I'm trying to insert a alphanumeric value in a table:
INSERT INTO solution (solution, nextsolution) VALUES
('9Na_(2)SO_(4)', NULL), ('2Ni(OH)_(3)', (SELECT id FROM solution WHERE solution='9Na_(2)SO_(4)' & nextsolution=null));
solution is of type text and nextsolution is an integer. Unfortunately postgresql doesn't allow me to do the WHERE clause. It gives me the error:
ERROR: invalid input syntax for integer: "9Na_(2)SO_(4)"
LINE 9: ...OH)_(3)', (SELECT id FROM solution WHERE solution='9Na_(2)SO...
How can I solve this?
The issue is that the statement in the where clause: '9Na_(2)SO_(4)' & nextsolution=null tries to do a bitwise and (&) operation on the string and this won't work (and probably isn't what you want anyway).
Looking at your query I think what you want is to first insert the value '9Na_(2)SO_(4)' and then the value '2Ni(OH)_(3)' with the id of the previous inserted row.
You need to do this as two statements and use a different syntax. This should do what you want:
INSERT INTO solution (solution, nextsolution) VALUES (
'9Na_(2)SO_(4)',
NULL
);
INSERT INTO solution (solution, nextsolution) VALUES (
'2Ni(OH)_(3)',
(SELECT id FROM solution WHERE solution='9Na_(2)SO_(4)' and nextsolution is null)
);
You need to use AND instead of & to join your WHERE clause - an ampersand (&) is used for bitwise operations.
Related
I have field that has up to 9 comma separated values each of which have a string value and a numeric value separated by colon. After parsing them all some of the values between 0 and 1 are being set to an integer rather than a numeric as cast. The problem is obviously related to data type but I am unsure what is causing it or how to fix it. The problem only exists in the case statement, the split_part function seems to be working perfect.
Things I have tried:
nvl(split_part(one,':',2),0) = COALESCE types text and integer cannot be matched
nvl(split_part(one,':',2)::numeric,0) => Invalid input syntax for type numeric
numerous other cast/convert variations
(CASE WHEN split_part(one,':',2) = '' THEN 0::numeric ELSE split_part(one,':',2)::numeric END)::numeric => runs but get int value of 0
When using the split_part function outside of case statement it does work correctly. However, I need the result to be zero for null values.
split_part(one,':',2) => 0.02068278096187390979 (expected result)
When running the code above I get zero but expect 0.02068278096187390979
Field "one" has the following value 'xyz: 0.02068278096187390979' before the split_part function.
EXAMPLE:
create table test(one varchar);
insert into test values('XYZ: 0.50000000000000000000')
select
one ,split_part(one,':',2) as correct_value_for_those_that_are_not_null ,
case
when split_part(one,':',2) = '' then null
else split_part(one,':',2)::numeric
end::numeric as this_one_is_the_problem
from test
However, I need the result to be zero for null values.
Your example does not deal with NULL values at all, though. Only addressing the empty string ('').
To replace either with 0 reliably, efficiently and without casting issues:
SELECT part1, CASE WHEN part2 <> '' THEN part2::numeric ELSE numeric '0' END AS part2
FROM (
SELECT split_part(one, ':', 1) AS part1
, split_part(one, ':', 2) AS part2
FROM test
) sub;
See:
Best way to check for "empty or null value"
Also note that all SQL CASE branches must agree on a common data type. There have been minor adjustments in the logic that determines the resulting type in the past, so the version of Postgres may play a role in corner cases. Don't recall the details now.
nvl()is not a Postgres function. You probably meant COALESCE. The manual:
This SQL-standard function provides capabilities similar to NVL and IFNULL, which are used in some other database systems.
original query looks like this :
UPDATE reponse_question_finale t1, reponse_question_finale t2 SET
t1.nb_question_repondu = (9-(ISNULL(t1.valeur_question_4)+ISNULL(t1.valeur_question_6)+ISNULL(t1.valeur_question_7)+ISNULL(t1.valeur_question_9))) WHERE t1.APPLICATION = t2.APPLICATION;
I know you cannot update 2 tables in a single query so i tried this :
UPDATE reponse_question_finale t1
SET nb_question_repondu = (9-(COALESCE(t1.valeur_question_4,'')::int+COALESCE(t1.valeur_question_6,'')::int+COALESCE(t1.valeur_question_7)::int+COALESCE(t1.valeur_question_9,'')::int))
WHERE t1.APPLICATION = t1.APPLICATION;
But this query gaves me an error : invalid input syntax for integer: ""
I saw that the Postgres equivalent to MySQL is COALESCE() so i think i'm on the good way here.
I also know you cannot add varchar to varchar so i tried to cast it to integer to do that. I'm not sure if i casted it correctly with parenthesis at the good place and regarding to error maybe i cannot cast to int with coalesce.
Last thing, i can certainly do a co-related sub-select to update my two tables but i'm a little lost at this point.
The output must be an integer matching the number of questions answered to a backup survey.
Any thoughts?
Thanks.
coalesce() returns the first non-null value from the list supplied. So, if the column value is null the expression COALESCE(t1.valeur_question_4,'') returns an empty string and that's why you get the error.
But it seems you want something completely different: you want check if the column is null (or empty) and then subtract a value if it is to count the number of non-null columns.
To return 1 if a value is not null or 0 if it isn't you can use:
(nullif(valeur_question_4, '') is null)::int
nullif returns null if the first value equals the second. The IS NULL condition returns a boolean (something that MySQL doesn't have) and that can be cast to an integer (where false will be cast to 0 and true to 1)
So the whole expression should be:
nb_question_repondu = 9 - (
(nullif(t1.valeur_question_4,'') is null)::int
+ (nullif(t1.valeur_question_6,'') is null)::int
+ (nullif(t1.valeur_question_7,'') is null)::int
+ (nullif(t1.valeur_question_9,'') is null)::int
)
Another option is to unpivot the columns and do a select on them in a sub-select:
update reponse_question_finale
set nb_question_repondu = (select count(*)
from (
values
(valeur_question_4),
(valeur_question_6),
(valeur_question_7),
(valeur_question_9)
) as t(q)
where nullif(trim(q),'') is not null);
Adding more columns to be considered is quite easy then, as you just need to add a single line to the values() clause
I use this sql to execute sql:
v_sql4 :='
INSERT INTO public.rebatesys(head,contract_no,history_no,f_sin,line_no,s_line_no,departmentcd,catagorycd,jan,seriescd,f_exclude, f_del,ins_date,ins_time,ins_user_id,ins_func_id,ins_ope_id,upd_date,upd_time,upd_user_id,upd_func_id,upd_ope_id)
VALUES (0, '''||v_contract_no||''', '||v_history_no||',1, '||v_line_no||', '||v_down_s_line_no||', '||coalesce(v_deptCD,null)||', '||0||', '''||v_singleJan||''','''||0||''','||v_fExclude||',
0, current_date, current_time, '||v_ins_user_id||', 0, 0,
current_date,current_time,'||v_upd_user_id||',0, 0);';
RAISE NOTICE 'v_sql4 IS : %', v_sql4;
EXECUTE v_sql4;
But when field "v_deptCD" is null,the whole sql is null,even I use coalesce,I still can't do id, the out put is :
NOTICE: v_sql4 IS : <NULL>
How to fix it?
When v_deptCD is null, you want to replace it by the string 'null', not the keyword.
', '||coalesce(v_deptCD,'null')||', '
You can use this
case when v_deptCD notnull then v_deptCD else null end
or use this for string concatination inside sql
concat(field1, ', ', field2)
Alternative approach to JGH solution is to use function format(your_string, list, of, values), it can ignore NULL values, but has the option to display them as NULL if you use %L in your format string. It will however single quote numbers if you use that format specifier, requiring casting in some cases.
Format arguments according to a format string. This function is similar to the C function sprintf. See Section 9.4.1.
But in my opinion best solution is to use USING clause and pass values in there. It looks kinda like prepared statement, protects you from SQL Injection, but does not cache plans like prepared statements. There are simple examples on how to do this in documentation for executing dynamic commands.
EXECUTE 'SELECT count(*) FROM mytable WHERE inserted_by = $1 AND inserted <= $2'
INTO c
USING checked_user, checked_date;
I have the problem with the following CTE expression because prev_count in new_values is being interpreted as text, but the column I'm updating in counts is type integer. I'm getting this error on the marked line:
ERROR: column "prev_count" is of type integer but expression is of type text
LINE 12: prev_count = new_values.prev_count
Here's the query:
WITH
new_values (word,count,txid,prev_count) AS (
VALUES ('cat',1,5,NULL)),
updated AS (
UPDATE
counts t
SET
count = new_values.count,
txid = new_values.txid,
prev_count = new_values.prev_count -- ERROR HERE
FROM
new_values
WHERE (
t.word = new_values.word
)
RETURNING t.*)
INSERT INTO counts(
word,count,txid,prev_count
) SELECT
word,count,txid,prev_count FROM new_values
WHERE NOT EXISTS (
SELECT 1 FROM updated WHERE (updated.word = new_values.word))
My question is, what's an elegant way to fix the error? I would rather specify the type of prev_count in new_values instead of adding an explicit cast, but I don't see anything like that in the docs.
Adding this here as an explicit answer along with a detailed explanation.
The fix is:
WITH
new_values (word,count,txid,prev_count) AS (
VALUES ('cat',1,5,NULL::text)),
As a_horse_with_no_name suggested in the comments.
Why is this necessary? Because the row specification comes from the VALUES section and NULL is unknown. In this case PostgreSQL helpfully casts to text. But that is not what you want so you have to give a type to the NULL.
This often comes up in other cases too, such as UNION statements where a NULL in the first segment in the column list can be given an implicit type which clashes with the type of the column in another segment. So this is a tricky corner worth knowing about.
What is the argument type for the order by clause in Postgresql?
I came across a very strange behaviour (using Postgresql 9.5). Namely, the query
select * from unnest(array[1,4,3,2]) as x order by 1;
produces 1,2,3,4 as expected. However the query
select * from unnest(array[1,4,3,2]) as x order by 1::int;
produces 1,4,3,2, which seems strange. Similarly, whenever I replace 1::int with whatever function (e.g. greatest(0,1)) or even case operator, the results are unordered (on the contrary to what I would expect).
So which type should an argument of order by have, and how do I get the expected behaviour?
This is expected (and documented) behaviour:
A sort_expression can also be the column label or number of an output column
So the expression:
order by 1
sorts by the first column of the result set (as defined by the SQL standard)
However the expression:
order by 1::int
sorts by the constant value 1, it's essentially the same as:
order by 'foo'
By using a constant value for the order by all rows have the same sort value and thus aren't really sorted.
To sort by an expression, just use that:
order by
case
when some_column = 'foo' then 1
when some_column = 'bar' then 2
else 3
end
The above sorts the result based on the result of the case expression.
Actually I have a function with an integer argument which indicates the column to be used in the order by clause.
In a case when all columns are of the same type, this can work: :
SELECT ....
ORDER BY
CASE function_to_get_a_column_number()
WHEN 1 THEN column1
WHEN 2 THEN column2
.....
WHEN 1235 THEN column1235
END
If columns are of different types, you can try:
SELECT ....
ORDER BY
CASE function_to_get_a_column_number()
WHEN 1 THEN column1::varchar
WHEN 2 THEN column2::varchar
.....
WHEN 1235 THEN column1235::varchar
END
But these "workarounds" are horrible. You need some other approach than the function returning a column number.
Maybe a dynamic SQL ?
I would say that dynamic SQL (thanks #kordirko and the others for the hints) is the best solution to the problem I originally had in mind:
create temp table my_data (
id serial,
val text
);
insert into my_data(id, val)
values (default, 'a'), (default, 'c'), (default, 'd'), (default, 'b');
create function fetch_my_data(col text)
returns setof my_data as
$f$
begin
return query execute $$
select * from my_data
order by $$|| quote_ident(col);
end
$f$ language plpgsql;
select * from fetch_my_data('val'); -- order by val
select * from fetch_my_data('id'); -- order by id
In the beginning I thought this could be achieved using case expression in the argument of the order by clause - the sort_expression. And here comes the tricky part which confused me: when sort_expression is a kind of identifier (name of a column or a number of a column), the corresponding column is used when ordering the results. But when sort_expression is some value, we actually order the results using that value itself (computed for each row). This is #a_horse_with_no_name's answer rephrased.
So when I queried ... order by 1::int, in a way I have assigned value 1 to each row and then tried to sort an array of ones, which clearly is useless.
There are some workarounds without dynamic queries, but they require writing more code and do not seem to have any significant advantages.