I have table
raw TABLE
=========
id class_ids
------------------------
1 1234,12334,12341,1228
2 12281,12341,12283
3 1234,34221,31233,43434,1123
How to define regex to select raws if class_ids contains special id.
If we select raws with '1234' in class_ids result list should not contain raws with '12341' in class_ids.
IDs in column class_ids separated with ,
SELECT FROM raw re WHERE re.class_ids LIKE (regex)
You shouldn't be storing comma separated values in a single column.
However, this is better done using string_to_array() in Postgres instead of a regex:
SELECT *
FROM raw
WHERE '1234'= any(string_to_array(class_ids, ','));
If you really want to de-normalize your data, it's better to store those numbers in a proper integer array, instead of comma separated list of strings
A simple way uses like:
where ',' || re.class_ids || ',' like '%,1234,%'
However, this is not the real issue. You should not be storing lists of ids in a string. The SQLish way of storing them would have a table with one row per id and one row per class_id. This is called a junction table.
Even if you don't use a separate table, you should at least use Postgres's built-in mechanisms, such as an array. However, a separate table is much the preferred method, because you can explicitly declare foreign key relationships.
If you really want to do this with regular expressions, you can use the ~ operator:
SELECT FROM raw re WHERE re.class_ids ~ '^(^|,)1234(,|$)$';
But I prefer a_horse_with_no_name's answer that uses arrays.
Related
Is it possible to check if a row contains a string without conisdering spaces?
Suppose I have a table like the one above. I want to know if the query column contains a string that may have different consecutive number of space than the one stored or vice versa?
For example: the first row's query is select id, username from postgresql, and the one I want to know if stored in the table is:
select id, username
from postgresql
That is to say the one that I want to know if exists in the table is indented differently and hence has different number of space.
You can use REGEXP_REPLACE; this will likely be very slow on large data set.
SELECT * from table
where REGEXP_REPLACE('select id, username from postgresql ', '\s+$', '') = REGEXP_REPLACE(query, '\s+$', '')
I think you would phrase this as:
where $str ~ replace('select id, username from postgresql', ' ', '[\s]+')
Note: This assumes that your string does not have other regular expression special characters.
I have a field in my database which has a long list of strings separated by commas. Here are few row examples:
HAB
DHAB,RAB,DAB
HAB,RAB,DAB
RAB,HAB,
RAB,HAB,DAB
My query has the following condition:
WHERE description LIKE '%HAB%'
But it returns the second row which has 'DHAB'.
Can it be done using regex with the WHERE statement so that I only get entries which have 'HAB' in the list (one string) and not the entries with 'DHAB'?
You may use
WHERE description ~ '(^|,)HAB($|,)'
The regex matches
(^|,) - start of string or a ,
HAB - literal substring
($|,) - end of string or ,
See the online regex demo.
Regular expressions are powerful and versatile, but also expensive. Consider a different approach: transform the list to an actual array with string_to_array() and then:
WHERE 'HAB' = ANY (string_to_array(description, ',')
Or:
WHERE string_to_array(description, ',') #> '{HAB}'
db<>fiddle here
The latter can be supported with a GIN index, which makes it faster by orders of magnitude for big tables.
CREATE INDEX ON tbl USING gin (string_to_array(description, ','));
Related:
Can PostgreSQL index array columns?
Or consider a normalized DB design replacing the comma-separated values with a 1:n relationship. Related:
How to implement a many-to-many relationship in PostgreSQL?
Can PostgreSQL have a uniqueness constraint on array elements?
I have a database that contains columns that are text fields (strings, a few sentences long) and columns that are shorter strings (eg: college majors). Is there any way I can use the 'LIKE' function in SQL to search whether one of the values of the College Major column appears in another column?
I don't want to write out each of the college majors as a string since there are over 100.
Yes you can. Something like
where bigdatacolumn like '%' + computer_major + '%'
Since you said, other column contains few lines (Text column), you probably want to consider using Full Text Search instead of using LIKE operator
Use The ANY operator to compare in an array as shown in the below query.
select * from staff where department ILIKE ANY ( ARRAY['AUT%', '%COM%' ,'SP%' ] :: TEXT[] );
I would like to ask if it is possible to do this:
For example the search string is '009' -> (consider the digits as string)
is it possible to have a query that will return any occurrences of this on the database not considering the order.
for this example it will return
'009'
'090'
'900'
given these exists on the database. thanks!!!!
Use the Like operator.
For Example :-
SELECT Marks FROM Report WHERE Marks LIKE '%009%' OR '%090%' OR '%900%'
Split the string into individual characters, select all rows containing the first character and put them in a temporary table, then select all rows from the temporary table that contain the second character and put these in a temporary table, then select all rows from that temporary table that contain the third character.
Of course, there are probably many ways to optimize this, but I see no reason why it would not be possible to make a query like that work.
It can not be achieved in a straight forward way as there is no sort() function for a particular value like there is lower(), upper() functions.
But there is some workarounds like -
Suppose you are running query for COL A, maintain another column SORTED_A where from application level you keep the sorted value of COL A
Then when you execute query - sort the searchToken and run select query with matching sorted searchToken with the SORTED_A column
After running my query I get 1 column result as
5
6
98
101
Is there a way to store this result as array so that I can use it later
in queries like
WHERE NOT IN ('5','6','98','101')
I am aware of storing single variable results but is this possible?
I can not use #Table variable as I will be rerunning the query again in the future and it goes out of scope
There are multiple way of storing those column data like using Temporary Tables or View or Table valued function but IMO there is no need of storing that column data anywhere. You can directly use that column in any query saying below (or) perform a JOIN which would be much better option than NOT IN
select * from
table2
where some_column not in (select column1 from this_table);
While this method is not recommended, storing an array in a single column can be done using CSV's(Comma Separated Values). Simply create a VARCHAR array and store it by storing a string containing the values in a specific order. Basically store all of your values into a string with each value being separated by a comma in that string. Store that into a column of your choice. You can later fetch the string and parse it with a string parser i.e using the .split() function in python. AGAIN I do not recommend doing this, I would instead use multiple columns, one referring to each value and access them that way instead
Using separate columns would make it easy to use in a Stored Procedure.