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Advanced Select Statements

Advanced Select Statements. Select List Variations. SELECT * Column Naming Arithmetic Expressions Constants Strings. Column Naming. Using column aliases we can control how the column names are displayed in our output. SELECT au_fname First_Name FROM authors

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Advanced Select Statements

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  1. Advanced Select Statements

  2. Select List Variations • SELECT * • Column Naming • Arithmetic Expressions • Constants • Strings

  3. 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 -------------- Joe Dan Sue

  4. Expressions Arithmetic expressions can be used in the select list of a SELECT statement. • Column (+-*/) Column • eg. Unit_cost * items_sold • Constant (+-*/) Column • eg. Unit_cost * 1.1 • Constant • Functions • eg. Avg(sales)

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

  6. Precedence Hierarchy of Arithmetic Operators ParenthesesMultiplication, DivisionAddition, Subtraction (2+2*3)/4 = 2

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

  8. Precedence Hierarchy of Logical Operators ParenthesesMultiplication, DivisionAddition, SubtractionNOTANDOR

  9. 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)

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

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

  12. 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

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

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