WHERE in the database is.....?

If a WHERE clause is included with SELECT and FROM we introduce a search condition. Only those rows (all) that satisfy the condition are returned in the result.

SELECT staff_no
FROM staff
WHERE name = 'Banner';        //name is data type string

Points:

• The WHERE clause uses a single predicate that evaluates to true or false.
• The referenced column is not returned but could be if so desired.
• Character strings are contained in single quotes.
• Uppercase and lowercase characters are not distinguished from one another. BANNER is the same as banner.

The logical processing follows the path specified below:

• FROM clause produces intermediate table, a copy of the staff table.
• WHERE clause produces a second intermediate table (via horizontal slicing and checking for true/false for each row against the predicate), with copies of all rows in the first intermediate table that satisfy the condition.
• SELECT takes the specified column from the second intermediate table to produce the final table.
• Aggregate functions are not allowed in the WHERE clause.

Comments, suggestions, ideas to
Stuart Banner