I have a column which is of an array type. I want to use the where condition in my script, but am unable to. The unnest formula is too complex to use and I want to keep it simple here.
I have 4 columns. One of them is called box_number. It can have an array of multiple numbers. I want to search for rows where box_number contains 123.
select
*
from BOX_TABLE
where box_number is {123}
ERROR: syntax error at or near "{"
SELECT * FROM BOX_TABLE WHERE 123 = ANY (box_number);
You check that at least one value inside the column is 123.
To test for equality, try
WHERE box_number = ARRAY[123]
To test if the array contains your value, use the “contains” operator &&:
WHERE box_number && ARRAY[123]
Related
I am trying to clean up a table that has a very messy varchar column, with entries of the sorts:
<u><font color="#0000FF">VA Lidar</font></u> OR <u><font color="#0000FF">InPort Metadata</font></u>
I would like to update the column by keeping only the html links, and separating them with a coma if there are more than one. Ideally I would do something like this:
UPDATE mytable
SET column = array_to_string(regexp_matches(column,'(?<=href=").+?(?=\")','g') , ',');
But unfortunately this returns an error in Postgres 10:
ERROR: set-returning functions are not allowed in UPDATE
I assume regexp_matches() is the said set-returning function. Any ideas on how I can achieve this?
Notes
1.
You don't need to base the correlated subquery on a separate instance of the base table (like other answers suggested). That would be doing more work for nothing.
2.
For simple cases an ARRAY constructor is cheaper than array_agg(). See:
Why is array_agg() slower than the non-aggregate ARRAY() constructor?
3.
I use a regular expression without lookahead and lookbehind constraints and parentheses instead: href="([^"]+)
See query 1.
This works because parenthesized subexpressions are captured by regexp_matches() (and several other Postgres regexp functions). So we can replace the more sophisticated constraints with plain parentheses. The manual on regexp_match():
If a match is found, and the pattern contains no parenthesized
subexpressions, then the result is a single-element text array
containing the substring matching the whole pattern. If a match is
found, and the *pattern* contains parenthesized subexpressions, then the
result is a text array whose n'th element is the substring matching
the n'th parenthesized subexpression of the pattern
And for regexp_matches():
This function returns no rows if there is no match, one row if there
is a match and the g flag is not given, or N rows if there are N
matches and the g flag is given. Each returned row is a text array
containing the whole matched substring or the substrings matching
parenthesized subexpressions of the pattern, just as described above
for regexp_match.
4.
regexp_matches() returns a set of arrays (setof text[]) for a reason: not only can a regular expression match several times in a single string (hence the set), it can also produce multiple strings for each single match with multiple capturing parentheses (hence the array). Does not occur with this regexp, every array in the result holds a single element. But future readers shall not be lead into a trap:
When feeding the resulting 1-D arrays to array_agg() (or an ARRAY constructor) that produces a 2-D array - which is only even possible since Postgres 9.5 added a variant of array_agg() accepting array input. See:
Is there something like a zip() function in PostgreSQL that combines two arrays?
However, quoting the manual:
inputs must all have same dimensionality, and cannot be empty or NULL
I think this can never fail as the same regexp always produces the same number of array elements. Ours always produces one element. But that may be different with other regexp. If so, there are various options:
Only take the first element with (regexp_matches(...))[1]. See query 2.
Unnest arrays and use string_agg() on base elements. See query 3.
Each approach works here, too.
Query 1
UPDATE tbl t
SET col = (
SELECT array_to_string(ARRAY(SELECT regexp_matches(col, 'href="([^"]+)', 'g')), ',')
);
Columns with no match are set to '' (empty string).
Query 2
UPDATE tbl
SET col = (
SELECT string_agg(t.arr[1], ',')
FROM regexp_matches(col, 'href="([^"]+)', 'g') t(arr)
);
Columns with no match are set to NULL.
Query 3
UPDATE tbl
SET col = (
SELECT string_agg(elem, ',')
FROM regexp_matches(col, 'href="([^"]+)', 'g') t(arr)
, unnest(t.arr) elem
);
Columns with no match are set to NULL.
db<>fiddle here (with extended test case)
You could use a correlated subquery to deal with the offending set-returning function (which is regexp_matches). Something like this:
update mytable
set column = (
select array_to_string(array_agg(x), ',')
from (
select regexp_matches(t2.c, '(?<=href=").+?(?=\")', 'g')
from t t2
where t2.id = t.id
) dt(x)
)
You're still stuck with the "CSV in a column" nastiness but that's a separate issue and presumably not a problem for you.
Building on the approach of mu is too short with slightly different regex and a COALESCE function to retain values that do not contain href-links:
UPDATE a
SET bad_data = COALESCE(
(SELECT Array_to_string(Array_agg(x), ',')
FROM (SELECT Regexp_matches(a.bad_data,
'(?<=href=")[^"]+', 'g'
) AS x
FROM a a2
WHERE a2.id = a.id) AS sub), bad_data
);
SQL Fiddle
How to find string values in text array using SQL query.
Suppose I have:
id location
1 {Moscow,New york}
2 {Mumbai}
3 {California,Texas}
I want to find id whose location is Moscow.I used:
select id from table where location in ('Moscow'); but get error:
ERROR: malformed array literal: "Moscow"
LINE 1: select id from table where location in ('Moscow');
DETAIL: Array value must start with "{" or dimension information.
I am using Postgres.
For DataType=Array, you can use the method=Any.
select id from table where 'Moscow' = Any(location)
As the document which describes DataType=Array:
8.14.5. Searching in Arrays
To search for a value in an array, each value must be checked. This
can be done manually, if you know the size of the array.
or use the method = Any:
9.21.3. ANY/SOME (array)
expression operator ANY (array expression) expression operator SOME
(array expression) The right-hand side is a parenthesized expression,
which must yield an array value. The left-hand expression is evaluated
and compared to each element of the array using the given operator,
which must yield a Boolean result. The result of ANY is "true" if any
true result is obtained. The result is "false" if no true result is
found (including the case where the array has zero elements).
For Searching in Array DataType you can use the ANY()
SELECT id FROM table WHERE 'Moscow' = ANY(location);
Live Demo
http://sqlfiddle.com/#!17/a6c3a/2
select id from demo where location like '%Moscow'%'
I am trying to SELECT and parse a javascript list in a postgres table column, it has no keys:
{coastal,transitional,contemporary,romantic,traditional,
industrial,modern,contemporary_eclectic,regency,mediterranean}
What SQL command get's the nth value?
I know you can get values by key like this:
SELECT {column_name}->>{key value}
FROM {table_name}
But I really want to just pull values by list-value order. Is there some syntax that I cannot find? Or do I need to transform this array into a different data type?
The same actually works for arrays:
{column_name}->>N
where N is the integer position of an element.
References:
https://www.postgresql.org/docs/current/static/functions-json.html
Turns out I asked the wrong question--I have a postgres array, not a JSON:
I was struggling because posgres starts counting arrays at position 1, not 0--doh!
{column_name}[1] //this is the first value in the array
Using Postgres 9.0, I need a way to test if a value exists in a given array. So far I came up with something like this:
select '{1,2,3}'::int[] #> (ARRAY[]::int[] || value_variable::int)
But I keep thinking there should be a simpler way to this, I just can't see it. This seems better:
select '{1,2,3}'::int[] #> ARRAY[value_variable::int]
I believe it will suffice. But if you have other ways to do it, please share!
Simpler with the ANY construct:
SELECT value_variable = ANY ('{1,2,3}'::int[])
The right operand of ANY (between parentheses) can either be a set (result of a subquery, for instance) or an array. There are several ways to use it:
SQLAlchemy: how to filter on PgArray column types?
IN vs ANY operator in PostgreSQL
Important difference: Array operators (<#, #>, && et al.) expect array types as operands and support GIN or GiST indices in the standard distribution of PostgreSQL, while the ANY construct expects an element type as left operand and can be supported with a plain B-tree index (with the indexed expression to the left of the operator, not the other way round like it seems to be in your example). Example:
Index for finding an element in a JSON array
None of this works for NULL elements. To test for NULL:
Check if NULL exists in Postgres array
Watch out for the trap I got into: When checking if certain value is not present in an array, you shouldn't do:
SELECT value_variable != ANY('{1,2,3}'::int[])
but use
SELECT value_variable != ALL('{1,2,3}'::int[])
instead.
but if you have other ways to do it please share.
You can compare two arrays. If any of the values in the left array overlap the values in the right array, then it returns true. It's kind of hackish, but it works.
SELECT '{1}' && '{1,2,3}'::int[]; -- true
SELECT '{1,4}' && '{1,2,3}'::int[]; -- true
SELECT '{4}' && '{1,2,3}'::int[]; -- false
In the first and second query, value 1 is in the right array
Notice that the second query is true, even though the value 4 is not contained in the right array
For the third query, no values in the left array (i.e., 4) are in the right array, so it returns false
unnest can be used as well.
It expands array to a set of rows and then simply checking a value exists or not is as simple as using IN or NOT IN.
e.g.
id => uuid
exception_list_ids => uuid[]
select * from table where id NOT IN (select unnest(exception_list_ids) from table2)
Hi that one works fine for me, maybe useful for someone
select * from your_table where array_column ::text ilike ANY (ARRAY['%text_to_search%'::text]);
"Any" works well. Just make sure that the any keyword is on the right side of the equal to sign i.e. is present after the equal to sign.
Below statement will throw error: ERROR: syntax error at or near "any"
select 1 where any('{hello}'::text[]) = 'hello';
Whereas below example works fine
select 1 where 'hello' = any('{hello}'::text[]);
When looking for the existence of a element in an array, proper casting is required to pass the SQL parser of postgres. Here is one example query using array contains operator in the join clause:
For simplicity I only list the relevant part:
table1 other_name text[]; -- is an array of text
The join part of SQL shown
from table1 t1 join table2 t2 on t1.other_name::text[] #> ARRAY[t2.panel::text]
The following also works
on t2.panel = ANY(t1.other_name)
I am just guessing that the extra casting is required because the parse does not have to fetch the table definition to figure the exact type of the column. Others please comment on this.
I found a weird problem with MySQL select statement having "IN" in where clause:
I am trying this query:
SELECT ads.*
FROM advertisement_urls ads
WHERE ad_pool_id = 5
AND status = 1
AND ads.id = 23
AND 3 NOT IN (hide_from_publishers)
ORDER BY rank desc
In above SQL hide_from_publishers is a column of advertisement_urls table, with values as comma separated integers, e.g. 4,2 or 2,7,3 etc.
As a result, if hide_from_publishers contains same above two values, it should return only record for "4,2" but it returns both records
Now, if I change the value of hide_for_columns for second set to 3,2,7 and run the query again, it will return single record which is correct output.
Instead of hide_from_publishers if I use direct values there, i.e. (2,7,3) it does recognize and returns single record.
Any thoughts about this strange problem or am I doing something wrong?
There is a difference between the tuple (1, 2, 3) and the string "1, 2, 3". The former is three values, the latter is a single string value that just happens to look like three values to human eyes. As far as the DBMS is concerned, it's still a single value.
If you want more than one value associated with a record, you shouldn't be storing it as a comma-separated value within a single field, you should store it in another table and join it. That way the data remains structured and you can use it as part of a query.
You need to treat the comma-delimited hide_from_publishers column as a string. You can use the LOCATE function to determine if your value exists in the string.
Note that I've added leading and trailing commas to both strings so that a search for "3" doesn't accidentally match "13".
select ads.*
from advertisement_urls ads
where ad_pool_id = 5
and status = 1
and ads.id = 23
and locate(',3,', ','+hide_from_publishers+',') = 0
order by rank desc
You need to split the string of values into separate values. See this SO question...
Can Mysql Split a column?
As well as the supplied example...
http://blog.fedecarg.com/2009/02/22/mysql-split-string-function/
Here is another SO question:
MySQL query finding values in a comma separated string
And the suggested solution:
http://dev.mysql.com/doc/refman/5.0/en/string-functions.html#function_find-in-set