Sunday, April 14, 2013

SELECT Statement

SELECT Statement

The SELECT statement is used to query the database and retrieve selected data that match the criteria that you specify.
The SELECT statement has five main clauses to choose from, although, FROM is the only required clause. Each of the clauses have a vast selection of options, parameters, etc.

 Here is the format of the SELECT statement:

SELECT [ALL | DISTINCT] column1[,column2] FROM table1[,table2] [WHERE "conditions"] [GROUP BY "column-list"] [HAVING "conditions] [ORDER BY "column-list" [ASC | DESC] ] 

FROM & WHERE clause quick review

SELECT name, age, salary FROM employee WHERE age > 50;
The above statement will select all of the values in the name, age, and salary columns from the employee table whose age is greater than 50.
Note: Remember to put a semicolon at the end of your SQL statements. The ; indicates that your SQL statment is complete and is ready to be interpreted.
Comparison Operators
= Equal
> Greater than
< Less than
>= Greater than or equal to
<= Less than or equal to
<> or != Not equal to
LIKE String comparison test

*Note about LIKE
SELECT name, title, dept FROM employee WHERE title LIKE 'Pro%'; 

The above statement will select all of the rows/values in the name, title, and dept columns from the employee table whose title starts with 'Pro'. This may return job titles including Programmer or Pro-wrestler.
ALL and DISTINCT are keywords used to select either ALL (default) or the "distinct" or unique records in your query results. If you would like to retrieve just the unique records in specified columns, you can use the "DISTINCT" keyword. DISTINCT will discard the duplicate records for the columns you specified after the
"SELECT" statement: For example:
SELECT DISTINCT age FROM employee_info;
This statement will return all of the unique ages in the employee_info table.
ALL will display "all" of the specified columns including all of the duplicates. The ALL keyword is the default if nothing is specified.

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