I am using Orient DB 2.1.16. I have a vertex class in orientDB called person, I also created a property for person class called name. I added a full text index on that property called person.name. I have a person type vertex where name property equals 'abcd'. When searching on index with query SELECT FROM INDEX:person.name WHERE KEY CONTAINSTEXT 'abc' I get correct resultset but when I search on the same index with only two characters I get no result back SELECT FROM INDEX:person.name WHERE KEY CONTAINSTEXT 'ab'.I don't understand why searching with on two characters does not return any results.
Related
Using a FTS5 virtual table returns nothing for postfix searches.
It only can search for the entire word tokens, or for the prefixes of the word tokens if I append * to the search.
For example, it does not find qwerty.png row, if I search for werty.
CREATE TABLE IF NOT EXISTS files (name TEXT, id INTEGER);
INSERT INTO files (name, id) VALUES ('qwerty.png', 1), ('asdfgh.png', 2);
CREATE VIRTUAL TABLE IF NOT EXISTS names USING FTS5(name);
INSERT INTO names (name) SELECT name FROM files;
SELECT *
FROM names
WHERE name MATCH 'werty';
It only works for prefix searches (qwerty, qwer*, qwe*, ...).
I can't use * at the start of the search (*werty), since it produces an error.
Is possibly to make the indexed text search working as if I would use
SELECT *
FROM names
WHERE name like '%wert%';
?
I just want to have the fast search for a substring without the full table scan.
Perhaps try the experimental trigram tokenizer
When using the trigram tokenizer, a query or phrase token may match any sequence of characters within a row, not just a complete token.
Problem description
I want to search for the query = Angela in a database from a table called Variations. The problem is that the database does not Angela. It contains Angel. As you can see the a is missing.
Searching procedure
The table that I want to query is the following:
"CREATE TABLE IF NOT EXISTS VARIATIONS
(ID INTEGER PRIMARY KEY NOT NULL,
ID_ENTITE INTEGER,
NAME TEXT,
TYPE TEXT,
LANGUAGE TEXT);"
To search for the query I am using fts4 because it is faster than LIKE% especially if I have a big database with more than 10 millions rows. I cannot also use the equality since i am looking for substrings.
I create a virtual table create virtual table variation_virtual using fts4(ID, ID_ENTITE, NAME, TYPE, LANGUAGE);
Filled the virtual table with VARIATIONS insert into variation_virtual select * from VARIATIONS;
The selection query is represented as follow:
SELECT ID_ENTITE, NAME FROM variation_virtual WHERE NAME MATCH "Angela";
Question
What am I missing in the query. What I am doing is the opposite of when we want to check if a query is a subtring of a string in a table.
You can't use fts4 for this. From the documentation:
SELECT count(*) FROM enrondata1 WHERE content MATCH 'linux'; /* 0.03 seconds */
SELECT count(*) FROM enrondata2 WHERE content LIKE '%linux%'; /* 22.5 seconds */
Of course, the two queries above are not
entirely equivalent. For example the LIKE query matches rows that
contain terms such as "linuxophobe" or "EnterpriseLinux" (as it
happens, the Enron E-Mail Dataset does not actually contain any such
terms), whereas the MATCH query on the FTS3 table selects only those
rows that contain "linux" as a discrete token. Both searches are
case-insensitive.
So your query will only match strings that have 'Angela' as a word (at least that is how I interpret 'discrete token').
I am new to GAE, please excuse for being naive.
datastore viewer query with where clause returns "No results in Empty namespace.".
For instance:
select * from GaeUser
returns all the entires.
Something like,
select * from GaeUser where firstName = 'somename'
or
select * from GaeUser where dayOfBirth = 5
returns nothing but the message No results in empty namespace.
I am expecting some pointers on how to debug this.
Thanks for reading this!!
Simply you just wrote an incorrect/misspelled query.
Note that GAE datastore is schema-less. Writing a query for a nonexisting entity or for a nonexisting property or specifying a filter condition where you use an incorrect data type will not result in error but rather in an empty result.
Being schema-less also means that 2 entities of the same kind might have the same property with different types. For example you might have a Person entity with an age property of type int and another Person with an age property of type String. Obviously in this case if you write something like
select * from Person where age='5'
will not return the person who has age=5 property having int type.
So just simply double check the names and types of the entity and properties and try again.
Another important note:
Properties are indexed by default. This means when saving an entity, index records for an indexed property will automatically be created and saved, this allows you to find this entity by this indexed property. Properties can be made unindexed. When you save an entity with an unindexed property, index records will not be saved (or if there were any, they will be removed) for this unindexed property and you will not be able to query/find this entity by this unindexed property.
I am new to idexes and DB optimization. I know there is simple index for one
CREATE index ON table(col)
possibly B-Tree will be created and search capabilities will be improved.
But what is happen for 2 columns index ? And why is the order of defnition important?
CREATE index ON table(col1, col2)
Yes, B-Tree index will be created in most of the database if you didn't specify other type of index. Composite index is useful when the combined selectivity of the composite columns happed on the queries.
The order of the columns on the composite index is important as searching by giving exact values for all the fields included in the index leads to minimal search time but search uses only the first field to retrieve all matched recaords if we provide the values partially with first field.
I found following example for your understanding:
In the phone book example with an composite index created on the columns (city, last_name, first_name), if we search by giving exact values for all the three fields, search time is minimal—but if we provide the values for city and first_name only, the search uses only the city field to retrieve all matched records. Then a sequential lookup checks the matching with first_name. So, to improve the performance, one must ensure that the index is created on the order of search columns.
I have two tables in SQLite:
CREATE TABLE article (body TEXT)
CREATE TABLE article_word (
word TEXT,
article_rowid INTEGER,
FOREIGN KEY(article_rowid) REFERENCES article(rowid),
PRIMARY KEY(word, article_rowid)
)
The program stores long strings in article.body and, for each word in the string, it stores a lowercase version of the word along with the article's rowid in article_word.
I want to let the user search for articles by the first case-insensitive characters in a word, so a search for baz yields an article containing foobar Bazquux spambacon.
How can I modify the tables/add more (if necessary) and query them for matches optimally? Does
SELECT a.rowid, a.body FROM article a, article_word w WHERE w.word LIKE "baz%" AND a.rowid = w.article_rowid
take advantage of the PRIMARY KEY index on article_word.word or does it naïvely search every row?
Use NSPredicate to retrive specific Attribute According to your
requirement, and you can also do Mapping with Sqlite as in core Data.