SQL Where

SQL Where

Next, we might want to conditionally select the data from a table. For example, we may want to only retrieve stores with sales above $1,000. To do this, we use the WHERE keyword. The syntax is as follows:


SELECT "column_name"
FROM "table_name"
WHERE "condition"

For example, to select all stores with sales above $1,000 in Table Store_Information,

Table:

Store_Information:

store_name--- Sales--- Date
Los Angeles ---$1500--- Jan-05-1999
San Diego--- $250 ---Jan-07-1999
Los Angeles--- $300--- Jan-08-1999
Boston--- $700 ---Jan-08-1999

we key in,


SELECT store_name
FROM Store_Information
WHERE Sales > 1000

Result:

store_name
Los Angeles

SELECT DISTINCT

The SELECT keyword allows us to grab all information from a column (or columns) on a table. This, of course, necessarily mean that there will be redundancies. What if we only want to select each DISTINCT element? This is easy to accomplish in SQL. All we need to do is to add DISTINCT after SELECT. The syntax is as follows:

SELECT DISTINCT "column_name"
FROM "table_name"

For example, to select all distinct stores in Table Store_Information,

Table

Store_Information
store_name---- Sales---- Date
Los Angeles ----$1500---- Jan-05-1999
San Diego ----$250---- Jan-07-1999
Los Angeles ----$300 ----Jan-08-1999
Boston ----$700---- Jan-08-1999



we key in,


SELECT DISTINCT store_name FROM Store_Information

Result:

store_name
Los Angeles
San Diego
Boston

SQL SELECT

SQL is short for Structured Query Language and is a widely used database language, providing means of data manipulation (store, retrieve, update, delete) and database creation.
Modern Relational Database Management Systems like MS SQL Server, Microsoft Access, MSDE, Oracle, DB2, Sybase, MySQL, Postgres and Informix use SQL as standard database language.
MS SQL Server specific version of the SQL is called T-SQL, Oracle version of SQL is called PL/SQL, MS Access version of SQL is called JET SQL.

A common use is to select data from the tables located in a database. Immediately, we see two keywords: we need to SELECT information FROM a table. (Note that a table is a container that resides in the database where the data is stored. For more information about how to manipulate tables, go to the Table Manipulation Section). Hence we have the most basic SQL structure:
SQL SELECT
SELECT "column_name" FROM "table_name"

To illustrate the above example, assume that we have the following table:

Table
Store_Information.
.

store_name ----- Sales ----- Date
Los Angeles ----- $1500----- Jan-05-1999
San Diego ----- $250 ----- Jan-07-1999
Los Angeles ----- $300 ----- Jan-08-1999
Boston ----- $700----- Jan-08-1999

We shall use this table as an example throughout the tutorial (this table will appear in all sections). To select all the stores in this table, we key in,

SELECT store_name FROM Store_Information

Result:

store_name
Los Angeles
San Diego
Los Angeles
Boston

Multiple column names can be selected, as well as multiple table names