PostgreSQL TRANSACTION_TIMESTAMP Date/Time Function

PostgreSQL TRANSACTION_TIMESTAMP Date/Time Function

The PostgreSQL TRANSACTION_TIMESTAMP function is used to retrieve the current date and time with time zone at the start of the current transaction. This function is essential for obtaining the precise timestamp of when the current transaction begins.

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Syntax

TRANSACTION_TIMESTAMP()

The TRANSACTION_TIMESTAMP function does not take any arguments and returns a timestamp with time zone representing the current date and time at the start of the current transaction.

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Example PostgreSQL TRANSACTION_TIMESTAMP Queries

Let's look at some examples of PostgreSQL TRANSACTION_TIMESTAMP function queries:

1. Basic TRANSACTION_TIMESTAMP Example

SELECT TRANSACTION_TIMESTAMP() AS transaction_start_time;

This query retrieves the current date and time with time zone at the start of the current transaction.

2. TRANSACTION_TIMESTAMP with Column Values

SELECT id, name, TRANSACTION_TIMESTAMP() AS query_time
FROM people;

This query retrieves the id, name, and the current date and time with time zone at the start of the current transaction for each row in the people table.

3. TRANSACTION_TIMESTAMP in Conditional Statements

SELECT id, name
FROM events
WHERE event_time > TRANSACTION_TIMESTAMP();

This query retrieves the id and name of events that are scheduled to occur after the current date and time with time zone at the start of the current transaction.

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Full Example

Let's go through a complete example that includes creating a table, inserting data, and using the TRANSACTION_TIMESTAMP function to capture the current date and time at the start of the transaction.

Step 1: Creating a Table

This step involves creating a new table named people to store people's data.

CREATE TABLE people (
    id SERIAL PRIMARY KEY,
    name TEXT
);

In this example, we create a table named people with columns for id and name.

Step 2: Inserting Data into the Table

This step involves inserting some sample data into the people table.

INSERT INTO people (name)
VALUES ('Alice'),
       ('Bob'),
       ('Charlie');

Here, we insert data into the people table.

Step 3: Using the TRANSACTION_TIMESTAMP Function

This step involves using the TRANSACTION_TIMESTAMP() function to capture the current date and time during the execution of queries.

Retrieve current transaction start timestamp:

SELECT TRANSACTION_TIMESTAMP() AS transaction_start_time;

This query retrieves the current date and time with time zone at the start of the current transaction.

Capture current transaction start timestamp with column values:

SELECT id, name, TRANSACTION_TIMESTAMP() AS query_time
FROM people;

This query captures the current date and time with time zone at the start of the current transaction for each row in the people table.

Retrieve events occurring after the current transaction start timestamp:

SELECT id, name
FROM events
WHERE event_time > TRANSACTION_TIMESTAMP();

This query retrieves the id and name of events that are scheduled to occur after the current date and time with time zone at the start of the current transaction.

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Conclusion

The PostgreSQL TRANSACTION_TIMESTAMP() function is a fundamental tool for retrieving the current date and time with time zone at the start of the current transaction. Understanding how to use the TRANSACTION_TIMESTAMP() function and its syntax is essential for accurate time-based operations in PostgreSQL databases.