Select top 1 in group by sql server

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Author Topic

cnjsvision74 Starting Member

4 Posts

Posted - 2012-11-17 : 15:14:06

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I am new to SQL. I've inherited a report that needs modifying. I am looking to Select the TOP (1) value (DASHBOARD_STATUS_LEVEL) for each group (by MARKET_PROJECT) and place in an alias column (PROJECT_LEVEL). The SELECT statement below is a subquery that I've attempted that seems to just copy the DASHBOARD_STATUS_LEVEL into the PROJECT_LEVEL:

(SELECT TOP (1)SQL10.DASHBOARD_STATUS_LEVEL FROM dbo.OVP_CLAIM GROUP BY MARKET_PROJECT ORDER BY SQL10.DASHBOARD_STATUS_LEVEL DESC) AS PROJECT_LEVEL

MARKET_PROJECT, DASHBOARD_STATUS_LEVEL, PROJECT_LEVEL Austin T6-2011-03157, 3, 3 Austin T6-2011-03157, 3, 3 Austin T6-2011-03157, 3, 3 Austin T6-2011-03157, 2, 2 Austin T6-2011-03157, 1, 1 Austin T6-2011-03157, 1, 1 Austin T6-2012-03751, 1, 1 Austin T6-2012-04004, 1, 1 Austin T6-2012-04004, 1, 1 Austin T6-2012-04020, 3, 3 Austin T6-2012-04020, 2, 2 Austin T6-2012-04020, 1, 1 Austin T6-2012-04020, 1, 1 Austin T6-2012-04020, 1, 1 Austin T6-2012-04020, 1, 1 Austin T6-2012-04020, 1, 1

In other words, for each record with the same MARKET_PROJECT, the PROJECT_LEVEL should be the TOP (1) DASHBOARD_LEVEL. For Austin T6-2011-03157, each record in this group should have a PROJECT_LEVEL of 3.

**Initially, I wanted the PROJECT_LEVEL to represent the MAX(DASHBOARD_STATUS_LEVEL)for each group but received errors every time I used the MAX()function.

The SELECT TOP clause is useful on large tables with thousands of records. Returning a large number of records can impact performance.

Example

Select only the first 3 records of the Customers table:

SELECT TOP 3 * FROM Customers;

Try it Yourself »

Note: Not all database systems support the SELECT TOP clause. MySQL supports the LIMIT clause to select a limited number of records, while Oracle uses FETCH FIRST n ROWS ONLY and ROWNUM.

SQL Server / MS Access Syntax:

SELECT TOP number|percent columnname(s) FROM tablename WHERE condition;

MySQL Syntax:

SELECT columnname(s) FROM tablename WHERE condition LIMIT number;

Oracle 12 Syntax:

SELECT columnname(s) FROM tablename ORDER BY columnname(s) FETCH FIRST number ROWS ONLY;

Older Oracle Syntax:

SELECT columnname(s) FROM tablename WHERE ROWNUM <= number;

Older Oracle Syntax (with ORDER BY):

`SELECT TOP`0

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Demo Database

Below is a selection from the Customers table used in the examples:

CustomerID CustomerName ContactName Address City PostalCode Country 1 Alfreds Futterkiste Maria Anders Obere Str. 57 Berlin 12209 Germany 2 Ana Trujillo Emparedados y helados Ana Trujillo Avda. de la Constitución 2222 México D.F. 05021 Mexico 3 Antonio Moreno Taquería Antonio Moreno Mataderos 2312 México D.F. 05023 Mexico 4 Around the Horn Thomas Hardy 120 Hanover Sq. London WA1 1DP UK 5 Berglunds snabbköp Christina Berglund Berguvsvägen 8 Luleå S-958 22 Sweden

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LIMIT

The following SQL statement shows the equivalent example for MySQL:

Example

Select the first 3 records of the Customers table:

SELECT * FROM Customers LIMIT 3;

Try it Yourself »

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FETCH FIRST

The following SQL statement shows the equivalent example for Oracle:

Example

Select the first 3 records of the Customers table:

SELECT * FROM Customers FETCH FIRST 3 ROWS ONLY;

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SQL TOP PERCENT Example

The following SQL statement selects the first 50% of the records from the "Customers" table (for SQL Server/MS Access):

The following SQL statement shows the equivalent example for Oracle:

Example

SELECT * FROM Customers FETCH FIRST 50 PERCENT ROWS ONLY;

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ADD a WHERE CLAUSE

The following SQL statement selects the first three records from the "Customers" table, where the country is "Germany" (for SQL Server/MS Access):

The following SQL statement shows the equivalent example for MySQL:

The following SQL statement shows the equivalent example for Oracle:

Example

SELECT * FROM Customers WHERE Country='Germany' FETCH FIRST 3 ROWS ONLY;

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ADD the ORDER BY Keyword

Add the `SELECT TOP`1 keyword when you want to sort the result, and return the first 3 records of the sorted result.

How to get top 1 record in GROUP BY SQL Server?

In the outer query, you select all data from the CTE ( added_row_number ) and use a WHERE condition to specify which row to display from each group. Here, we want to display the first row, so the condition is row_number = 1 .

How to SELECT the first record in GROUP BY SQL?

We'll use the row_number() function partitioned by date in an inner query, and then filter to row_num = 1 in the outer query to get just the first record per group.

Can we use SELECT * with GROUP BY in SQL?

The GROUP BY syntax combines scalar column expressions and aggregate expressions. An asterisk (*) is allowed only in the COUNT(*) aggregate function. Following a scalar or aggregate expression, you can include the AS keyword followed by an alias.

How to use row_number with GROUP BY in SQL?

To group by row number in SQL, you can use a subquery or a common table expression (CTE). First, assign row numbers to each row using the ROW_NUMBER() function. Then, in the outer query, group the rows by their assigned row numbers.