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