This my scenario I tried to search a record in the SQL table using the name. So, I tried to create a subquery and I used like operator also in Postgres. SQL query It's working fine. but it's taking so much time. So, I checked why it's taking so much time. the reason is the subquery. In the subquery it hitting all the records in the table. How to optimize subquery.
SQL QUery
SELECT
id, latitude,longitude,first_name,last_name,
contact_company_id,address,address2,city,state_id, zip,country_id,default_phone_id,last_contacted,image,contact_type_id
FROM contact
WHERE company_id = 001
AND contact_company_id IN (select id from contactcompany where lower( name ) ~*'jack')
So, I tried to run this query it's taking 2 seconds and it hit all records in the contact company table that only It's takes time.
How to optimize subquery using SQL?
Please try a sub query as a inner join with a main table, both query give same result.
Example here :
SELECT contact.id,
contact.latitude,
contact.longitude,
contact.first_name,
contact.last_name,
contact.contact_company_id,
contact.address,
contact.address2,
contact.city,
contact.state_id,
contact.zip,
contact.country_id,
contact.default_phone_id,
contact.last_contacted,
contact.image,
contact.contact_type_id
FROM contact As contact
Inner Join contactcompany As contactcompany On contactcompany.id = contact_company_id
WHERE company_id = 001
AND lower( name ) ~*'jack'
I would start by writing the query using exists. Then, company_id is either a string or a number. Let met guess that it is a string, because the constant is represented with leading zeros. If so, use single quotes:
SELECT c.*
FROM contact c
WHERE company_id = '001' AND
EXISTS (SELECT 1
FROM contactcompany cc
WHERE cc.name ~* 'jack' AND
cc.id = c.contact_company_id
);
Then an index on contact(compnay_id, contact_company_id) makes sense. And for the subquery, contactcompany(id, name).
There may be other alternatives for writing the query, but your question has not provided much information on table sizes, current performance, or the data types.
Related
From this question
Write a select query for getting table value using another table field value
I tried this query
select guardian_nm,guardian_age
from guardian
where stu_uid IN (
select stu_uid from student where stu_id=1 order by timestamp desc limit 1)
But getting the following error
Error code is -4743 ATTEMPT TO USE A FUNCTION WHEN THE APPLICATION
COMPATIBILITY SETTING IS SET FOR A PREVIOUS LEVEL
Can anyone help me please ?
You are using limit 1 so stu_uid you can write it =.
And I will suggest do not use reserved MYSQL words in column names like timestamp,
Use join instead of subquery.
The advantage of a join includes that it executes faster. The
retrieval time of the query using joins almost always will be faster
than that of a subquery. By using joins, you can maximize the
calculation burden on the database i.e., instead of multiple queries
using one join query.
Try:
select guardian_nm,guardian_age,
from guardian
inner join
student
on guardian.stu_uid=student.stu_uid
where student.stu_id=1
order by timestamp desc limit 1 ;
Working demo: http://sqlfiddle.com/#!9/923c30/3
I have two tables (PlayerDTO and ClubDTO) and am using a JOIN to fetch data as follows:
SELECT * FROM PlayerDTO AS pl
INNER JOIN ClubDTO AS cl
ON pl.currentClub = cl.id
WHERE cl.nation = 7
This returns the correct rows from PlayerDTO, but in every row the id column has been changed to the value of the currentClub column (eg instead of pl.id 3,456 | pl.currentClub 97, it has become pl.id 97 | pl.currentClub 97).
So I tried the query listing all the columns by name instead of Select *:
SELECT pl.id, pl.nationality, pl.currentClub, pl.status, pl.lastName FROM PlayerDTO AS pl
INNER JOIN ClubDTO AS cl
ON pl.currentClub = cl.id
WHERE cl.nation = 7
This works correctly and doesn’t change any values.
PlayerDTO has over 100 columns (I didn’t list them all above for brevity, but I included them all in the query) but obviously I don’t want to write every column name in every query.
So could somebody please explain why Select * changes the id value and what I need to do to make it work correctly? All my tables have a column called id, is that something to do with it?
SELECT *... is, according to the docs...
shorthand for “select all columns.” (Source: Dev.MySQL.com
Both your tables have id columns, so which should be returned? It's not indicated, so MySQL makes a guess. So select what you want to select...
SELECT pl.id, *otherfieldsyouwant* FROM PlayerDTO AS pl...
Or...
SELECT pl.* FROM PlayerDTO AS pl...
Typically, SELECT * is bad form. The odds you are using every field is astronomically low. And the more data you pull, the slower it is.
I just registered and want to ask.
I learn sql queries not so long time and I got a trouble when I decided to move a table to another database. A few articles were read about building long subqueries , but they didn't help me.
Everything works perfect before that my action.
I just moved the table and tried to rewrite the query while whole day.
update [dbo].Full
set [salary] = 1000
where [dbo].Full.id in (
select distinct k1.id
from (
select id, Topic, User
from Full
where User not in (select distinct topic_name from [DB_1].dbo.S_School)
) k1
where k1.id not in (
select distinct k2.id
from (
select id, Topic, User
from Full
where User not in (select distinct topic_name from [DB_1].dbo.Shool)
) k2,
List_School t3
where charindex (t3.NameApp, k2.Topic)>5
)
)
I moved table List_School to database [DB_1] and I can't to bend with it.
I can't write [DB_1].dbo.List_School. Should I use one more subquery?
I even thought about create a few temporary tables but it can influence on speed of execution.
Sql gurus , please invest some your time on me. Thank you in advance.
I will be happy for each hint, which you give me.
There appear to be a number of issues. You are comparing the user column to the topic_name column. An expected meaning of those column names would suggest you are not comparing the correct columns. But that is a guess.
In the final subquery you have an ansi join on table List_School but no join columns which means the join witk k2 is a cartesian product (aka cross join) which is not what you would want in most situations. Again a guess as no details of actual problem data or error messages was provided.
SELECT
c.ConfigurationID AS RealflowID, c.companyname,
c.companyphone, c.ContactEmail, COUNT(k.caseid)
FROM
dbo.Configuration c
INNER JOIN
dbo.cases k ON k.SiteID = c.ConfigurationId
WHERE
EXISTS (SELECT * FROM dbo.RepairEstimates
WHERE caseid = k.caseid)
AND c.AccountStatus = 'Active'
AND c.domainid = 46
GROUP BY
c.configurationid,c.companyname, c.companyphone, c.ContactEmail
I have this query - I am using the configuration table to get the siteid of the cases in the cases table. And if the case exists in the repair estimates table pull the company details listed and get a count of how many cases are in the repair estimator table for that siteid.
I hope that is clear enough of a description.
But the issue here is the count is not correct with the data that is being pulled. Is there something I could do differently? Different join? Remove the exists add another join? I am not sure I have tried many different things.
Realized I was using the wrong table. The query was correct.
I just hit a wall with my SQL query fetching data from my MS SQL Server.
To simplify, say i have one table for sales, and one table for customers. They each have a corresponding userId which i can use to join the tables.
I wish to first SELECT from the sales table where say price is equal to 10, and then join it on the userId, in order to get access to the name and address etc. from the customer table.
In which order should i structure the query? Do i need some sort of subquery or what do i do?
I have tried something like this
SELECT *
FROM Sales
WHERE price = 10
INNER JOIN Customers
ON Sales.userId = Customers.userId;
Needless to say this is very simplified and not my database schema, yet it explains my problem simply.
Any suggestions ? I am at a loss here.
A SELECT has a certain order of its components
In the simple form this is:
What do I select: column list
From where: table name and joined tables
Are there filters: WHERE
How to sort: ORDER BY
So: most likely it was enough to change your statement to
SELECT *
FROM Sales
INNER JOIN Customers ON Sales.userId = Customers.userId
WHERE price = 10;
The WHERE clause must follow the joins:
SELECT * FROM Sales
INNER JOIN Customers
ON Sales.userId = Customers.userId
WHERE price = 10
This is simply the way SQL syntax works. You seem to be trying to put the clauses in the order that you think they should be applied, but SQL is a declarative languages, not a procedural one - you are defining what you want to occur, not how it will be done.
You could also write the same thing like this:
SELECT * FROM (
SELECT * FROM Sales WHERE price = 10
) AS filteredSales
INNER JOIN Customers
ON filteredSales.userId = Customers.userId
This may seem like it indicates a different order for the operations to occur, but it is logically identical to the first query, and in either case, the database engine may determine to do the join and filtering operations in either order, as long as the result is identical.
Sounds fine to me, did you run the query and check?
SELECT s.*, c.*
FROM Sales s
INNER JOIN Customers c
ON s.userId = c.userId;
WHERE s.price = 10