I have a SQL Server database on my computer, and there are two tables in it.
This is the first one:
SELECT
[ParticipantID]
,[ParticipantName]
,[ParticipantNumber]
,[PhoneNumber]
,[Mobile]
,[Email]
,[Address]
,[Notes]
,[IsDeleted]
,[Gender]
,[DOB]
FROM
[Gym].[dbo].[Participant]
and this is the second one
SELECT
[ParticipationID]
,[ParticipationNumber]
,[ParticpationTypeID]
,[AddedByEmployeeID]
,[AddDate]
,[ParticipantID]
,[TrainerID]
,[ParticipationDate]
,[EndDate]
,[Fees]
,[PaidFees]
,[RemainingFees]
,[IsPeriodParticipation]
,[NoOfVisits]
,[Notes]
,[IsDeleted]
FROM
[Gym].[dbo].[Participation]
Now I need to write a T-SQL query that can return
SELECT
Participant.ParticipantNumber,
Participation.ParticipationDate,
Participation.EndDate
FROM
Participation
WHERE
Participant.ParticipantID = Participation.ParticipantID;
and I'm going to be thankful
SQL Server performs sort, intersect, union, and difference operations using in-memory sorting and hash join technology. Using this type of query plan, SQL Server supports vertical table partitioning, sometimes called columnar storage.
SQL Server employs three types of join operations:
Nested Loops joins
Merge joins
Hash joins
Join Fundamentals
By using joins, you can retrieve data from two or more tables based on logical relationships between the tables. Joins indicate how Microsoft SQL Server should use data from one table to select the rows in another table.
A join condition defines the way two tables are related in a query by:
Specifying the column from each table to be used for the join. A typical join condition specifies a foreign key from one table and its associated key in the other table.
Specifying a logical operator (for example, = or <>,) to be used in comparing values from the columns.
Inner joins can be specified in either the FROM or WHERE clauses. Outer joins can be specified in the FROM clause only. The join conditions combine with the WHERE and HAVING search conditions to control the rows that are selected from the base tables referenced in the FROM clause.
Follow this link to help you understand joins better in mssql:
link to joins
Related
My application access data from a table in SQL Server. Consider the table name is PurchaseDetail with some other columns.
The select query has below where clauses.
1. name - name has 10000 values only.
2. createdDateTime
The actual query is
select *
from PurchaseDetail
where name in (~2000 name)
and createdDateTime = 'someDateValue';
The SQL tuning advisor gave some recommendation. I tried with those recommended indexes. The performance increased a bit but not completely.
Is there any wrong in my query? or Is there any possible to change/improve my select query?
Because I didn't use IN in where clause before. My table having more than 100 million records.
Any suggestion please?
In this case using IN for that much data is not good at all.
this best way is to use INNER JOIN instead.
It would be nicer if insert those names into a temp table and INNER JOIN it with your SELECT query.
This question already has answers here:
Explicit vs implicit SQL joins
(12 answers)
Closed 7 years ago.
I am on a project where much of the queries are performed by including multiple tables in the FROM clause. I know this is legal, but I have always used explicit JOINs instead.
For example, two tables (using SQL Server DDL)
CREATE TABLE Manufacturers(
ManufacturerID INT IDENTITY(1,1) PRIMARY KEY NOT NULL,
Name varchar(100))
CREATE TABLE Cars (
ModelID INT IDENTITY(1,1) PRIMARY KEY NOT NULL,
ManufacturerID INT CONSTRAINT FOREIGN KEY FK_Manufacturer REFERENCES Manufacturers(ManufacturerID),
ModelName VARCHAR(100))
If I want to find the models for GM, I could do either:
SELECT ModelName FROM Cars c, Manufacturers m WHERE c.ManufacturerID=m.ManufacturerID AND m.Name='General Motors'
or
SELECT ModelName FROM Cars c INNER JOIN Manufacturers m ON c.ManufacturerID=m.ManufacturerID WHERE m.Name='General Motors'
My question is this: does one form perform better than the other? Aside from how the tables are defined in Oracle vs SQL Server, does one form of join work better than the other in Oracle or SQL Server? What if you include more tables, say 3 or 4? Does that change the performance characteristics, assuming the queries are constructed to return an equivalent record set?
My question is this: does one form perform better than the other?
They should not. You can check your execution plans to be certain, but every RDBMS I've worked with generates the same plans for comma (ANSI-89) joins as they do for ANSI-92 explicit joins. (Note that comma joins didn't stop being ANSI SQL, it's just that ANSI-92 is where the explicit syntax first appeared.)
Aside from how the tables are defined in Oracle vs SQL Server, does one form of join work better than the other in Oracle or SQL Server?
As far as the server is concerned, no.
What if you include more tables, say 3 or 4? Does that change the performance characteristics, assuming the queries are constructed to return an equivalent record set?
It's possible. With comma joins, I'm not sure it's possible to control the JOIN order with parentheses like you can with explicit joins:
SELECT *
FROM Table1 t1
INNER JOIN (
Table2 t2
INNER JOIN Table3 t3
t2.id = t3.id)
ON t1.id = t2.id
This can affect overall query performance (for better or worse). I'm not sure how to accomplish the same level of control with comma joins, but I've never fully learned comma join syntax. I don't know if you can say Table1 t1, (Table2 t2, Table3 t3), but I don't believe you can. I think you'd have to use subqueries to do that.
The primary advantages of explicit joins are:
Easier to read. It makes it very clear which conditions are used with which join. You won't ever see Table1 t1, Table2 t2, Table3 t3 and then have to dig into the WHERE clause to figure out if one of those joins is an outer join. It also means the WHERE clause isn't stuffed full of all these join conditions you know you don't care about changing when you modify a query.
Easier to use outer joins. In the case of outer joins, you can even specify literal filter values in the outer table without having to handle nulls from the outer join.
Easier to reuse existing joins. If you just want to query from the same relations, you can just grab the FROM clause. You don't have to worry about what bits from the WHERE clause you want and what bits you don't.
Identical syntax across RDBMSs. When you spend all day switching between Oracle and SQL Server, the last thing you want to worry about is confusing + and *= to get your outer joins right.
All of the above make the explicit join syntax more maintainable, which is a very important factor for software.
I have two tables arts and artsdetails.. artsId is the primary key in arts table foreign key in artdetails table. I am selecting values from both table but my query is giving error as
"Invalid object name 'artdetails'"
My query is:
SELECT arts.artsId, artdetails.mainImage
FROM artdetails
INNER JOIN arts ON artdetails.artsId = arts.artsId;
Please help.
You're probably not running the query in the database where these tables live.
If you're using SQL Server Management studio, look in the top left for a drop down containing the database names. It probably says 'master' (as that's the default). Select the one containing the tables you're using and re-run your query.
Failing that, check they're both running in the same schema as Tom suggests.
You can fully quality table names in your query like this:
SELECT a.artsId, ads.mainImage
FROM [DBNAME].[SCHEMA].artdetails ad
INNER JOIN [DBNAME].[SCHEMA].arts a ON ad.artsId = a.artsId;
Also using table abbreviations tidies things up a bit.
I have two tables CountryMaster and StatesMaster. The fields are:
CountryMaster(CountryId, Name)
StateMaster(StateId, Name, CountryId)
The StateMaster.CountryId is a Foreign key. I want to get the Name of States from StateMaster as well as the Name of the Country to which that State belongs from CountryMaster.
I want this in one query.
How can i get this?
SELECT
s.Name AS StateName
, c.Name AS CountryName
FROM
dbo.StateMaster s
INNER JOIN
dbo.CountryMaster c
ON c.CountryId = s.CountryId
Join Fundamentals
By using joins, you can retrieve data from two or more tables based on
logical relationships between the tables. Joins indicate how Microsoft
SQL Server should use data from one table to select the rows in
another table.
A join condition defines the way two tables are related in a query by:
Specifying the column from each table to be used for the join. A
typical join condition specifies a foreign key from one table and its
associated key in the other table.
Specifying a logical operator (for example, = or <>,) to be used
in comparing values from the columns.
Inner joins can be specified in either the FROM or WHERE clauses.
Outer joins can be specified in the FROM clause only. The join
conditions combine with the WHERE and HAVING search conditions to
control the rows that are selected from the base tables referenced in
the FROM clause.
I have written a table-valued UDF that starts by a CTE to return a subset of the rows from a large table.
There are several joins in the CTE. A couple of inner and one left join to other tables, which don't contain a lot of rows.
The CTE has a where clause that returns the rows within a date range, in order to return only the rows needed.
I'm then referencing this CTE in 4 self left joins, in order to build subtotals using different criterias.
The query is quite complex but here is a simplified pseudo-version of it
WITH DataCTE as
(
SELECT [columns] FROM table
INNER JOIN table2
ON [...]
INNER JOIN table3
ON [...]
LEFT JOIN table3
ON [...]
)
SELECT [aggregates_columns of each subset] FROM DataCTE Main
LEFT JOIN DataCTE BananasSubset
ON [...]
AND Product = 'Bananas'
AND Quality = 100
LEFT JOIN DataCTE DamagedBananasSubset
ON [...]
AND Product = 'Bananas'
AND Quality < 20
LEFT JOIN DataCTE MangosSubset
ON [...]
GROUP BY [
I have the feeling that SQL Server gets confused and calls the CTE for each self join, which seems confirmed by looking at the execution plan, although I confess not being an expert at reading those.
I would have assumed SQL Server to be smart enough to only perform the data retrieval from the CTE only once, rather than do it several times.
I have tried the same approach but rather than using a CTE to get the subset of the data, I used the same select query as in the CTE, but made it output to a temp table instead.
The version referring the CTE version takes 40 seconds. The version referring the temp table takes between 1 and 2 seconds.
Why isn't SQL Server smart enough to keep the CTE results in memory?
I like CTEs, especially in this case as my UDF is a table-valued one, so it allowed me to keep everything in a single statement.
To use a temp table, I would need to write a multi-statement table valued UDF, which I find a slightly less elegant solution.
Did some of you had this kind of performance issues with CTE, and if so, how did you get them sorted?
Thanks,
Kharlos
I believe that CTE results are retrieved every time. With a temp table the results are stored until it is dropped. This would seem to explain the performance gains you saw when you switched to a temp table.
Another benefit is that you can create indexes on a temporary table which you can't do to a cte. Not sure if there would be a benefit in your situation but it's good to know.
Related reading:
Which are more performant, CTE or temporary tables?
SQL 2005 CTE vs TEMP table Performance when used in joins of other tables
http://msdn.microsoft.com/en-us/magazine/cc163346.aspx#S3
Quote from the last link:
The CTE's underlying query will be
called each time it is referenced in
the immediately following query.
I'd say go with the temp table. Unfortunately elegant isn't always the best solution.
UPDATE:
Hmmm that makes things more difficult. It's hard for me to say with out looking at your whole environment.
Some thoughts:
can you use a stored procedure instead of a UDF (instead, not from within)?
This may not be possible but if you can remove the left join from you CTE you could move that into an indexed view. If you are able to do this you may see performance gains over even the temp table.