I am using tsvectors to search for similar entries in a list of keyword I have. In this way I am able to consider the following keyword are identical:
IT security governance
it security government
The Problem is that, due to the stopwords logic, also the following entries are considered similar:
IT environment
Environment
So, I would like to have a way to detect which records contains stopwords, so that I can treat them differently.
I can add a boolean value to the record to know if it contains stopwords or not.
Any idea ?
You can use ts_debug to find the lexemes that are generated by full text search:
SELECT array_agg(lexemes[1]) FILTER (WHERE lexemes[1] IS NOT NULL)
FROM ts_debug('english', 'IT security governance')
WHERE alias IN ('asciiword', 'word');
array_agg
----------------
{secur,govern}
(1 row)
To find if there is a stop present, you can look if the lexeme is NULL:
SELECT token
FROM ts_debug('english', 'IT security governance')
WHERE alias IN ('asciiword', 'word')
AND lexemes[1] IS NULL;
token
-------
IT
(1 row)
Based on the suggetion of #Laurenz-Albe I came up with this more general solution; based on the value returned by this queries I can distinguish entries with stowords from those that don't have any:
select count(*) FROM ts_debug('english', 'IT security governance')
where array_length(lexemes,1) = 0
select count(*) FROM ts_debug('english', 'advanced security governance')
where array_length(lexemes,1) = 0
Related
The question: I have a list of sales quotations and many of them are not valid as they are simply in the system for practice or training. Usually the quotation name contains the word 'Test' or 'Dummy'. (In a couple of instances the quote_name contains 'Prova' - which happens to be Italian for 'Test').
Given that I cannot easily control the list of strings to search for, I decided to maintain the list in a second table - 'Terms to Search for'. A simple one column table with a list of terms ('Test', 'Prova', 'Dummy', ...).
In Amazon Redshift, I tried a simple CASE statement:
CASE WHEN UPPER(vx.quote_name) LIKE ('%' + UPPER(terms.term) + '%') THEN 'Y' ELSE 'N' END AS "Any DPS"
However, that seems to only get the first search term in the list.
Also, for the same quotation, which can have multiple rows due to multiple items being sold, I usually get one row set to 'Y' and the rest set to 'N'.
I modified the statement to:
---- #4a: get a list of the quotes whose quote_names match the patterns in the list
SELECT
vx.master_quote_number,
'Y' AS "Any DPS"
FROM t_quotes vx, any_dps_search_families terms
WHERE UPPER(vx.prod_fmly) IN ('%'+ UPPER(terms.term) +'%');
--- 4b: merge Any DPS results back in
select vx.*, dps."Any DPS"
from t_quotes vx
LEFT JOIN transform_data_4 dps ON (vx.master_quote_number = dps.master_quote_number)
But that isn't doing it either.
Environment: Amazon Redshit (which is mostly like Postgres). An answer to this in Postgres would be ideal. I can switch this clause to MySQL if needed but I'd rather not.
This is a case for lateral joins (untested):
SELECT vx.master_quote_number
FROM any_dps_search_families terms
CROSS JOIN LATERAL (SELECT master_quote_number
FROM t_quotes
WHERE UPPER(prod_fmly)
LIKE ('%' || UPPER(terms.term) || '%')
) vx;
I know about full-text search, but that only matches your query against individual words. I want to select strings that contain a word that starts with words in my query. For example, if I search:
appl
the following should match:
a really nice application
apples are cool
appliances
since all those strings contains words that start with appl. In addition, it would be nice if I could select the number of words that match, and sort based on that.
How can I implement this in PostgreSQL?
Prefix matching with Full Text Search
FTS supports prefix matching. Your query works like this:
SELECT * FROM tbl
WHERE to_tsvector('simple', string) ## to_tsquery('simple', 'appl:*');
Note the appended :* in the tsquery. This can use an index.
See:
Get partial match from GIN indexed TSVECTOR column
Alternative with regular expressions
SELECT * FROM tbl
WHERE string ~ '\mappl';
Quoting the manual here:
\m .. matches only at the beginning of a word
To order by the count of matches, you could use regexp_matches()
SELECT tbl_id, count(*) AS matches
FROM (
SELECT tbl_id, regexp_matches(string, '\mappl', 'g')
FROM tbl
WHERE string ~ '\mappl'
) sub
GROUP BY tbl_id
ORDER BY matches DESC;
Or regexp_split_to_table():
SELECT tbl_id, string, count(*) - 1 AS matches
FROM (
SELECT tbl_id, string, regexp_split_to_table(string, '\mappl')
FROM tbl
WHERE string ~ '\mappl'
) sub
GROUP BY 1, 2
ORDER BY 3 DESC, 2, 1;
db<>fiddle here
Old sqlfiddle
Postgres 9.3 or later has index support for simple regular expressions with a trigram GIN or GiST index. The release notes for Postgres 9.3:
Add support for indexing of regular-expression searches in pg_trgm
(Alexander Korotkov)
See:
PostgreSQL LIKE query performance variations
Depesz wrote a blog about index support for regular expressions.
SELECT * FROM some_table WHERE some_field LIKE 'appl%' OR some_field LIKE '% appl%';
As for counting the number of words that match, I believe that would be too expensive to do dynamically in postgres (though maybe someone else knows better). One way you could do it is by writing a function that counts occurrences in a string, and then add ORDER BY myFunction('appl', some_field). Again though, this method is VERY expensive (i.e. slow) and not recommended.
For things like that, you should probably use a separate/complimentary full-text search engine like Sphinx Search (google it), which is specialized for that sort of thing.
An alternative to that, is to have another table that contains keywords and the number of occurrences of those keywords in each string. This means you need to store each phrase you have (e.g. really really nice application) and also store the keywords in another table (i.e. really, 2, nice, 1, application, 1) and link that keyword table to your full-phrase table. This means that you would have to break up strings into keywords as they are entered into your database and store them in two places. This is a typical space vs speed trade-off.
I am getting this error in the pg production mode, but its working fine in sqlite3 development mode.
ActiveRecord::StatementInvalid in ManagementController#index
PG::Error: ERROR: column "estates.id" must appear in the GROUP BY clause or be used in an aggregate function
LINE 1: SELECT "estates".* FROM "estates" WHERE "estates"."Mgmt" = ...
^
: SELECT "estates".* FROM "estates" WHERE "estates"."Mgmt" = 'Mazzey' GROUP BY user_id
#myestate = Estate.where(:Mgmt => current_user.Company).group(:user_id).all
If user_id is the PRIMARY KEY then you need to upgrade PostgreSQL; newer versions will correctly handle grouping by the primary key.
If user_id is neither unique nor the primary key for the 'estates' relation in question, then this query doesn't make much sense, since PostgreSQL has no way to know which value to return for each column of estates where multiple rows share the same user_id. You must use an aggregate function that expresses what you want, like min, max, avg, string_agg, array_agg, etc or add the column(s) of interest to the GROUP BY.
Alternately you can rephrase the query to use DISTINCT ON and an ORDER BY if you really do want to pick a somewhat arbitrary row, though I really doubt it's possible to express that via ActiveRecord.
Some databases - including SQLite and MySQL - will just pick an arbitrary row. This is considered incorrect and unsafe by the PostgreSQL team, so PostgreSQL follows the SQL standard and considers such queries to be errors.
If you have:
col1 col2
fred 42
bob 9
fred 44
fred 99
and you do:
SELECT col1, col2 FROM mytable GROUP BY col1;
then it's obvious that you should get the row:
bob 9
but what about the result for fred? There is no single correct answer to pick, so the database will refuse to execute such unsafe queries. If you wanted the greatest col2 for any col1 you'd use the max aggregate:
SELECT col1, max(col2) AS max_col2 FROM mytable GROUP BY col1;
I recently moved from MySQL to PostgreSQL and encountered the same issue. Just for reference, the best approach I've found is to use DISTINCT ON as suggested in this SO answer:
Elegant PostgreSQL Group by for Ruby on Rails / ActiveRecord
This will let you get one record for each unique value in your chosen column that matches the other query conditions:
MyModel.where(:some_col => value).select("DISTINCT ON (unique_col) *")
I prefer DISTINCT ON because I can still get all the other column values in the row. DISTINCT alone will only return the value of that specific column.
After often receiving the error myself I realised that Rails (I am using rails 4) automatically adds an 'order by id' at the end of your grouping query. This often results in the error above. So make sure you append your own .order(:group_by_column) at the end of your Rails query. Hence you will have something like this:
#problems = Problem.select('problems.username, sum(problems.weight) as weight_sum').group('problems.username').order('problems.username')
#myestate1 = Estate.where(:Mgmt => current_user.Company)
#myestate = #myestate1.select("DISTINCT(user_id)")
this is what I did.
I'm fairly proficient in mySQL and MSSQL, but I'm just getting started with postgres. I'm sure this is a simple issue, so to be brief:
SQL error:
ERROR: column "incidents.open_date" must appear in the GROUP BY clause or be used in an aggregate function
In statement:
SELECT date(open_date), COUNT(*)
FROM incidents
GROUP BY 1
ORDER BY open_date
The type for open_date is timestamp with time zone, and I get the same results if I use GROUP BY date(open_date).
I've tried going over the postgres docs and some examples online, but everything seems to indicate that this should be valid.
The problem is with the unadorned open_date in the ORDER BY clause.
This should do it:
SELECT date(open_date), COUNT(*)
FROM incidents
GROUP BY date(open_date)
ORDER BY date(open_date);
This would also work (though I prefer not to use integers to refer to columns for maintenance reasons):
SELECT date(open_date), COUNT(*)
FROM incidents
GROUP BY 1
ORDER BY 1;
"open_date" is not in your select list, "date(open_date)" is.
Either of these will work:
order by date(open_date)
order by 1
You can also name your columns in the select statement, and then refer to that alias:
select date(open_date) "alias" ... order by alias
Some databases require the keyword, AS, before the alias in your select.
I have created a database as part of university assignment and I have hit a snag with the question in the title.
More likely I am being asked to find out how many films each company has made. Which suggests to me a group by query. But I have no idea where to begin. It is only a two mark question but the syntax is not clicking in my head.
My schema is:
CREATE TABLE Movie
(movieID CHAR(3) ,
title CHAR(36),
year NUMBER,
company CHAR(50),
totalNoms NUMBER,
awardsWon NUMBER,
DVDPrice NUMBER(5,2),
discountPrice NUMBER(5,2))
There are other tables but at first glance I don't think they are relevant to this question.
I am using sqlplus10
The answer you need comes from three basic SQL concepts, I'll step through them with you. If you need more assistance to create an answer from these hints, let me know and I can try to keep guiding you.
Group By
As you mentioned, SQL offers a GROUP BY function that can help you.
A SQL Query utilizing GROUP BY would look like the following.
SELECT list, fields, aggregate(value)
FROM tablename
--WHERE goes here, if you need to restrict your result set
GROUP BY list, fields
a GROUP BY query can only return fields listed in the group by statement, or aggregate functions acting on each group.
Aggregate Functions
Your homework question also needs an Aggregate function called Count. This is used to count the results returned. A simple query like the following returns the count of all records returned.
SELECT Count(*)
FROM tablename
The two can be combined, allowing you to get the Count of each group in the following way.
SELECT list, fields, count(*)
FROM tablename
GROUP BY list, fields
Column Aliases
Another answer also tried to introduce you to SQL column aliases, but they did not use SQLPLUS syntax.
SELECT Count(*) as count
...
SQLPLUS column alias syntax is shown below.
SELECT Count(*) "count"
...
I'm not going to provide you the SQL, but instead a way to think about it.
What you want to do is select where the company matches and count the total rows returned. That count is the number of films made by the specified company.
Hope that points you in the right direction.
Select company, count(*) AS count
from Movie
group by company
select * group by company won't work in Oracle.