I want to pass column name as a parameter. Here I have written a query to select the column 'user_id' from table users, but it returns user_id as text.
EXECUTE format('SELECT $1 FROM users
WHERE name=''name''')
USING 'user_id';
How can I do this?
Can you not use Dynamic SQL to get this result? something like:
EXECUTE 'SELECT '|| get_columns()|| ' FROM table_name'
According to documentation...
Note that parameter symbols can only be used for data values — if you
want to use dynamically determined table or column names, you must
insert them into the command string textually. For example, if the
preceding query needed to be done against a dynamically selected table...
So you need something like this
EXECUTE 'SELECT '
|| quote_ident(p_column)
|| ' FROM users '
|| ' WHERE name = $1'
INTO v_result
USING name;
p_column is the column name received as a parameter in your function.
v_result is a variable for storing the result. This INTO part can be discarded if you don't care about the result.
name is the value supplied to the where condition. Must be somewhere in your function or get as a parameter too.
Related
I have tables that contain the same type of data for every year, but the data gathered varies slightly in that they may not have the same fields.
d_abc_2016
d_def_2016
d_ghi_2016
d_jkl_2016
There are certain constants for each table: company_id, employee_id, salary.
However, each one might or might not have these fields that are used to calculate total incentives: bonus, commission, cash_incentives. There are a lot more, but just using these as a examples. All numeric
I should note at this point, users only have the ability to run SELECT statements.
What I would like to be able to do is this:
Give the user the ability to call in SELECT and specify their own fields in addition to the call
Pass the table name being used into the function to use in conditional logic to determine how the query string should be constructed for the eventual total_incentives calculation in addition to passing the whole table so a ton of arguments don't have to be passed into the function
Basically this:
SELECT employee_id, salary, total_incentives(t, 'd_abc_2016')
FROM d_abc_2016 t;
So the function being called will calculate total_incentives which is numeric for that employee_id and also show their salary. But the user might choose to add other fields to look at.
For the function, because the fields used in the total_incentives function will vary from table to table, I need to create logic to construct the query string dynamically.
CREATE OR REPLACE FUNCTION total_incentives(ANYELEMENT, t text)
RETURNS numeric AS
$$
DECLARE
-- table name lower case in case user typed wrong
tbl varchar(255) := lower($2;
-- parse out the table code to use in conditional logic
tbl_code varchar(255) := split_part(survey, '_', 2);
-- the starting point if the query string
base_calc varchar(255) := 'salary + '
-- query string
query_string varchar(255);
-- have to declare this to put computation INTO
total_incentives_calc numeric;
BEGIN
IF tbl_code = 'abc' THEN
query_string := base_calc || 'bonus';
ELSIF tbl_code = 'def' THEN
query_string := base_calc || 'bonus + commission';
ELSIF tbl_code = 'ghi' THEN
-- etc...
END IF;
EXECUTE format('SELECT $1 FROM %I', tbl)
INTO total_incentives_calc
USING query_string;
RETURN total_incentives_calc;
END;
$$
LANGUAGE plpgsql;
This results in an:
ERROR: invalid input syntax for type numeric: "salary + bonus"
CONTEXT: PL/pgSQL function total_incentives(anyelement,text) line 16 at EXECUTE
Since it should be returning a set of numeric values. Change it to the following:
CREATE OR REPLACE FUNCTION total_incentives(ANYELEMENT, t text)
RETURNS SETOF numeric AS
$$
...
RETURN;
Get the same error.
Figure well, maybe it is a table it is trying to return.
CREATE OR REPLACE FUNCTION total_incentives(ANYELEMENT, t text)
RETURNS TABLE(tot_inc numeric) AS
$$
...
Get the same error.
Really, any variation produces that result. So really not sure how to get this to work.
Look at RESULT QUERY, RESULT NEXT, or RESULT QUERY EXECUTE.
https://www.postgresql.org/docs/9.6/static/plpgsql-control-structures.html
RESULT QUERY won't work because it takes a hard coded query from what I can tell, which won't take in variables.
RESULT NEXT iterates through each record, which I don't think will be suitable for my needs and seems like it will be really slow... and it takes a hard coded query from what I can tell.
RESULT QUERY EXECUTE sounds promising.
-- EXECUTE format('SELECT $1 FROM %I', tbl)
-- INTO total_incentives_calc
-- USING query_string;
RETURN QUERY
EXECUTE format('SELECT $1 FROM %I', tbl)
USING query_string;
And get:
ERROR: structure of query does not match function result type
DETAIL: Returned type character varying does not match expected type numeric in column 1.
CONTEXT: PL/pgSQL function total_incentives(anyelement,text) line 20 at RETURN QUERY
It should be returning numeric.
Lastly, I can get this to work, but it won't be DRY. I'd rather not make a bunch of separate functions for each table with duplicative code. Most of the working examples I have seen have the whole query in the function and are called like such:
SELECT total_incentives(d_abc_2016, 'd_abc_2016');
So any additional columns would have to be specified in the function as:
EXECUTE format('SELECT employee_id...)
Given the users will only be able to run SELECT in query this really isn't an option. They need to specify any additional columns they want to see inside a query.
I've posted a similar question but was told it was unclear, so hopefully this lengthier version will more clearly explain what I am trying to do.
The column names and tables names should not be used as query parameters passed by USING clause.
Probably lines:
RETURN QUERY
EXECUTE format('SELECT $1 FROM %I', tbl)
USING query_string;
should be:
RETURN QUERY
EXECUTE format('SELECT %s FROM %I', query_string, tbl);
This case is example why too DRY principle is sometimes problematic. If you write it directly, then your code will be simpler, cleaner and probably shorter.
Dynamic SQL is one from last solution - not first. Use dynamic SQL only when your code will be significantly shorter with dynamic sql than without dynamic SQL.
I have column names stored in variable colls, next I execute code:
DO $$
DECLARE
v_name text := quote_ident('colls');
BEGIN
EXECUTE 'insert into table1 select '|| colls ||' from table2 ';
-- EXECUTE 'insert into table1 select '|| v_name ||' from table2 ';
END$$;
I have got error: column "colls" does not exist. Program used colls as name not as variable. What am I doing wrong?
I have found similar example in documentation:
https://www.postgresql.org/docs/8.1/static/plpgsql-statements.html#PLPGSQL-STATEMENTS-EXECUTING-DYN
I have column names stored in variable colls
No, you don't. You have a variable v_name - which holds a single word: 'colls'. About variables in SQL:
User defined variables in PostgreSQL
Read the chapters Identifiers and Key Words and Constants in the manual.
And if you had multiple column names in a single variable, you could not use quote_ident() like that. It would escape the whole string as a single identifier.
I guess the basic misunderstanding is this: 'colls' is a string constant, not a variable. There are no other variables in a DO statement than the ones you declare in the DECLARE section. You might be looking for a function that takes a variable number of column names as parameter(s) ...
CREATE OR REPLACE FUNCTION f_insert_these_columns(VARIADIC _cols text[])
RETURNS void AS
$func$
BEGIN
EXECUTE (
SELECT 'INSERT INTO table1 SELECT '
|| string_agg(quote_ident(col), ', ')
|| ' FROM table2'
FROM unnest(_cols) col
);
END
$func$ LANGUAGE plpgsql;
Call:
SELECT f_insert_these_columns('abd', 'NeW Deal'); -- column names case sensitive!
SELECT f_insert_these_columns(VARIADIC '{abd, NeW Deal}'); -- column names case sensitive!
Note how I unnest the array of column names and escape them one by one.
A VARIADIC parameter should be perfect for your use case. You can either pass a list of column names or an array.
Either way, be vary of SQL injection.
Related, with more explanation:
Pass multiple values in single parameter
Table name as a PostgreSQL function parameter
I'm executing an UPDATE statement in a TADOQuery and I'm using parameters for a few things. Initially, this was working just fine, but I added another parameter for the table name and field name, and now it's breaking.
The code looks like this:
Q.SQL.Text:= 'update :tablename set :fieldname = :newid where :fieldname = :oldid';
Q.Parameters.ParamValues['tablename']:= TableName;
Q.Parameters.ParamValues['fieldname']:= FieldName;
Q.Parameters.ParamValues['oldid']:= OldID;
Q.Parameters.ParamValues['newid']:= NewID;
And the error I get:
I'm assuming this is because I'm using this field name twice. I can overcome this by using another unique field name for the second time it's used, however I still have another error:
How do I use the parameters to specify the table and field to update?
Query parameters aren't designed to parameterize table names.
What you can do is use placeholders for the table name(s) in your SQL, and then use the Format function to replace those with the table name(s), and then use parameters for the other values as usual. This is still relatively safe from SQL injection (the malevolent person would have to know the precise table names, the specific SQL statement being used, and values to provide for parameters).
const
QryText = 'update %s set :fieldname = :newid where :fieldname = :oldid';
begin
Q.SQL.Text := Format(QryText, [TableName]);
Q.Parameters.ParamValues['fieldname'] := FieldName;
Q.Parameters.ParamValues['oldid'] := OldID;
Q.Parameters.ParamValues['newid'] := NewID;
...
end;
I want to write a simple query to select a number of columns in PostgreSQL. However, I keep getting errors - I tried a few options but they did not work for me. At the moment I am getting the following error:
org.postgresql.util.PSQLException: ERROR: syntax error at or near
"column"
To get the columns with values I try the followig:
select * from weather_data where column like '%2010%'
Any ideas?
column is a reserved word. You cannot use it as identifier unless you double-quote it. Like: "column".
Doesn't mean you should, though. Just don't use reserved words as identifiers. Ever.
To ...
select a list of columns with 2010 in their name:
.. you can use this function to build the SQL command dynamically from the system catalog table pg_attribute:
CREATE OR REPLACE FUNCTION f_build_select(_tbl regclass, _pattern text)
RETURNS text AS
$func$
SELECT format('SELECT %s FROM %s'
, string_agg(quote_ident(attname), ', ')
, $1)
FROM pg_attribute
WHERE attrelid = $1
AND attname LIKE ('%' || $2 || '%')
AND NOT attisdropped -- no dropped (dead) columns
AND attnum > 0; -- no system columns
$func$ LANGUAGE sql;
Call:
SELECT f_build_select('weather_data', '2010');
Returns something like:
SELECT foo2010, bar2010_id, FROM weather_data;
You cannot make this fully dynamic, because the return type is unknown until we actually build the query.
This will get you the list of columns in a specific table (you can optionally add schema if needed):
SELECT column_name
FROM information_schema.columns
WHERE table_name = 'yourtable'
and column_name like '%2010%'
SQL Fiddle Demo
You can then use that query to create a dynamic sql statement to return your results.
Attempts to use dynamic structures like this usually indicate that you should be using data formats like hstore, json, xml, etc that are amenible to dynamic access.
You can get a dynamic column list by creating the SQL on the fly in your application. You can query the INFORMATION_SCHEMA to get information about the columns of a table and build the query.
It's possible to do this in PL/PgSQL and run the generated query with EXECUTE but you'll find it somewhat difficult to work with the result RECORD, as you must get and decode composite tuples, you can't expand the result set into a normal column list. Observe:
craig=> CREATE OR REPLACE FUNCTION retrecset() returns setof record as $$
values (1,2,3,4), (10,11,12,13);
$$ language sql;
craig=> select retrecset();
retrecset
---------------
(1,2,3,4)
(10,11,12,13)
(2 rows)
craig=> select * from retrecset();
ERROR: a column definition list is required for functions returning "record"
craig=> select (r).* FROM (select retrecset()) AS x(r);
ERROR: record type has not been registered
About all you can do is get the raw record and decode it in the client. You can't index into it from SQL, you can't convert it to anything else, etc. Most client APIs don't provide facilities for parsing the text representations of anonymous records so you'll likely have to write this yourself.
So: you can return dynamic records from PL/PgSQL without knowing their result type, it's just not particularly useful and it is a pain to deal with on the client side. You really want to just use the client to generate queries in the first place.
You can't search all columns like that. You have to specify a specific column.
For example,
select * from weather_data where weather_date like '%2010%'
or better yet if it is a date, specify a date range:
select * from weather_data where weather_date between '2010-01-01' and '2010-12-31'
Found this here :
SELECT 'SELECT ' || array_to_string(ARRAY(SELECT 'o' || '.' || c.column_name
FROM information_schema.columns As c
WHERE table_name = 'officepark'
AND c.column_name NOT IN('officeparkid', 'contractor')
), ',') || ' FROM officepark As o' As sqlstmt
The result is a SQL SELECT query you just have to execute further.
It fits my needs since I pipe the result in the shell like this :
psql -U myUser -d myDB -t -c "SELECT...As sqlstm" | psql -U myUser -d myDB
That returns me the formatted output, but it only works in the shell.
Hope this helps someone someday.
I am writing some Pl/SQl in which I used an array Variable of Length 5.
Then I stored all the Column name of another table into the above declared array.
Now I am looking for a solution by which I can use the Array element in select Query to fetch the data from another table which exactly has the column name.
Like
arr(1):='Name'
arr(2):='Course'
The Query in Pl/Sql should be something like this (for reference only)
select arr(1) from Mttable;
==== This generates error when I write the Query in this way
Note- All work should be done in Pl/SQL on Oracle 10g
Please Help.
You can build up a query in a string and execute the string. My PL/SQL is rusty, but something like:
begin
query := 'select ' || arr(1) || ' from Mttable';
execute immediate query;
end;