To add a new column to an existing table in PostgreSQL, you can use the ALTER TABLE statement. Below is the basic syntax of adding a new column: ALTER TABLE table_name ADD COLUMN new_column_name data_type; where table_name is the name of the table to which you want to add the new column. new_column_name is the…
The CREATE TABLE AS statement is used to create a new table based on the result of a query. It allows you to create a new table that holds the data returned by a SELECT query or a subset of the data from an existing table. Here’s the basic syntax of the CREATE TABLE AS…
Temporary tables are tables that are created and used for the duration of a single database session. They are typically used to store temporary or intermediate data that you need to work with within a specific session. Temporary tables are automatically dropped at the end of the session or when the connection is closed, so…
Database Users are accounts that can be used to log into the database system and perform various actions, such as querying the database, creating tables, and executing administrative tasks. PostgreSQL supports both regular users and superusers (also known as administrators). Creating a User: To create a user, you can use the CREATE USER command: CREATE…
An “upsert” operation refers to the ability to update an existing row if it exists, or insert a new row if it doesn’t exist, based on a specified condition. The upsert operation is also known as “merge” or “insert on conflict update.” INSERT INTO target_table (column1, column2, …) VALUES (value1, value2, …) ON CONFLICT (unique_constraint_columns)…
The json_populate_record function is used to populate the fields of a given composite type with data from a JSON object. This function is particularly useful when you have a JSON object that matches the structure of a composite type, and you want to extract values from the JSON and populate a composite variable. Below is…
The json_array_elements function is used to expand a JSON array into a set of rows. This function takes a JSON array as input and returns a set of rows, where each row represents an element from the input array. This is particularly useful when you want to work with individual elements of a JSON array…
In PostgreSQL, the json_each function is used to expand a JSON object into a set of key-value pairs. This function can be helpful when you want to break down a JSON object into its individual components for further analysis or manipulation. The json_each function returns a set of rows, each containing a key and its…
The json_array_length function is used to determine the number of elements in a JSON array. It’s particularly useful when you’re working with JSON data and need to find out how many items are present in an array within a JSON document. The syntax for using the json_array_length function is as follows: json_array_length(json_array) Here’s an example…
The json_object in PostgreSQL function is used to create a JSON object from a set of key-value pairs. This function was introduced in PostgreSQL 12 and provides a convenient way to create JSON objects directly within SQL queries. The basic syntax of the json_object function is as follows: json_object(key1 value1, key2 value2, …, keyN valueN)…