I have datas in df like
time | location | information |
---|---|---|
2.13 | India | Good |
2.34 | USA | Good |
I need to update this to timescale db where time is the unique key, i have used
list_db_df=df.values.tolist()
Now this turned into a list of values like
[[2.13,India,Good],[2.34,USA,Good]]
How do i write this for insert query like this,
INSERT INTO table_name
VALUES
(NOW(), 'office', 70.0, 50.0),
(NOW(), 'basement', 66.5, 60.0),
(NOW(), 'garage', 77.0, 65.2);
Basically this format
https://docs.timescale.com/timescaledb/latest/how-to-guides/write-data/insert/#insert
And need help with on conflict clause (Example)
INSERT INTO table_name
VALUES ('2017-07-28 11:42:42.846621 00', 'office', 70.2, 50.1)
ON CONFLICT (time, location) DO UPDATE
SET temperature = excluded.temperature,
humidity = excluded.humidity;
Like, what is excluded.temperature there.
Thanks in advance.
CodePudding user response:
Short
Quote from the docs
The SET and WHERE clauses in ON CONFLICT DO UPDATE have access to the existing row using the table's name (or an alias), and to rows proposed for insertion using the special excluded table.
In your example, excluded.temperature
has the value 70.2
Details
See also DbFiddle example:
Let's assume, that the table already has a row with this primary key ('2017-07-28 11:42:42.846621 00'
, office
):
time | location | temperature | humidity |
---|---|---|---|
2017-07-28 12:42:42.846621 01 | office | 60.1 | 50 |
Now we execute an insert statements (with the same primary key) and different ON CONFLICT
clauses
No ON CONFLICT
clause
INSERT INTO conditions VALUES ('2017-07-28 11:42:42.846621 00', 'office', 70.2, 50.1)
When we do not use ON CONFLICT
, we get an error:
ERROR: duplicate key value violates unique constraint "conditions_time_location_key"
DETAIL: Key ("time", location)=(2017-07-28 12:42:42.846621 01, office) already exists.
ON CONFLICT DO NOTHING
INSERT INTO conditions
VALUES ('2017-07-28 11:42:42.846621 00', 'office', 70.2, 50.1)
ON CONFLICT DO NOTHING
In this case the new data is ignored and the row remains the same as before:
time | location | temperature | humidity |
---|---|---|---|
2017-07-28 12:42:42.846621 01 | office | 60.1 | 50 |
ON CONFLICT DO UPDATE
example:
INSERT INTO conditions
VALUES ('2017-07-28 11:42:42.846621 00', 'office', 70.2, 50.1)
ON CONFLICT (time, location) DO UPDATE
SET humidity = excluded.temperature;
will result in:
time | location | temperature | humidity |
---|---|---|---|
2017-07-28 12:42:42.846621 01 | office | 60.1 | 70.2 |
NOTE: that we assign humidity
to excluded.temperature
- this does not really make sense in a production app, and is only used to illustrate how this works
When we use ON CONFLICT DO UPDATE
, we have access to a special table named exclude
.
This table contains the values from our insert statement that have been excluded (i.e. ignored), because other values already exist.
In our case:
excluded.temperature
is70.2
excluded.humidity
is50.1
When you do no use SET
for a column, the column keeps the old value: i.e. the temperature
will still be 60.1
after our insert statement.
When you do use SET
for a column you can assign any value you like: e.g. a constant value, an expression, or the values from the special excluded
table which contains the excluded row.