Guofeng Cao CyberInfrastructure and Geospatial Information Laboratory Department of Geography National Center for Supercomputing Applications (NCSA) University of Illinois at Urbana-Champaign Geog 480: Principles of GIS

Introduction to SQL

3 SQL Overview Structured Query Language The standard for relational database management systems (RDBMS) SQL-92 and SQL-99 Standards – Purpose: o Specify syntax/semantics for data definition and manipulation o Define data structures o Enable portability o Specify minimal (level 1) and complete (level 2) standards o Allow for later growth/enhancement to standard

4 SQL Environment Catalog o A set of schemas that constitute the description of a database Schema o The structure that contains descriptions of objects created by a user (base tables, views, constraints) Data Definition Language (DDL) o Commands that define a database, including creating, altering, and dropping tables and establishing constraints Data Manipulation Language (DML) o Commands that maintain and query a database Data Control Language (DCL) o Commands that control a database, including administering privileges and committing data

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6 SQL Data types String types o CHAR(n) – fixed-length character data, n characters long Maximum length = 2000 bytes o VARCHAR(n) – variable length character data, maximum 4000 bytes Numeric types o NUMBER(p,q) – general purpose numeric data type o INTEGER(p) – signed integer, p digits wide o FLOAT(p) – floating point in scientific notation with p binary digits precision Binary Large Objects(BLOB) o Byte Array Geometry types o Box2d, box3d, point, linestring, polygon Date/time type o DATE – fixed-length date/time in dd-mm-yy form

Hands-on keyItemcount keyItemprice

Connecting to Geog480 server

Connecting to Database psql -U username -d database_name o username = geog480 o database_name = tutorial o Enter passwd when prompted (same as username) Postgres Commands o \l List all accessible databases o \dt List all the tables in current DB o \? Help o \q Quite

Table Creation SQL CREATE TABLE Syntax o CREATE TABLE table_name ( column_name1 data_type, column_name2 data_type, column_name3 data_type,.... ) Table Creation Example: o create table count (key int, item varchar(20),count int); o create table price (key int, item varchar(20),price float); Copy from a CSV file (postgres specific) o \COPY count FROM ‘/srv/cigi/code/test.csv' with CSV HEADER

Table Insertion SQL CREATE TABLE Syntax o INSERT INTO table_name VALUES (value1, value2, value3,...) Insertion Example: o insert into count values(1, ‘item0', 100); o insert into count values(2, ‘item1', 101); o insert into count values(3, ‘item2, 102); Copy from a CSV file (postgres specific) o \COPY count FROM ‘/srv/cigi/code/test.csv' with CSV HEADER

Select Table Syntax Used for queries on single or multiple tables Clauses of the SELECT statement: (Sequence!!) o SELECT List the columns (and expressions) that should be returned from the query o FROM Indicate the table(s) or view(s) from which data will be obtained o WHERE Indicate the conditions under which a row will be included in the result o GROUP BY Indicate categorization of results o HAVING Indicate the conditions under which a category (group) will be included o ORDER BY Sorts the result according to specified criteria

Select Table Examples List contents of table o select * from count; o select * from count where item =‘item1'; o Select * from count order by key asc; o select key, count from count limit 5; Counting o select count(*) from count; o select count(*) from count where item like '%1'; Max/Min/Avg o select max(count) from count; o select avg(count) from count where item like '%1%';

Update Tables SQL UPDATE Syntax o UPDATE table_name SET column1=value, column2=value2,... WHERE some_column=some_value Update table Examples: o update count set item =‘item1' where key =1; o update count set count =105 where key=1; Delete Rows o delete from count where key=1;

Join Tables SQL JOIN Syntax o SELECT column_name(s) FROM table_name1 JOIN table_name2 ON table_name1.column_name=table_name2.column_name Example: Join o select count.key, count.item, count.count, price.price from count join price on count.item = price.item;

Using and Defining Views Views provide users controlled access to tables Base Table–table containing the raw data Concepts of View o A “virtual table” created dynamically upon request by a user o No data actually stored; instead data from base table made available to user o Based on SQL SELECT statement on base tables or other views

Create View SQL Syntax o CREATE VIEW view_name AS SELECT column_name(s) FROM table_name WHERE condition Example: Create view: o Create view stock as select count.key, count.item, count.count, price.price from count join price on count.item = price.item;

View Operations Very similar to table operations Multiply two columns o Select count*price as value from stock Drop view o Drop view stock

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