I am using oracle 12c and Sql Developer with json
For this example I have the follow JSON:
{
"id": "12",
"name": "zhelon"
}
So I have created the follow table for this:
create table persons
id number primary key,
person clob,
constraint person check(person is JSON);
The idea is persist in person column the previous JSON and use a the follow query to get that data
SELECT p.person FROM persons p WHERE json_textvalue('$name', 'zhelon')
Talking about perfonce, I am intresting to extract some json field and add new a colum to the table to improve the response time (I don't know if that is possible)
create table persons
id number primary key,
name varchar(2000),
person clob,
constraint person check(person is JSON);
To do this:
SELECT p.person FROM persons p WHERE p.name = 'zhelon';
My question is:
What's the best way to make a query to get data? I want to reduce the response time.
Which query get the data faster ?
SELECT p.person FROM persons p WHERE json_textvalue('$name', 'zhelon')
or
SELECT p.person FROM persons p WHERE p.name = 'zhelon';
You can create a virtual column like this:
ALTER TABLE persons ADD (NAME VARCHAR2(100)
GENERATED ALWAYS AS (JSON_VALUE(person, '$name' returning VARCHAR2)) VIRTUAL);
I don't know the correct syntax of JSON_VALUE but I think you get an idea.
If needed you can also define a index on such columns like any other column.
However, when you run SELECT p.person FROM persons p WHERE p.name = 'zhelon';
I don't know which value takes precedence, p.person from JSON or the column.
Better use a different name in order to be on the safe side:
ALTER TABLE persons ADD (NAME_VAL VARCHAR2(100)
GENERATED ALWAYS AS (JSON_VALUE(person, '$name' returning VARCHAR2)) VIRTUAL);
SELECT p.person FROM persons p WHERE p.NAME_VAL= 'zhelon';
Related
I am learning SQL (postgres) and am trying to insert a record into a table that references records from two other tables, as foreign keys.
Below is the syntax I am using for creating the tables and records:
-- Create a person table + insert single row
CREATE TABLE person (
pname VARCHAR(255) NOT NULL,
PRIMARY KEY (pname)
);
INSERT INTO person VALUES ('personOne');
-- Create a city table + insert single row
CREATE TABLE city (
cname VARCHAR(255) NOT NULL,
PRIMARY KEY (cname)
);
INSERT INTO city VALUES ('cityOne');
-- Create a employee table w/ForeignKey reference
CREATE TABLE employee (
ename VARCHAR(255) REFERENCES person(pname) NOT NULL,
ecity VARCHAR(255) REFERENCES city(cname) NOT NULL,
PRIMARY KEY(ename, ecity)
);
-- create employee entry referencing existing records
INSERT INTO employee VALUES(
SELECT pname FROM person
WHERE pname='personOne' AND <-- ISSUE
SELECT cname FROM city
WHERE cname='cityOne
);
Notice in the last block of code, where I'm doing an INSERT into the employee table, I don't know how to string together multiple SELECT sub-queries to get both the existing records from the person and city table such that I can create a new employee entry with attributes as such:
ename='personOne'
ecity='cityOne'
The textbook I have for class doesn't dive into sub-queries like this and I can't find any examples similar enough to mine such that I can understand how to adapt them for this use case.
Insight will be much appreciated.
There doesn’t appear to be any obvious relationship between city and person which will make your life hard
The general pattern for turning a select that has two base tables giving info, into an insert is:
INSERT INTO table(column,list,here)
SELECT column,list,here
FROM
a
JOIN b ON a.x = b.y
In your case there isn’t really anything to join on because your one-column tables have no column in common. Provide eg a cityname in Person (because it seems more likely that one city has many person) then you can do
INSERT INTO employee(personname,cityname)
SELECT p.pname, c.cname
FROM
person p
JOIN city c ON p.cityname = c.cname
But even then, the tables are related between themselves and don’t need the third table so it’s perhaps something of an academic exercise only, not something you’d do in the real world
If you just want to mix every person with every city you can do:
INSERT INTO employee(personname,cityname)
SELECT pname, cname
FROM
person p
CROSS JOIN city c
But be warned, two people and two cities will cause 4 rows to be inserted, and so on (20 people and 40 cities, 800 rows. Fairly useless imho)
However, I trust that the general pattern shown first will suffice for your learning; write a SELECT that shows the data you want to insert, then simply write INSERT INTO table(columns) above it. The number of columns inserted to must match the number of columns selected. Don’t forget that you can select fixed values if no column from the query has the info (INSERT INTO X(p,c,age) SELECT personname, cityname, 23 FROM ...)
The following will work for you:
INSERT INTO employee
SELECT pname, cname FROM person, city
WHERE pname='personOne' AND cname='cityOne';
This is a cross join producing a cartesian product of the two tables (since there is nothing to link the two). It reads slightly oddly, given that you could just as easily have inserted the values directly. But I assume this is because it is a learning exercise.
Please note that there is a typo in your create employee. You are missing a comma before the primary key.
I want to query two tables at a time to find the key for an artist given their name. The issue is that my data is coming from disparate sources and there is no definitive standard for the presentation of their names (e.g. Forename Surname vs. Surname, Forename) and so to this end I have a table containing definitive names used throughout the rest of my system along with a separate table of aliases to match the varying styles up to each artist.
This is PostgreSQL but apart from the text type it's pretty standard. Substitute character varying if you prefer:
create table Artists (
id serial primary key,
name text,
-- other stuff not relevant
);
create table Aliases (
artist integer references Artists(id) not null,
name text not null
);
Now I'd like to be able to query both sets of names in a single query to obtain the appropriate id. Any way to do this? e.g.
select id from ??? where name = 'Bloggs, Joe';
I'm not interested in revising my schema's idea of what a "name" is to something more structured, e.g. separate forename and surname, since it's inappropriate for the application. Most of my sources don't structure the data, sometimes one or the other name isn't known, it may be a pseudonym, or sometimes the "artist" may be an entity such as a studio.
I think you want:
select a.id
from artists a
where a.name = 'Bloggs, Joe' or
exists (select 1
from aliases aa
where aa.artist = a.id and
aa.name = 'Bloggs, Joe'
);
Actually, if you just want the id (and not other columns), then you can use:
select a.id
from artists a
where a.name = 'Bloggs, Joe'
union all -- union if there could be duplicates
select aa.artist
from aliases aa
where aa.name = 'Bloggs, Joe';
I'm new to the relational database stuff and Im having a hard time understanding how to write a query to do what I want. I have two tables that have a relationship.
CREATE TABLE DocumentGroups (
id INTEGER PRIMARY KEY AUTOINCREMENT,
comments TEXT,
Username TEXT NOT NULL,
)
CREATE TABLE Documents (
id INTEGER PRIMARY KEY,
documentGroupId INT NOT NULL,
documentTypeId INT NOT NULL,
documentTypeName TEXT NOT NULL,
succesfullyUploaded BIT
)
I would like to query the Documents table and get the record count for each username. Here is the query that I came up with:
SELECT Count(*)
FROM DOCUMENTS
JOIN DocumentGroups ON Documents.documentGroupId=DocumentGroups.id
GROUP BY Username
I currently have 2 entries in the Documents table, 1 from each user. This query prints out:
[{Count(*): 1}, {Count(*): 1}]
This looks correct, but is there anyway for me to get he username associated with each count. Right now there is no way of me knowing which count belongs to each user.
You are almost there. Your query already produces one row per user name (that's your group by clause). All that is left to do is to put that column in the select clause as well:
select dg.username, count(*) cnt
from documents d
join documentgroups dg on d.documentgroupid = dg.id
group by dg.username
Side notes:
table aliases make the queries easier to read and write
in a multi-table query, always qualify all columns with the (alias of) table they belong to
you probably want to alias the result of count(*), so it is easier to consume it from your application
I have the classic arrangement for a many to many relation in a small flashcard like application built using SQLite. Every card can have multiple tags, and every tag can have multiple cards. This two entities having each a table with a third table to link records.
This is the table for Cards:
CREATE TABLE Cards (CardId INTEGER PRIMARY KEY AUTOINCREMENT,
Text TEXT NOT NULL,
Answer INTEGER NOT NULL,
Success INTEGER NOT NULL,
Fail INTEGER NOT NULL);
This is the table for Tags:
CREATE TABLE Tags (TagId INTEGER PRIMARY KEY AUTOINCREMENT,
Name TEXT UNIQUE NOT NULL);
This is the cross reference table:
CREATE TABLE CardsRelatedToTags (CardId INTEGER,
TagId INTEGER,
PRIMARY KEY (CardId, TagId));
I need to get a table of cards with their associated tags in a column separated by commas.
I can already get what I need for a single row knowing its Id with the following query:
SELECT Cards.CardId, Cards.Text,
(SELECT group_concat(Tags.Name, ', ') FROM Tags
JOIN CardsRelatedToTags ON CardsRelatedToTags.TagId = Tags.TagId
WHERE CardsRelatedToTags.CardId = 1) AS TagsList
FROM Cards
WHERE Cards.CardId = 1
This will result in something like this:
CardId | Text | TagsList
1 | Some specially formatted text | Tag1, Tag2, TagN...
How to get this type of result (TagsList from group_concat) for every row in Cards using a SQL query? It is advisable to do so from the performance point of view? Or I need to do this sort of "presentation" work in application code using a simpler request to the DB?
Answering your code question:
SELECT
c.CardId,
c.Text,
GROUP_CONCAT(t.Name,', ') AS TagsList
FROM
Cards c
JOIN CardsRelatedToTags crt ON
c.CardId = crt.CardId
JOIN Tags t ON
crt.TagId = t.TagId
WHERE
c.CardId = 1
GROUP BY c.CardId, c.Text
Now, to the matter of performance. Databases are a powerful tool and do not end on simple SELECT statements. You can definitely do what you need inside a DB (even SQLite). It is a bad practice to use a SELECT statement as a feed for one column inside another SELECT. It would require scanning a table to get result for each row in your input.
I'm using Bugzilla, and I essentially want to SELECT * FROM bugs table in the "bugs" database. However, the "assigned_to" column actually contains integer values (IDs) instead of a string with the user name.
These IDs match primary keys in the "profiles" table (the "userid" column), and the string I want my query to return is actually stored in the "realname" column in that table.
How can I modify this query to capture all columns in "bugs," but perform a lookup on the assigned_to column and return usernames?
SELECT b.*, p.realname FROM bugs b
JOIN profiles p
ON b.assigned_to = p.userid