The SELECT statement is the most frequently used Transact-SQL statement. We use the SELECT statement for the following purposes:

We often see SELECT statements within programming objects (such as views, stored procedures, functions, batches, and common table expressions (CTEs)). We also use SELECT statements to run ad hoc queries, most often through an SSMS 2014 query window. The SELECT statement has several clauses, most of which are optional. The following is the general syntax of the SELECT statement:

SELECT [TOP(n)|TOP(n) PERCENT] [ALL|DISTINCT] select_list
[INTO[[database.]owner.]table_name]
FROM[[[database.]owner.]table_name|view_name|UDF]
[WHERE search_conditions]
[GROUP BY aggregate_free_expression]
[HAVING search_conditions]
[ORDER BY table_or_view_and_column]
[COMPUTE row_aggregate(column_name)]
[BY column_name]]
[FOR for_options]
[OPTION (query_hint)][;]

The select_list parameter is the list of expressions (such as numeric computation, constants, functions, aliases, and subqueries) or columns in the SELECT clause that you want to return in the query result set. We can use asterisk (*) as a wildcard character in the select_list parameter of the SELECT statement to return all columns from the selected tables. For example, the following query returns all columns from the Sales.Currency table in the AdventureWorks2012 database:

SELECT  *
FROM    [Sales].[Currency];

However, you should avoid using the asterisk (*) wildcard character in select_list; instead, provide a full list of columns needed for the query, because SQL Server resolves the column list each time the SELECT statement is executed. Moreover, if we use SELECT * in the T-SQL code, the SELECT statement might generate an error due to changes in the schemas of the underlying tables. To display the values in CurrencyCode and Name from the Sales.Currency table, run the following code:

SELECT  [CurrencyCode] ,
        [Name]
FROM    [Sales].[Currency];

The purpose of the FROM clause in the SELECT statement is to identify the data sources for a query. For example, in the previous example, we used the FROM clause in the SELECT statement to specify the Sales.Currency table as a data source for the query.

The WHERE clause is used to specify the query criteria, so that only the required subset of data is returned in the result set. For example, suppose that you want to write a query to return all the currency codes that begin with the A character. To accomplish this, we include the WHERE clause in the preceding query as follows:

SELECT  [CurrencyCode] ,
        [Name]
FROM    [Sales].[Currency]
WHERE   [CurrencyCode] LIKE 'A%';

The WHERE clause always comes after the FROM clause and can include conditions that use the following: