How would you create a trigger that uses the values of the row being inserted to be calculated first so that a value being inserted gets transformed?
Let's say I have this table labor_rates,
+---------------+-----------------+--------------+------------+
| labor_rate_id | rate_per_minute | unit_minutes | created_at |
+---------------+-----------------+--------------+------------+
| bigint | numeric | numeric | timestamp |
+---------------+-----------------+--------------+------------+
Each time a new record is created, I need that the rate is calculated as rate/unit (the smallest unit here is a minute).
So example, when inserting a new record:
INSERT INTO labor_rates(rate, unit)
VALUES (60, 480);
It would create a new record with these values:
+---------------+-----------------+--------------+----------------------------+
| labor_rate_id | rate_per_minute | unit_minutes | created_at |
+---------------+-----------------+--------------+----------------------------+
| 1000000 | 1.1979 | 60 | 2017-03-16 01:59:47.208111 |
+---------------+-----------------+--------------+----------------------------+
One could argue that this should be left as a calculated field instead of storing the calculated value. But in this case, it would be best if the calculated value is stored.
I am fairly new to triggers so any help would be much appreciated.
Related
I have some data imported from a GeoPackage by using the ogr2ogr tool. I assume the import operation goes without any glitches since ST_IsValidReason() returns Valid Geometry for the imported multi-polygons (the geom column).
nzstat=# \d sa2_2020
Table "public.sa2_2020"
Column | Type | Collation | Nullable | Default
-----------------+-----------------------------+-----------+----------+---------------------------------------
gid | integer | | not null | nextval('sa2_2020_gid_seq'::regclass)
sa22018_v1_00 | character varying | | |
sa22018_v1_name | character varying | | |
land_area_sq_km | double precision | | |
area_sq_km | double precision | | |
shape_length | double precision | | |
geom | geometry(MultiPolygon,2193) | | |
Indexes:
"sa2_2020_pkey" PRIMARY KEY, btree (gid)
"sa2_2020_geom_geom_idx" gist (geom)
nzstat=# select ST_IsValidReason(geom) from sa2_2020 where gid=4;
st_isvalidreason
------------------
Valid Geometry
(1 row)
nzstat=# select ST_IsValidReason(ST_SetSRID(ST_MakePoint(174.77632, -41.28671), 2193));
st_isvalidreason
------------------
Valid Geometry
(1 row)
nzstat=# select sa22018_v1_name from sa2_2020 where ST_Within(ST_SetSRID(ST_MakePoint(174.82726, -41.16671), 2193), geom);
sa22018_v1_name
-----------------
(0 rows)
nzstat=#
The coordinates I use for ST_MakePoint() are from another database which gives the x and y values in NZGD2000 coordinate system (SRID = 2193)
full_address_ascii | gd2000_xcoord | gd2000_ycoord
-------------------------------------------------+---------------+---------------
1 Willis Street, Wellington Central, Wellington | 174.77632 | -41.28671
The coordinate should be in one of the multi-polygons but my query returns no results. Is there anything I am missing here?
I use PostGIS 3.2 with PostgeSQL 13.5.
Thanks
EPSG:2193 has coordinates in metres so it is unlikely that your values (174.82726, -41.16671) are in that projection, it is much more likely that they are in degrees (WGS84, EPGS:4326). So you need to transform your point to compare them to polygons in EPSG:2193, thus your SQL should be something like:
select sa22018_v1_name from sa2_2020 where ST_Within(ST_TRANSFORM(ST_MakePoint(174.82726, -41.16671), 2193), geom);
ST_SetSRID only changes the metadata of the point (setting the CRS), to actually change the values of a point's coordinates you need to reproject the point (transform it from one projection to another) and so must use ST_Transform.
Suppose there is a table with data:
+----+-------+
| id | value |
+----+-------+
| 1 | 0 |
| 2 | 0 |
+----+-------+
I need to do a bulk update. And use COPY FROM STDIN for fast insert to temp table without constraints and so it can contains duplicate values in id column
Temp table to update from:
+----+-------+
| id | value |
+----+-------+
| 1 | 1 |
| 2 | 1 |
| 1 | 2 |
| 2 | 2 |
+----+-------+
If I simply run a query like with:
UPDATE test target SET value = source.value FROM tmp_test source WHERE target.id = source.id;
I got wrong results:
+----+-------+
| id | value |
+----+-------+
| 1 | 1 |
| 2 | 1 |
+----+-------+
I need the target table to contain the values that appeared last in the temporary table.
What is the most effective way to do this, given that the target table may contain millions of records, and the temporary table may contain tens of thousands?**
Assuming you want to take the value from the row that was inserted last into the temp table, physically, you can (ab-)use the system column ctid, signifying the physical location:
UPDATE test AS target
SET value = source.value
FROM (
SELECT DISTINCT ON (id)
id, value
FROM tmp_test
ORDER BY id, ctid DESC
) source
WHERE target.id = source.id
AND target.value <> source.value; -- skip empty updates
About DISTINCT ON:
Select first row in each GROUP BY group?
This builds on a implementation detail, and is not backed up by the SQL standard. If some insert method should not write rows in sequence (like future "parallel" INSERT), it breaks. Currently, it should work. About ctid:
How do I decompose ctid into page and row numbers?
If you want a safe way, you need to add some user column to signify the order of rows, like a serial column. But do your really care? Your tiebreaker seems rather arbitrary. See:
Temporary sequence within a SELECT
AND target.value <> source.value
skips empty updates - assuming both columns are NOT NULL. Else, use:
AND target.value IS DISTINCT FROM source.value
See:
How do I (or can I) SELECT DISTINCT on multiple columns?
I will be very grateful for your advice regarding the following issue.
Given:
PostgreSQL database
Initial (basic) query
select day, Value_1, Value_2, Value_3
from table
where day=current_date
which returns a row with following columns
Day | Value_1(int) | Value_2(int) | Value 3 (int)
2019-11-14 | 10 | 10 | 14
It is needed to create a view with this starting information and add a new row every day based on the outcome of initial query executed at 22:00.
The expected outcome tomorrow at 22:01 will be
Day | Value_1 | Value_2 | Value_3
2019-11-14 | 10 | 10 | 14
2019-11-15 | N | M | P
Many thanks in advance for your time and support.
Why does this query returns a record?:
db2=> select * FROM series WHERE start <= '882001010000' AND "end" >= '882001010000' ORDER BY timestamp DESC LIMIT 1;
id | timestamp | start | end |
-------+---------------------+----------+-----------
23443 | 2016-12-23 17:10:05 | 88160000 | 88209999 |
or with BETWEEN:
db2=> select * FROM series WHERE '882001010000' BETWEEN start AND "end" ORDER BY timestamp DESC LIMIT 1;
id | timestamp | start | end |
-------+---------------------+----------+-----------
23443 | 2016-12-23 17:10:05 | 88160000 | 88209999 |
start and end are TEXT columns.
They are returning records because you are doing the comparisons as strings not as numbers.
Hence: '8' is between '7000000' and '9000', because the comparisons are one character at a time.
If you want numeric comparisons, you can cast the values to numbers. Or, better yet, represent the values as numerics. Postgres has the nice capability of very large precisions.
Here is my table in the database :
id | account_name | account_number | account_type | address | email | ifsc_code | is_default_account | phone_num | User
-----+--------------+----------------+--------------+---------+------------------------------+-----------+--------------------+-------------+----------
201 | helloi32irn | 55265766432454 | Savings | | mypal.appa99721989#gmail.com | 5545 | f | 98654567876 | abc
195 | hello | 55265766435523 | Savings | | mypal.1989#gmail.com | 5545 | t | 98654567876 | axyz
203 | what | 01010101010101 | Current | | guillaume#sample.com | 6123 | f | 09099990 | abc
On form submission in the view, which only posts a single parameter which in my case is name= "activate" which corresponds to the column "is_default_account" in the table.
I want to change the value of "is_default_account" from "t" to "f". For example here in the table, for account_name "hello" it is "t". And i want to deactivate it, i.e make it "f" and activate any of the other that has been sent trough the form
This will update your table and make account 'what' default (assuming that is_default_account is BOOLEAN field):
UPDATE table
SET is_default_account = (account_name = 'what')
You may want limit updates if table is more than just few rows you listed, like this:
UPDATE table
SET is_default_account = (account_name = 'what')
WHERE is_default_account != (account_name = 'what')
AND <limit updates by some other criteria like user name>
I think to accomplish what you want to do you should send at least two values from the form. One for the id of the account you want to update and the other for the action (activate here). You can also just send the id and have it toggle. There are many ways to do this but I can't figure out exactly what you are trying to do and whether you want SQL or Playframework code. Without limiting your update in somewhere (like id) you can't precisely control what specific rows get updated. Please clarify your question and add some more code if you want help on the playframework side, which I would think you do.