I want that the output of the select for the column FORMATTED_JSON is null if it is empty instead of empty object, means
IDENTIFIER | FORMATTED_JSON
1 | null
This is the query:
SELECT IDENTIFIER, JSON_OBJECT('NAME' VALUE name, 'SIZE' VALUE SIZE FORMAT JSON ABSENT ON NULL) FORMATTED_JSON
FROM ABC
SELECT
IDENTIFIER
, NULLIF (JSON_OBJECT ('NAME' VALUE name, 'SIZE' VALUE SIZE ABSENT ON NULL), '{}') FORMATTED_JSON
FROM
(
VALUES
(1, 'N1', 'S1')
, (2, 'N2', NULL)
, (3, NULL, NULL)
) ABC (IDENTIFIER, NAME, SIZE)
IDENTIFIER
FORMATTED_JSON
1
{"NAME":"N1","SIZE":"S1"}
2
{"NAME":"N2"}
3
Related
I have this table
CREATE TABLE fruits
(
id SERIAL,
name VARCHAR
);
with these entries
INSERT INTO fruits(name)
VALUES('Orange');
INSERT INTO fruits(name)
VALUES('Ananas');
INSERT INTO fruits(name)
VALUES(null);
When I try to to select all rows that not equal to 'Ananas' by querying
select *
from fruits
where name <> 'Ananas'
I get these rows:
id name
-----------
1 Orange
What I would have expected was this
id name
-----------
1 Orange
3 null
How do I ensure that all rows that fulfills the condition gets selected?
Example in dbfiddle:
https://dbfiddle.uk/?rdbms=postgres_11&fiddle=a963d39df0466701b0a96b20db8461e6
Any "normal" comparison with null yields "unknown" which is treated as false in the context of the WHERE clause.
You need to use the null safe operator is distinct from:
select *
from fruits
where name is distinct from 'Ananas';
Alternatively you could convert NULL values to something different:
select *
from fruits
where coalesce(name, '') <> 'Ananas';
I have a database with three tables. Ultimately I want to JOIN the three tables and sort them by a column shared by two of the tables.
A main item table with foreign keys (product_id) to the two sub-tables:
items
CREATE TABLE items (
id INT NOT NULL,
product_id varchar(40) NOT NULL,
type CHAR NOT NULL
);
and then a table corresponding to each typeA and typeB. They have differing columns, but for the sake of this exercise I'm only including the columns they have in common:
CREATE TABLE products_a (
id varchar(40) NOT NULL,
name varchar(40) NOT NULL,
price INT NOT NULL
);
CREATE TABLE products_b (
id varchar(40) NOT NULL,
name varchar(40) NOT NULL,
price INT NOT NULL
);
Some example rows:
INSERT INTO items VALUES
( 1, 'abc', 'a' ),
( 2, 'def', 'b' ),
( 3, 'ghi', 'a' ),
( 4, 'jkl', 'b' );
INSERT INTO products_a VALUES
( 'abc', 'product 1', 10 ),
( 'ghi', 'product 2', 50 );
INSERT INTO products_b VALUES
( 'def', 'product 3', 20 ),
( 'jkl', 'product 4', 100 );
I have a JOIN working, but my sorting is not interpolating the rows as I would expect.
Query:
SELECT
items.id AS item_id,
products_a.name AS product_a_name,
products_a.price AS product_a_price,
products_b.name AS product_b_name,
products_b.price AS product_b_price
FROM items
FULL JOIN products_a ON items.product_id = products_a.id
FULL JOIN products_b ON items.product_id = products_b.id
ORDER BY 3, 5 ASC;
Actual result:
item_id
product_a_name
product_a_price
product_b_name
product_b_price
1
product 1
10
NULL
NULL
3
product 2
50
NULL
NULL
2
NULL
NULL
product 3
20
4
NULL
NULL
product 4
100
Desired result:
item_id
product_a_name
product_a_price
product_b_name
product_b_price
1
product 1
10
NULL
NULL
2
NULL
NULL
product 3
20
3
product 2
50
NULL
NULL
4
NULL
NULL
product 4
100
I realize this is a weird table setup, but simplified this way looks more contrived than it is. Ultimately the sorting matches the real use case, though, and changing the DB schema is not an option. I feel like I am missing something simple here, just sorting by either one column or another. Any help is appreciated.
Use COALESCE in the ORDER BY clause to always sort by the first non NULL price:
SELECT
items.id AS item_id,
products_a.name AS product_a_name,
products_a.price AS product_a_price,
products_b.name AS product_b_name,
products_b.price AS product_b_price
FROM items
FULL JOIN products_a ON items.product_id = products_a.id
FULL JOIN products_b ON items.product_id = products_b.id
ORDER BY
COALESCE(3, 5);
Given the table
ID PERSON_ID PLAN EMPLOYER_ID TERMINATION_DATE
1 123 ABC 321 2020-01-01
2 123 DEF 321 (null)
3 123 ABC 321 (null)
4 123 ABC 321 (null)
I want to exclude the 4th entry. (The 3rd entry shows the person was re-hired and therefore is a new relationship. I'm only showing relevant fields)
My first attempt was to simply create a unique index over PERSON_ID / PLAN / EMPLOYER_ID / TERMINATION_DATE, thinking that DB2 for IBMi considered nulls equal in a unique index. I was evidently wrong...
Is there a way to enforce uniqueness over these columns, or,
is there a better way to approach the value of termination date? (null is not technically correct; I'm thinking of it as more true/false, but the business logic needs a date)
Edit
According to the docs for 7.3:
UNIQUE
Prevents the table from containing two or more rows with the same value of the index key. When UNIQUE is used, all null values for a column are considered equal. For example, if the key is a single column that can contain null values, that column can contain only one null value. The constraint is enforced when rows of the table are updated or new rows are inserted.
The constraint is also checked during the execution of the CREATE INDEX statement. If the table already contains rows with duplicate key values, the index is not created.
UNIQUE WHERE NOT NULL
Prevents the table from containing two or more rows with the same value of the index key, where all null values for a column are not considered equal. Multiple null values in a column are allowed. Otherwise, this is identical to UNIQUE.
So, the behavior I'm seeing looks more like UNIQUE WHERE NOT NULL. When I generate SQL for this table, I see
ADD CONSTRAINT TERMEMPPLANSSN
UNIQUE( TERMINATION_DATE , EMPLOYERID , PLAN_CODE , SSN ) ;
(note this is showing the real field names, not the ones I used in my example)
Edit 2
Bottom line, Constraint !== Index. When I went back and created an actual index, I got the desired behavior.
CREATE TABLE PERSON
(
ID INT NOT NULL
, PERSON_ID INT NOT NULL
, PLAN CHAR(3) NOT NULL
, EMPLOYER_ID INT
, TERMINATION_DATE DATE
);
INSERT INTO PERSON (ID, PERSON_ID, PLAN, EMPLOYER_ID, TERMINATION_DATE)
VALUES
(1, 123, 'ABC', 321, DATE('2020-01-01'))
, (2, 123, 'DEF', 321, CAST(NULL AS DATE))
, (3, 123, 'ABC', 321, CAST(NULL AS DATE))
WITH NC;
--- To not allow: ---
INSERT INTO PERSON (ID, PERSON_ID, PLAN, EMPLOYER_ID, TERMINATION_DATE) VALUES
(4, 123, 'ABC', 321, CAST(NULL AS DATE))
or
(4, 123, 'ABC', 321, DATE('2020-01-01'))
You may:
CREATE UNIQUE INDEX PERSON_U1 ON PERSON
(PERSON_ID, PLAN, EMPLOYER_ID, TERMINATION_DATE);
--- To not allow: ---
INSERT INTO PERSON (ID, PERSON_ID, PLAN, EMPLOYER_ID, TERMINATION_DATE) VALUES
(4, 123, 'ABC', 321, DATE('2020-01-01'))
but allow multiple:
(X, 123, 'ABC', 321, CAST(NULL AS DATE))
(Y, 123, 'ABC', 321, CAST(NULL AS DATE))
...
You may:
CREATE UNIQUE WHERE NOT NULL INDEX PERSON_U2 ON PERSON
(PERSON_ID, PLAN, EMPLOYER_ID, TERMINATION_DATE);
I am using PostgreSQL 10.4 and have 2 tables:
person:
CREATE TABLE person (
nationality character varying(100),
name character varying(100),
age integer
);
country:
CREATE TABLE country (
demonym character varying(50),
name character varying(50)
);
This is the query that I am trying to run:
select "c"."name",
(SELECT row_to_json(r) FROM (
SELECT
COALESCE(sum(CASE WHEN p."nationality"='finn' THEN 1 ELSE 0 END),0) as "1",
COALESCE(sum(CASE WHEN p."nationality"='spanish' THEN 1 ELSE 0 END),0) as "2"
FROM "person" as p
WHERE "p"."nationality"="c"."demonym"
) as r) as "nationalitiesCount"
from "country" as c
WHERE 'nationalitiesCount'::json->'1' > 10
This yields an error:
ERROR: invalid input syntax for type json
LINE 11: WHERE 'nationalitiesCount'::json->'1' > 10
DETAIL: Token "nationalitiesCount" is invalid.
CONTEXT: JSON data, line 1: nationalitiesCount
The second line has the first ' highlighted as the code which causes the error to appear.
Question: How could the error be rectified?
The first issue is that references to columns should not be in single quotes, though they can be / sometimes have to be in double quotes, which is why it doesn't like 'nationalitiesCount'::json->'1'. The second is that the column name nationalitiesCount is defined in the SELECT part of the query and can't be referenced in the WHERE clause of the query where it's defined, so you can move your query into a subquery so you can reference it outside of the subquery.
select *
from (select "c"."name",
(SELECT row_to_json(r)
FROM (
SELECT
COALESCE(sum(CASE WHEN p."nationality"='finn' THEN 1 ELSE 0 END),0) as "1",
COALESCE(sum(CASE WHEN p."nationality"='spanish' THEN 1 ELSE 0 END),0) as "2"
FROM "person" as p
WHERE "p"."nationality"="c"."demonym"
) as r) as "nationalitiesCount"
from "country" as c
) t
WHERE (t."nationalitiesCount"->>'1')::integer > 10
I have to build a procedure that returns a table at the end, which contains a list of fields where specific substances were applied. I need to return one row for each field and the applied substance.
This works great for all fields where something was actually applied, but I also need to display the same amount of rows for those fields, were nothing was applied.
At the moment I get a table like this:
Field 1 | Substance 1 | 12345 kg
Field 1 | Substance 2 | 23423 kg
Field 2 | Substance 1 | 23236 kg
Field 2 | Substance 2 | 12312 kg
Field 3 | NULL | NULL
I know that I could swap the NULL value with at least one Substance by making a Case-Condition, but I need two rows (one for Substance 1 and one for Substance 2) containing the names of each substance.
Is there any way to achieve this?
Or maybe you have something like this:
CREATE TABLE Fields (
FieldID INT PRIMARY KEY,
FieldName VARCHAR(50) NOT NULL UNIQUE,
)
INSERT INTO dbo.Fields (FieldID, FieldName) VALUES
(1, 'Field 1'),
(2, 'Field 2'),
(3, 'Field 3')
CREATE TABLE dbo.Substances (
SubstanceID INT PRIMARY KEY,
Substance VARCHAR(50) NOT NULL UNIQUE
)
INSERT INTO dbo.Substances (SubstanceID, Substance) VALUES
(1, 'Substance 1'),
(2, 'Substance 2')
CREATE TABLE AppliedSubstances (
FieldID INT NOT NULL REFERENCES dbo.Fields,
SubstanceID INT NOT NULL REFERENCES dbo.Substances,
Quantity INT NOT NULL
)
INSERT INTO dbo.AppliedSubstances (FieldID, SubstanceID, Quantity) VALUES
(1, 1, 12345),
(1, 2, 23423),
(2, 1, 23236),
(2, 2, 12312)
Then you can use the following query:
SELECT f.FieldName, s.Substance, a.Quantity
FROM dbo.AppliedSubstances a
INNER JOIN dbo.Fields f ON f.FieldID = a.FieldID
INNER JOIN dbo.Substances s ON s.SubstanceID = a.SubstanceID
UNION ALL
SELECT f.FieldName, s.Substance, NULL AS Quantity
FROM dbo.Fields f
CROSS JOIN dbo.Substances s
WHERE NOT EXISTS (
SELECT * FROM dbo.AppliedSubstances a
WHERE a.FieldID=f.FieldID AND a.SubstanceID=s.SubstanceID
)
Or a shorter stranger version (with a different meaning if you have some substances that were applied only for some fields):
SELECT f.FieldName, s.Substance, a.Quantity
FROM dbo.AppliedSubstances a
RIGHT JOIN dbo.Fields f ON f.FieldID = a.FieldID
INNER JOIN dbo.Substances s ON s.SubstanceID = ISNULL(a.SubstanceID,s.SubstanceID)
I'm not sure if I understand your question correctly, but try this:
CREATE TABLE SourceData (
FieldName VARCHAR(50),
Substance VARCHAR(50),
Quantity INT
)
INSERT INTO dbo.SourceData (FieldName, Substance, Quantity) VALUES
('Field 1', 'Substance 1', 12345),
('Field 1', 'Substance 2', 23423),
('Field 2', 'Substance 1', 23236),
('Field 2', 'Substance 2', 12312),
('Field 3', NULL, NULL)
SELECT FieldName, Substance, Quantity
FROM dbo.SourceData WHERE Substance IS NOT NULL
UNION ALL
SELECT s1.FieldName, x.Substance, NULL AS Quantity
FROM dbo.SourceData s1 CROSS JOIN (
SELECT DISTINCT s2.Substance
FROM dbo.SourceData s2
WHERE s2.Substance IS NOT NULL
) x
WHERE s1.Substance IS NULL