postgresql~18/monitoring-stats

Retrieves the process IDs (PIDs) and current queries for all active backend processes. This example demonstrates using pg_stat_get_backend_idset() in conjunction with other per-backend statistics functions.

```sql
SELECT pg_stat_get_backend_pid(backendid) AS pid,
       pg_stat_get_backend_activity(backendid) AS query
FROM pg_stat_get_backend_idset() AS backendid;
```

--------------------------------

### Modular PostgreSQL Configuration Example

Source: https://devdocs.io/postgresql~18/config-setting

This example demonstrates how to use multiple `include` directives to break down configuration into shared, memory-specific, and server-specific files. The order of inclusion matters as later settings can override earlier ones.

```postgresql
include 'shared.conf'
include 'memory.conf'
include 'server.conf'
```

--------------------------------

### Configure extension and library paths together

Source: https://devdocs.io/postgresql~18/runtime-config-client

Example of setting both extension and library paths to include nonstandard locations.

```text
extension_control_path = '/usr/local/share/postgresql:$system'
dynamic_library_path = '/usr/local/lib/postgresql:$libdir'
```

--------------------------------

### Initialize pgbench Database

Source: https://devdocs.io/postgresql~18/pgbench

Use the -i option to create and populate the necessary tables for the default benchmark. Ensure you use a separate database to avoid data loss.

```bash
pgbench -i [ other-options ] dbname
```

--------------------------------

### Get Database Object Comment by OID and Catalog in PostgreSQL

Source: https://devdocs.io/postgresql~18/functions-info

Retrieves the comment for a database object identified by its OID and the name of its system catalog. Example: retrieving a comment for a table with OID 123456.

```sql
obj_description(123456, 'pg_class')
```

--------------------------------

### PostgreSQL Query With JIT Enabled

Source: https://devdocs.io/postgresql~18/jit-decision

This example demonstrates the output of EXPLAIN ANALYZE after adjusting JIT cost settings. It shows that JIT compilation was used, including details on functions, options, and timing, even though inlining and optimization were not applied.

```sql
#= EXPLAIN ANALYZE SELECT SUM(relpages) FROM pg_class;
                                                 QUERY PLAN
-------------------------------------------------------------------​------------------------------------------
 Aggregate  (cost=16.27..16.29 rows=1 width=8) (actual time=6.049..6.049 rows=1.00 loops=1)
   Buffers: shared hit=14
   ->  Seq Scan on pg_class  (cost=0.00..15.42 rows=342 width=4) (actual time=0.019..0.052 rows=356.00 loops=1)
         Buffers: shared hit=14
 Planning Time: 0.133 ms
 JIT:
   Functions: 3
   Options: Inlining false, Optimization false, Expressions true, Deforming true
   Timing: Generation 1.259 ms (Deform 0.000 ms), Inlining 0.000 ms, Optimization 0.797 ms, Emission 5.048 ms, Total 7.104 ms
 Execution Time: 7.416 ms


```

--------------------------------

### Get Start Times of Segments with High Heart Rate

Source: https://devdocs.io/postgresql~18/functions-json

Apply a filter expression to select segments meeting a condition, then extract a specific field from the filtered results. The path within the condition is relative to the current item.

```sql
select jsonb_path_query(:'json', '$.track.segments[*] ? (@.HR > 130)."start time"')
```

--------------------------------

### Get Range of Enum Values

Source: https://devdocs.io/postgresql~18/functions-enum

Returns an ordered array of enum values between two specified enum members. If the first parameter is null, the range starts from the first enum value. If the second parameter is null, the range ends with the last enum value.

```sql
enum_range('orange'::rainbow, 'green'::rainbow)
```

```sql
enum_range(NULL, 'green'::rainbow)
```

```sql
enum_range('orange'::rainbow, NULL)
```

--------------------------------

### Create a new database with default settings

Source: https://devdocs.io/postgresql~18/app-createdb

Use this command to create a new database with the default server settings. Ensure the database server is running.

```bash
$ createdb demo
```

--------------------------------

### Rename PostgreSQL installation directory

Source: https://devdocs.io/postgresql~18/pgupgrade

Use this command to move an existing PostgreSQL installation directory to avoid conflicts with a new installation.

```bash
mv /usr/local/pgsql /usr/local/pgsql.old
```

--------------------------------

### Configure Standby Server Parameters

Source: https://devdocs.io/postgresql~18/warm-standby

Example configuration settings for a standby server, including connection information, restore commands, and archive cleanup.

```text
primary_conninfo = 'host=192.168.1.50 port=5432 user=foo password=foopass options=''-c wal_sender_timeout=5000'''
restore_command = 'cp /path/to/archive/%f %p'
archive_cleanup_command = 'pg_archivecleanup /path/to/archive %r'
```

--------------------------------

### pg_backup_start

Source: https://devdocs.io/postgresql~18/functions-admin

Prepares the server to begin an on-line backup.

```APIDOC
## pg_backup_start

### Description
Prepares the server to begin an on-line backup.

### Parameters
#### Request Body
- **label** (text) - Required - An arbitrary user-defined label for the backup.
- **fast** (boolean) - Optional - If true, forces an immediate checkpoint.
```

--------------------------------

### Range Partitioning Examples

Source: https://devdocs.io/postgresql~18/sql-createtable

Examples of creating range-partitioned tables for time-series data.

```APIDOC
## CREATE TABLE measurement_ym_y2016m11

### Description
Creates a partition for the 'measurement_year_month' table for the month of November 2016.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE measurement_ym_y2016m11
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2016, 11) TO (2016, 12);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

```APIDOC
## CREATE TABLE measurement_ym_y2016m12

### Description
Creates a partition for the 'measurement_year_month' table for the month of December 2016.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE measurement_ym_y2016m12
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2016, 12) TO (2017, 01);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

```APIDOC
## CREATE TABLE measurement_ym_y2017m01

### Description
Creates a partition for the 'measurement_year_month' table for the month of January 2017.

### Method
CREATE TABLE

### Endpoint
N/A (SQL Command)

### Parameters
#### Path Parameters
None

#### Query Parameters
None

#### Request Body
None

### Request Example
```sql
CREATE TABLE measurement_ym_y2017m01
    PARTITION OF measurement_year_month
    FOR VALUES FROM (2017, 01) TO (2017, 02);
```

### Response
#### Success Response (200)
Table created successfully.

#### Response Example
```sql
-- No specific output, table is created.
```
```

--------------------------------

### EXISTS Usage Example

Source: https://devdocs.io/postgresql~18/functions-subquery

Example of using EXISTS to perform a semi-join operation.

```sql
SELECT col1
FROM tab1
WHERE EXISTS (SELECT 1 FROM tab2 WHERE col2 = tab1.col2);
```

--------------------------------

### Substring Matching with starts with

Source: https://devdocs.io/postgresql~18/functions-json

Checks if a string value starts with the specified prefix.

```SQL
jsonb_path_query('["John Smith", "Mary Stone", "Bob Johnson"]', '$[*] ? (@ starts with "John")')
```

--------------------------------

### Create a table with multi-line input

Source: https://devdocs.io/postgresql~18/app-psql

Demonstrates how to spread a SQL command across multiple lines using the psql prompt.

```sql
testdb=> CREATE TABLE my_table (
testdb(>  first integer not null default 0,
testdb(>  second text)
testdb-> ;
CREATE TABLE
```

--------------------------------

### Install file_fdw Extension

Source: https://devdocs.io/postgresql~18/file-fdw

Installs the file_fdw extension. This is a prerequisite for using the file_fdw functionality.

```sql
CREATE EXTENSION file_fdw;
```

--------------------------------

### Example of Dynamic Domain Transition with sepgsql_setcon

Source: https://devdocs.io/postgresql~18/sepgsql

Demonstrates switching to a more restricted security context and the denial of switching back to a less restricted one. Requires the 'setcurrent' and 'dyntransition' permissions.

```sql
regression=# select sepgsql_getcon();
                    sepgsql_getcon
-------------------------------------------------------
 unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
(1 row)

regression=# SELECT sepgsql_setcon('unconfined_u:unconfined_r:unconfined_t:s0-s0:c1.c4');
 sepgsql_setcon
----------------
 t
(1 row)

regression=# SELECT sepgsql_setcon('unconfined_u:unconfined_r:unconfined_t:s0-s0:c1.c1023');
ERROR:  SELinux: security policy violation


```

--------------------------------

### Remove a Sequence Example

Source: https://devdocs.io/postgresql~18/sql-dropsequence

A basic example demonstrating how to remove a sequence named 'serial'.

```sql
DROP SEQUENCE serial;
```

--------------------------------

### DROP TABLE Example

Source: https://devdocs.io/postgresql~18/sql-droptable

Example demonstrating how to remove multiple tables in a single command.

```sql
DROP TABLE films, distributors;
```

--------------------------------

### Create a sample table

Source: https://devdocs.io/postgresql~18/indexes-intro

Defines a basic table structure for demonstrating index usage.

```sql
CREATE TABLE test1 (
    id integer,
    content varchar
);
```

--------------------------------

### Start PostgreSQL on a specific port

Source: https://devdocs.io/postgresql~18/app-postgres

Launches the server instance listening on a custom port.

```bash
postgres -p 1234
```

--------------------------------

### Pass Configuration Parameters to Postgres Server

Source: https://devdocs.io/postgresql~18/config-setting

Sets configuration parameters during server startup using command-line arguments.

```bash
postgres -c log_connections=all --log-destination='syslog'
```

--------------------------------

### Drop a Publication Example

Source: https://devdocs.io/postgresql~18/sql-droppublication

A basic example demonstrating how to remove a publication named 'mypublication'.

```sql
DROP PUBLICATION mypublication;
```