Postgres and Open Source Experts

PostgreSQL offers several built-in functions to find duplicate rows/records from a table, such as ROW_NUMBER() and COUNT().

PostgreSQL doesn’t support the ISNULL function. To achieve the functionality of the ISNULL function in Postgres, COALESCE function and CASE expressions are used.

NULLIF takes some arguments and returns a NULL value if both arguments are equal or if one of them is NULL, and it returns first argument if both arguments are not equal.

NOT EXISTS operator negates the working of the EXISTS operator. It returns TRUE if the subquery returns zero rows and FALSE if the subquery returns at least one row.

In Postgres, the EXISTS operator takes a subquery as an argument and checks the existence of a record in the subquery. Consequently, it returns true or false.

In Postgres, the ELSIF is one of the decision-driven statements that evaluate several conditions. It checks/evaluates each condition one by one.

In Postgres, the if statement checks a condition/criteria and returns true or false. If statement doesn’t handle the false condition. To handle the false conditions, the else statement is used in PostgreSQL.

In PostgreSQL, the upsert feature is used either to update existing records or insert new ones into a table. The upsert feature is implemented using the INSERT ON CONFLICT statement.

PostgreSQL allows us to copy an existing table with or without data. In Postgres, either you can copy only the structure of an existing table, or you can copy a table completely along with its data.

PostgreSQL provides a built-in function named SUBSTRING() that extracts a substring from any specific string. The SUBSTRING() function accepts three parameters: a string, starting position, and length. The starting position” and “length” parameters are optional that can be skipped depending on the situation.

This write-up will present a detailed overview of extracting a substring from a string using the PostgreSQL SUBSTRING() function. So, let's get started.

How to Use SUBSTRING() …