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SQL AND OR

Compound conditions are made up of multiple simple conditions connected by AND or OR. There is no limit to the number of simple conditions that can be present in a single SQL statement.

The syntax for a compound condition is as follows:

SELECT "column_name"
FROM "table_name"

WHERE "simple condition"
{[AND|OR] "simple condition"}+

The {}+ means that the expression inside the bracket will occur one or more times. Note that AND and OR can be used interchangeably. In addition, we may use the parenthesis sign () to indicate the order of the condition.

For example, we may wish to select all stores with sales greater than $1,000 or all stores with sales less than $500 but greater than $275 in Table Store_Information,

Table Store_Information

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

we key in,

SELECT store_name
FROM Store_Information
WHERE Sales > 1000
OR (Sales < 500 AND Sales > 275)

Result:
store_name
Los Angeles
San Francisco

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"

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

For More Details: http://www.1keydata.com/sql/sqlwhere.html

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"

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