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SQL SELECT

The SQL Select Statement:

Microsoft Access is a Visual Basic based application that allows the SQL statements to be embedded in VBA code and macros. One of the most used SQL statements, the SELECT statement, provides the much needed flexibility in the retrieval of data from a database. The general form of the SELECT command is:

SELECT select_list FROM source
[ WHERE condition(s) ] 
[ GROUP BY expression ]
[ HAVING condition ]
[ ORDER BY expression ] ;
  • The SELECT statement indicates that you which to query and retrieve information from a database. The select_list specifies the type of information (or column names) to retrieve. The keyword ALL or the wildcard character asterisk (*) could be used to signify all columns in the database. Also, the keyword DISTINCT could be used to discard duplicate records and retrieve only the unique records for the specified columns.
  • The FROM clause is the only required clause in the SELECT statement. The FROM clause specifies the specific database tables to retrieve data from.
  • The WHERE clause limits the results to those records (or rows) that meet some particular conditions (optional).
  • The GROUP BY clause specifies the format of the output. The expression specifies a column listing such that all rows contained in the specified columns will be aggregated together (optional).
  • The HAVING clause specifies the specific conditions to group by (optional).
  • The ORDER BY clause specifies whether to output the query result in ascending or descending order. The expression specifies a column listing to order by (optional).

The select statement, like all other SQL statements, should end with a semi-colon. The semi-colon terminates a statement. If you wanted to select an entire table, every record and every field, the command would be:

SELECT * FROM source;
 
or


SELECT ALL FROM source;

The absence of the WHERE clause signifies that there are no restrictions to be placed on the rows, so display all rows. This query statement can be further modified to indicate specific fields (or columns) and specific records (or rows) to retrieve, and also set limitations on, the queried results using the WHERE clause. The absence of the GROUP BY, HAVING and ORDER BY clauses signifies that there are no particulars restrictions to be put on the output of the query.

The optional conditions may make use of comparison operators, which include the following:

COMPARISON OPERATORS
= Equal To
> Greater Than
< Less Than
>= Greater Than or Equal To
<= Less Than or Equal To
<> Not Equal To
LIKE String Comparison Test

Aggregate functions can be included to perform computations on numeric values. Aggregate functions include the following:

AGGREGATE FUNCTIONS
MIN Returns the smallest value in a given column
MAX Returns the largest value in a given column
SUM Returns the sum of the numeric values in a given column
AVG Returns the average value of a given column
COUNT Returns the total number of values in a given column
COUNT(*) Returns the number of rows in a table