I have a table name table containing two columns foreign_table_name, and foreign_key.
Is it possible to write a SELECT query that would JOIN values of this table and the table which name is specified in the column foreign_table_name ?
For instance, if we know that all possible targetted foreign tables have a name field, I would like to know if I could write something that would:
SELECT table.foo, table.bar, foreign_table.name
FROM table
JOIN $foreign_table AS foreign_table
ON (foreign_table.id = table.foreign_key
$foreign_table = table.foreign_table);
Any solution using PlpgSQL is of course accepted.
Here's a simple content:
Table ``table``
------------------------------------------------
| foo | bar | foreign_table_name | foreign_key |
------------------------------------------------
| A | 1 | fruits | 8 |
| B | 2 | vegetable | 5 |
------------------------------------------------
Table ``fruit``
---------------
| id | name |
---------------
| 8 | apple |
---------------
Table ``vegetable``
----------------
| id | name |
----------------
| 5 | carrot |
----------------
The expected result table would be:
----------------------
| foo | bar | name |
----------------------
| A | 1 | apple |
| B | 2 | carrot |
----------------------
EDIT: I added the full table example in an attempt to be clearer.
It's usually way easier to do this sort of thing on the client side, but if you want it's possible with PL/PgSQL, e.g.
CREATE OR REPLACE FUNCTION dynamic_call(tblname text)
RETURNS TABLE (foo int, bar text, fname text)
AS $$
BEGIN
RETURN QUERY EXECUTE format('
SELECT t.foo, table.bar, f."name"
FROM mytable t
JOIN %I AS f ON (f.id = t.foreign_key);', tblname);
END;
$$ LANGUAGE plpgsql;
For more information, see the PL/PgSQL documentation.
Related
I'm struggling to find a value that might be in different tables but using UNION is a pain as there are a lot of tables.
[Different table that contains the suffixes from the TestTable_]
| ID | Name|
| -------- | -----------|
| 1 | TestTable1 |
| 2 | TestTable2 |
| 3 | TestTable3 |
| 4 | TestTable4 |
TestTable1 content:
| id | Name | q1 | a1 |
| -------- | ---------------------------------------- |
| 1 | goose | withFeather? |featherID |
| 2 | rooster| withoutFeather?|shinyfeatherID |
| 3 | rooster| age | 20 |
TestTable2 content:
| id | Name | q1 | a1 |
| -------- | ---------------------------------------------------|
| 1 | brazilian_goose | withFeather? |featherID |
| 2 | annoying_rooster | withoutFeather?|shinyfeatherID |
| 3 | annoying_rooster | no_legs? |dead |
TestTable3 content:
| id | Name | q1 | a1 |
| -------- | ---------------------------------------- |
| 1 | goose | withFeather? |featherID |
| 2 | rooster| withoutFeather?|shinyfeatherID |
| 3 | rooster| age | 15 |
Common columns: q1 and a1
Is there a way to parse through all of them to lookup for a specific value without using UNION because some of them might have different columns?
Something like: check if "q1='age'" exists in all those tables (from 1 to 50)
Select q1,*
from (something)
where q1 exists in (TestTable_*)... or something like that.
If not possible, not a problem.
You could use dynamic SQL but something I do in situations like this where I have a list of tables that I want to quickly perform the same actions on is to either use a spreadsheet to paste the list of tables into and type a query into the cell with something like #table then use the substitute function to replace it.
Alternative I just paste the list into SSMS and use SHIFT+ALT+ArrowKey to select the column and start typing stuff out.
So here is my list of tables
Then I use that key combo. As you can see my cursor has now selected all those rows.
Now I can start typing and all rows selected will get the input.
Then I just go to the other side of the table names and repeat the action
It's not a perfect solution but it's quick a quick and dirty way of doing something repetitive quickly.
If you want to find all the tables with that column name you can use information schema.
Select table_name from INFORMATION_SCHEMA.COLUMNS where COLUMN_NAME = 'q1'
Given the type of solution you are after I can offer a method that I've had to use on legacy systems.
You can query sys.columns for the name of the column(s) you need to find in N tables and join using object_id to sys.tables where type='U'. This will give you a list of table names.
From this list you can then build a working query for each table, and depending on your requirements (is this ad-hoc?) either just manually execute it yourself of build a procedure that will do it for you using sp_executesql
Eg
select t.name, c.name
into #workingtable
from sys.columns c
join sys.tables t on t.object_id=c.object_id
where c.name in .....
psudocode:
begin loop while rows exist in #working table
select top 1 row from #workingtable
set #sql=your query specific to that table and column(s)
exec(#sql) / sp_executesql / try/catch as necessary
delete row from working table
end loop
Hopefully that give ideas at least for how you might implement your requirements.
I am having a problem creating VIEWS with Snowflake that has VARIANT field which stores JSON data whose keys are dynamic and keys definition is stored in another table. So I want to create a VIEW that has dynamic columns based on the foreign key.
Here are my table looks like:
companies:
| id | name |
| -- | ---- |
| 1 | Company 1 |
| 2 | Company 2 |
invoices:
| id | invoice_number | custom_fields | company_id |
| -- | -------------- | ------------- | ---------- |
| 1 | INV-01 | {"1": "Joe", "3": true, "5": "2020-12-12"} | 1 |
| 2 | INV-01 | {"2":"Hello", "4": 1000} | 2 |
customization_fields:
| id | label | data_type | company_id |
| -- | ----- | --------- | ---------- |
| 1 | manager | text | 1 |
| 2 | reference | text | 2 |
| 3 | emailed | boolean | 1 |
| 4 | account | integer | 2 |
| 5 | due_date | date | 1 |
So I want to create a view for getting each companies invoices something like:
CREATE OR REPLACE VIEW companies_invoices AS SELECT * FROM invoices WHERE company_id = 1
which should get a result like below:
| id | invoice_number | company_id | manager | emailed | due_date |
| -- | -------------- | ---------- | ------- | ------- | -------- |
| 1 | INV-01 | 1 | Joe | true | 2020-12-12 |
So my challenge above here is I cannot make sure the keys when I write the query. If I know that I could write
SELECT
id,
invoice_number,
company_id,
custom_fields:"1" AS manager,
custom_fields:"3" AS emailed,
custom_fields:"5" AS due_date
FROM invoices
WHERE company_id = 1
These keys and labels are written in the customization_fields table, so I tried different ways and I am not able to do that.
So could anyone tell me if we can do or not? If we can please give me an example so it would really help.
You cannot do what you want to do with a view. A view has a fixed set of columns and they have specific types. Retrieving a dynamic set of columns requires some other mechanism.
If you're trying to change the number of columns or the names of the columns based on the rows in the customization_fields table, you can't do it in a view.
If you have a defined schema and just need to grab dynamic JSON properties, you may want to consider looking into Snowflake's GET function. It allows you to get any part of a JSON using a string for the path rather than using a literal path in the SQL statement. For example:
create temp table foo(v variant);
insert into foo select parse_json('{ "name":"John", "age":30, "car":null }');
-- This uses a literal path in the SQL to get to a JSON property
select v:name::string as first_name from foo;
-- This uses the GET function to get the value from a path in a string
select get(v, 'name')::string as first_name from foo;
You can replace the 'name' in the second parameter of the GET function with the value stored in the customization_fields table.
In SF, You will have to use a Stored Proc function to retrieve the dynamic set of columns
I have a table "table1" like this:
+------+--------------------+
| id | barcode | lot |
+------+-------------+------+
| 0 | ABC-123-456 | |
| 1 | ABC-123-654 | |
| 2 | ABC-789-EFG | |
| 3 | ABC-456-EFG | |
+------+-------------+------+
I have to extract the number in the center of the column "barcode", like with this request :
SELECT SUBSTR(barcode, 5, 3) AS ToExtract FROM table1;
The result:
+-----------+
| ToExtract |
+-----------+
| 123 |
| 123 |
| 789 |
| 456 |
+-----------+
And insert this into the column "lot" .
follow along the lines
UPDATE table_name
SET column1 = value1, column2 = value2, ...
WHERE condition;
i.e in your case
UPDATE table_name
SET lot = SUBSTR(barcode, 5, 3)
WHERE condition;(if any)
UPDATE table1 SET Lot = SUBSTR(barcode, 5, 3)
-- WHERE ...;
Many databases support generated (aka "virtual"/"computed" columns). This allows you to define a column as an expression. The syntax is something like this:
alter table table1 add column lot varchar(3) generated always as (SUBSTR(barcode, 5, 3))
Using a generated column has several advantages:
It is always up-to-date.
It generally does not occupy any space.
There is no overhead when creating the table (although there is overhead when querying the table).
I should note that the syntax varies a bit among databases. Some don't require the type specification. Some use just as instead of generated always as.
CREATE TABLE Table1(id INT,barcode varchar(255),lot varchar(255))
INSERT INTO Table1 VALUES (0,'ABC-123-456',NULL),(1,'ABC-123-654',NULL),(2,'ABC-789-EFG',NULL)
,(3,'ABC-456-EFG',NULL)
UPDATE a
SET a.lot = SUBSTRING(b.barcode, 5, 3)
FROM Table1 a
INNER JOIN Table1 b ON a.id=b.id
WHERE a.lot IS NULL
id | barcode | lot
-: | :---------- | :--
0 | ABC-123-456 | 123
1 | ABC-123-654 | 123
2 | ABC-789-EFG | 789
3 | ABC-456-EFG | 456
db<>fiddle here
I have a table called sentences, and a table called logs.
The sentences table looks like this:
|------------|---------------------------------------|
| id | sentence |
|------------|---------------------------------------|
| 1 | [var1] says hello! |
|------------|---------------------------------------|
| 2 | [var1] says [var2]! |
|------------|---------------------------------------|
| 3 | [var1] says [var2] and [var3]! |
|------------|---------------------------------------|
| 4 | [var4] says [var2] to [var1]! |
|------------|---------------------------------------|
The logs table looks like this:
|------------|------------------|--------------|--------------|--------------|--------------|
| id | sentenceId | var1 | var2 | var3 | var4 |
|------------|------------------|--------------|--------------|--------------|--------------|
| 1 | 1 | Sam | | | |
|------------|------------------|--------------|--------------|--------------|--------------|
| 2 | 2 | Joe | what's up | | |
|------------|------------------|--------------|--------------|--------------|--------------|
| 3 | 3 | Tim | hey | how are you | |
|------------|------------------|--------------|--------------|--------------|--------------|
| 4 | 4 | Joe | hi | | Tiffany |
|------------|------------------|--------------|--------------|--------------|--------------|
The result I am trying to get is:
|------------|-----------------------------------------|
| logs.id | sentences.sentence |
|------------|-----------------------------------------|
| 1 | [Sam] says hello! |
|------------|-----------------------------------------|
| 2 | [Joe] says [what's up]! |
|------------|-----------------------------------------|
| 3 | [Tim] says [hey] and [how are you]! |
|------------|-----------------------------------------|
| 4 | [Tiffany] says [hi] to [Joe] |
|------------|-----------------------------------------|
I'm not sure how to write the SQL query to make the database do the text substitutions for me.
I could just select everything from both tables using an inner join, and then loop through in code and do the substitutions myself. I.e.:
SELECT logs.id, sentences.sentence, logs.var1, logs.var2, logs.var3, logs.var4 FROM logs INNER JOIN sentences ON logs.sentenceId = sentences.id
And then in code:
logs.forEach(log => log.sentence.replace(/\[(.*?)\]/g, ($matchedString, $columnName) => log[$columnName] ))
But if possible, I'd like the database to do that for me so that I don't have to select more data than I need.
I would write a function to do that:
create function replace_vars(p_sentence text, p_vars jsonb)
returns text
as
$$
declare
l_rec record;
l_result text;
begin
l_result := p_sentence;
for l_rec in select * from jsonb_each_text(jsonb_strip_nulls(p_vars)) as x(var,value)
loop
l_result := replace(l_result, l_rec.var, l_rec.value);
end loop;
return l_result;
end;
$$
language plpgsql;
Then you can use it like this:
select s.id, s.sentence, replace_vars(s.sentence, to_jsonb(l)) new_sentence
from sentences s
left join logs l on l.sentenceid = s.id;
Online example
Elegance is always nice, but sometimes brute force gets it done.
with logsnn (sentenceid, var1, var2, var3,var4) as
( select sentenceid
, coalesce(var1,'')
, coalesce(var2,'')
, coalesce(var3,'')
, coalesce(var4,'')
from logs
)
select s.id
,(replace(replace(replace(replace(s.sentence
, '[var1]',l.var1)
, '[var2]',l.var2)
, '[var3]',l.var3)
, '[var4]',l.var4)
) AS sentence
from sentences s
left join logsnn l
on l.sentenceid = s.id;
If you really need the brackets on the result change the replacement settings to
'[var1]','[' || l.var1 || ']')
The answer by #JNevill is close to the same, bit I believe that one will return Null if any of var1,var2,var3, or var4 are Null. The CTE here changes Null with the empty string. Postgres does not consider the empty string the same as null.
I have one table with two columns id and data. The values in the table are as follows:
id|data|
1 |A,B |
2 |B,C |
3 |C,D |
4 |D,A |
5 |E,C |
I need number of A,B,C,D,E present in the table as follows. Please note: columns are dynamic means they are dependent upon the values in the data column from the table:
A|B|C|D|E|
2|2|3|2|1|
And I have written the following query:
SELECT id,s.data
FROM my_table t,
unnest(string_to_array(t.data, ',')) s(data);
The output is given as follows:
id|data|
1 | A |
1 | A |
1 | A |
1 | A |
1 | A |
1 | A |
1 | A |
1 | A |
Please find the query which provide exact output which you want.
select * from crosstab ('SELECT ''Total'':: text, s.data, count(*)::int
FROM my_table t, unnest(string_to_array(t.data, '','')) s(data)
group by s.data') as ct(Total text, A int, B int, C int, D int, E int)
Please create extension tablefunc (if not created).