SELECT statement

Retrieves rows from the database and enables the selection of one or many rows or columns from one or many tables. The full syntax of the SELECT statement is complex, but the main clauses can be summarized as:

SELECT *select_list* [ INTO *new_table* ]
[ FROM *table_source* ] [ WHERE *search_condition* ]
[ GROUP BY *group_by_expression* ]
[ HAVING *search_condition* ]
[ ORDER BY *order_expression* [ ASC | DESC ] ]

The UNION, EXCEPT, and INTERSECT operators can be used between queries to combine or compare their results
into one result set.

Syntax

<SELECT statement> ::=
<query_expression>
[ ORDER BY { order_by_expression | column_position [ ASC | DESC ] }
[ ,...n ] ]
[ <FOR Clause>]
[ OPTION ( <query_hint> [ ,...n ] ) ]
<query_expression> ::=
    { <query_specification> | ( <query_expression> ) }
    [  { UNION [ ALL ] | EXCEPT | INTERSECT }
        <query_specification> | ( <query_expression> ) [...n ] ]
<query_specification> ::=
SELECT [ ALL | DISTINCT ]
    [TOP ( expression ) [PERCENT] [ WITH TIES ] ]
    <select_list>
    [ INTO new_table ]
    [ FROM { <table_source> } [ ,...n ] ]
    [ WHERE <search_condition> ]
    [ <GROUP BY> ]
    [ HAVING <search_condition> ]

Remarks

Because of the complexity of the SELECT statement, detailed syntax elements and arguments are shown by clause:

  • SELECT Clause

  • UNION

  • INTO Clause

  • EXCEPT and INTERSECT

  • FROM

  • ORDER BY

  • WHERE

  • GROUP BY

  • OPTION Clause

The order of the clauses in the SELECT statement is significant. Any one of the optional clauses can be omitted, but when the optional clauses are used, they must appear in the appropriate order.

SELECT statements are permitted in user-defined functions only if the select lists of these statements contain expressions that assign values to variables that are local to the functions.

A four-part name can be used as a table source wherever a table name can appear in a SELECT statement.

Logical Processing Order of the SELECT statement

The following steps show the logical processing order, or binding order, for a SELECT statement. This order determines when the objects defined in one step are made available to the clauses in subsequent steps. For example, if the query processor can bind to (access) the tables or views defined in the FROM clause, these objects and their columns are made available to all subsequent steps. Conversely, because the SELECT clause is step 8, any column aliases or derived columns defined in that clause cannot be referenced by preceding clauses. However, they can be referenced by subsequent clauses such as the ORDER BY clause. The actual physical execution of the statement is determined by the query processor and the order may vary from this list.

  1. FROM

  2. ON

  3. JOIN

  4. WHERE

  5. GROUP BY

  6. WITH CUBE or WITH ROLLUP

  7. HAVING

  8. SELECT

  9. DISTINCT

  10. ORDER BY

  11. TOP

Warning

The preceding sequence is usually true. However, there are uncommon cases where the sequence may differ.

For example, suppose you have a clustered index on a view, and the view excludes some table rows, and the view’s SELECT column list uses a CONVERT that changes a data type from varchar to integer. In this situation, the CONVERT may execute before the WHERE clause executes. Uncommon indeed. Often there is a way to modify your view to avoid the different sequence, if it matters in your case.

Permissions

Selecting data requires SELECT permission on the table or view, which could be inherited from a higher scope such as SELECT permission on the schema or CONTROL permission on the table. Or requires membership in the db_datareader or db_owner fixed database roles, or the sysadmin fixed server role. Creating a new table using SELECT INTO also requires both the CREATE TABLE permission, and the ALTER SCHEMA permission on the schema that owns the new table.

Examples

The following examples use the AdventureWorksDW2012 database.

A. Using SELECT to retrieve rows and columns

This section shows three code examples. This first code example returns all rows (no WHERE clause is specified) and all columns (using the *) from the DimEmployee table.

SELECT *
  FROM DimEmployee
 ORDER BY LastName;

This next example using table aliasing to achieve the same result.

SELECT e.*
  FROM DimEmployee AS e
 ORDER BY LastName;

This example returns all rows (no WHERE clause is specified) and a subset of the columns (FirstName, LastName, StartDate) from the DimEmployee table in the AdventureWorksPDW2012 database. The third column heading is renamed to FirstDay.

SELECT FirstName, LastName, StartDate AS FirstDay
  FROM DimEmployee
 ORDER BY LastName;

This example returns only the rows for DimEmployee that have an EndDate that is not NULL and a MaritalStatus of ‘M’ (married).

SELECT FirstName, LastName, StartDate AS FirstDay
  FROM DimEmployee
 WHERE EndDate IS NOT NULL
   AND MaritalStatus = 'M'
 ORDER BY LastName;

B. Using SELECT with column headings and calculations

The following example returns all rows from the DimEmployee table, and calculates the gross pay for each employee based on their BaseRate and a 40-hour work week.

SELECT FirstName
     , LastName
     , BaseRate
     , BaseRate * 40 AS GrossPay
  FROM DimEmployee
 ORDER BY LastName;

C. Using DISTINCT with SELECT

The following example uses DISTINCT to generate a list of all unique titles in the DimEmployee table.

SELECT DISTINCT Title
  FROM DimEmployee
 ORDER BY Title;

D. Using GROUP BY

The following example finds the total amount for all sales on each day.

SELECT OrderDateKey, SUM(SalesAmount) AS TotalSales
  FROM FactInternetSales
 GROUP BY OrderDateKey
 ORDER BY OrderDateKey;

Because of the GROUP BY clause, only one row containing the sum of all sales is returned for each day.

E. Using GROUP BY with multiple groups

The following example finds the average price and the sum of Internet sales for each day, grouped by order date and the promotion key.

SELECT OrderDateKey
     , PromotionKey
     , AVG(SalesAmount) AS AvgSales
     , SUM(SalesAmount) AS TotalSales
  FROM FactInternetSales
 GROUP BY OrderDateKey, PromotionKey
 ORDER BY OrderDateKey;

F. Using GROUP BY and WHERE

The following example puts the results into groups after retrieving only the rows with order dates later than August 1, 2002.

SELECT OrderDateKey, SUM(SalesAmount) AS TotalSales
  FROM FactInternetSales
 WHERE OrderDateKey > '20020801'
 GROUP BY OrderDateKey
 ORDER BY OrderDateKey;

G. Using GROUP BY with an expression

The following example groups by an expression. You can group by an expression if the expression does not include aggregate functions.

SELECT SUM(SalesAmount) AS TotalSales
  FROM FactInternetSales
 GROUP BY (OrderDateKey * 10);

H. Using GROUP BY with ORDER BY

The following example finds the sum of sales per day, and orders by the day.

SELECT OrderDateKey
     , SUM(SalesAmount) AS TotalSales
  FROM FactInternetSales
 GROUP BY OrderDateKey
 ORDER BY OrderDateKey;

I. Using the HAVING clause

This query uses the HAVING clause to restrict results.

SELECT OrderDateKey
     , SUM(SalesAmount) AS TotalSales
  FROM FactInternetSales
 GROUP BY OrderDateKey
HAVING OrderDateKey > 20010000
 ORDER BY OrderDateKey;

See Also