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SQL Data Retrieval Basics

kirestin-pollard avatar
kirestin-pollard
13 diapositives · 227 Views · Oct 25, 2014

Learn the fundamentals of SQL SELECT queries to extract data from a database. Understand syntax for specifying fields, tables, criteria, sorting, aliases, calculations, and handling NULL values.

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SQL Data Retrieval Basics
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  1. SQL SELECT Getting Data from the Database

  2. Basic Format SELECT <fieldname>,<fieldname> FROM <tablename> WHERE <fieldname> (=, >, < , <> LIKE, IN) <some criteria> ORDER BY <fieldname>; SELECT LastName, FirstName, Phone, City FROM Customer WHERE City=‘Seattle’ ORDER BY LastName;

  3. Key Words • SELECT –every query that returns data starts with SELECT • FROM –determines what table(s) • WHERE –sets up the Criteria • ORDER BY –sorts by the field(s) listed Note: SELECT * FROM Customer, the * means select all columns

  4. AS, Aliasing • The names of the columns may not always be the names you wish to use in a query result. You can use the AS keyword to alias it for the result SELECT LastName AS “Last Name”, FirstName AS “First Name” FROM Customer;

  5. Calculated Fields SELECT 5 * 3 / 2; SELECT lastname + ‘, ‘ firstname AS “Customer Name”, Phone FROM Customer; SELECT OrderID, (ItemPrice * Quantity) AS “SubTotal” FROM OrderDetail WHERE OrderID=1223;

  6. ORDER BY • ORDER BY sorts by the selected field in an Ascending order by default. • You can add the DESC keyword to change the sort order to Descending • If you have multiple fields the leftmost is the primary sort, the next leftmost is the secondary sort etc. SELECT LastName, FirstName, City, phone FROM Customer ORDER BY City, LastName DESC; Note: the DESC only applies to the LastName field

  7. WHERE CRITERIA • You can use all the basic comparative operators

  8. Criteria • Number values are used without quotes • Character (text) values are quoted with single ‘’ quotes • Dates are quoted with single quotes except in Access where they put between pound # signs

  9. Between • You can use the BETWEEN keyword to look for values “between” to limiting values. • The Between includes the ends SELECT OrderID, OrderDate FROM Order WHERE OrderDate BETWEEN #1/1/2007# AND #1/31/2007#;

  10. AND OR NOT • SELECT * • FROM Customer • WHERE State = ‘WA’ • AND City = “Seattle” • OR City = “Tacoma” • AND NOT City = “Bellevue”

  11. LIKE • With the keyword LIKE in conjunction with wildcards will let you search for patterns in text fields • The wild cards are • % any string of characters • _ any one character

  12. LIKE Examples SELECT * FROM Customer WHERE LastName LIKE ‘Ch%’; SELECT * FROM Course WHERE CourseName LIKE ‘MIC12_’

  13. Nulls • You can search for Nulls with the key words IS NULL • SELECT SectionNumber, StudentID, QuarterGrade • FROM Section • WHERE SectionID=‘2830’ • AND QuarterGrade IS NULL