Advanced Select Statements

Select List Variations SELECT *SELECT * Column NamingColumn Naming Arithmetic ExpressionsArithmetic Expressions ConstantsConstants StringsStrings

Column Naming Using column aliases we can control how the column names are displayed in our output. SELECT au_fname First_Name FROM authors The output will reflect this column name. First_Name JoeDanSue

Expressions Arithmetic expressions can be used in the select list of a SELECT statement. Column (+-*/) ColumnColumn (+-*/) Column eg. Unit_cost * items_soldeg. Unit_cost * items_sold Constant (+-*/) ColumnConstant (+-*/) Column eg. Unit_cost * 1.1eg. Unit_cost * 1.1 ConstantConstant FunctionsFunctions eg. Avg(sales)eg. Avg(sales)

Expressions allow us... To make projections To do “What if” analyses Alter reported data without altering the physical data

Precedence Hierarchy of Arithmetic Operators Parentheses Multiplication, Division Addition, Subtraction (2+2*3)/4 = 2

The Where Clause Arithmetic (+-*/) /Comparative (> <=,!=) Operators WHERE cost * 2 >= 20 WHERE state != ‘CA’ Logical Operators (AND, OR, NOT)Logical Operators (AND, OR, NOT) Ranges (BETWEEN, NOT BETWEEN)Ranges (BETWEEN, NOT BETWEEN) Lists (IN, NOT IN)Lists (IN, NOT IN) WHERE state NOT IN (‘CA’, ‘MD’, ‘NJ’) Unknowns (IS NULL, IS NOT NULL)Unknowns (IS NULL, IS NOT NULL) Character Matches (LIKE, NOT LIKE)Character Matches (LIKE, NOT LIKE) WHERE au_lname LIKE (‘Gr%’) OR au_lname LIKE (‘_reen’)

Precedence Hierarchy of Logical Operators Parentheses Multiplication, Division Addition, Subtraction NOT AND OR

Lists Can save a lot of typing! Can use a list or a sub query List example: Select au_lname, au_fname from authors where state in (‘CA’, ‘IN’, ‘MD’) SubQuery Example: Select pub_name from publishers where pub_id in (select pub_id from titles where total_sales > 3000)

Character Matches % - 0 or more character% - 0 or more character _ - 1 character_ lets you escape a - lets you escape a wildcard You can use 1 or more wildcards in a string.You can use 1 or more wildcards in a string. Eg. I%a = Indiana, Iowa, Ina-goda-da-vida

Things to Remember Logical operators can only be used with the WHERE clauseLogical operators can only be used with the WHERE clause The wildcards % and _ can only be used with LIKE and NOT LIKEThe wildcards % and _ can only be used with LIKE and NOT LIKE Wildcards can be used before and after the search string.Wildcards can be used before and after the search string. Strings must be quotedStrings must be quoted NULL is not the same as zeroNULL is not the same as zero

Aggregate Functions SUM ([DISTINCT] expr) The total sum of values in expression AVG ([DISTINCT] expr) The average of values in the expression COUNT ([DISTINCT] expr) The number of non-null values in the expression MAX (expr) The highest value in the expression MIN (expr) The lowest value in the expression

Syntax SELECT avg(price * 2) from titles returns the average of all prices * 2returns the average of all prices * 2 SELECT sum (price) from titles return the sum of the pricesreturn the sum of the prices