Structured(Query(Language - people.tamu.edupeople.tamu.edu/~alawing/materials/ESSM464/SQL.pdf · Structured$Query$Language$(SQL)$ ... For$example,$the$following$expression$would$selectall$the$houses$thathave$more$than$

ESSM 464: Spa*al Project Management Ecosystem Science and Management | Texas A&M University (c) 2015, A. Michelle Lawing

Structured Query Language Dr. Michelle Lawing Ecosystem Science and Management Texas A&M University College Sta*on, TX 77843 [email protected]


Today In Class

•  Announcements

•  Quiz

•  Lecture (sql)

•  Break

•  Lab


Announcements

•  Website is updated

•  ASPRS for Thursday, April 09 at 5:30 in 214 Centeq

•  Jenny Oakley (Family emergency) – work on case study regarding EIH

•  Homework – read case studies (I will post online)


Job Announcement: GIS Analyst Loca*on: Tyler, TX Job Purpose -  E.L.S. Surveying & Mapping, Inc. is an all-‐inclusive surveying firm specializing in oil and gas.

Primary du*es for this posi*on include: crea*ng geodatabase deliverables using ArcGIS, CAD and Microsog Excel. This posi*on is intended to provide our clients with survey grade data in a polished deliverable format.

Du:es and Responsibili:es -  Create geodatabase deliverables using ESRI sogware -  Entering data efficiently and accurately -  Using CAD in conjunc*on with ESRI sogware -  Maintain survey grade precision in ArcMap environment Qualifica:ons -  Proficient with ESRI sogware (ArcMap, ArcCatalog, etc.) -  Microsog Office experience -  Knowledge of CAD preferred -  Programming skills are a plus. -  Ability to work well with others in a team oriented environment

To apply, please submit resume to [email protected]


ESSM Recep*on

•  April 17th 6pm •  hjp://essm.tamu.edu/


Footprints 5K

•  April 18th •  hjp://essm.tamu.edu/footprints/


Updates on Team Progress (your role+)

•  Overview of project

•  Overall project status

•  The objec*ves accomplished since the last week •  Upcoming ac*vi*es


Quiz


Structured Query Language (SQL)


SQL

•  standard computer language for accessing and managing databases

•  SQL expressions are used in many parts of ArcGIS •  define a subset of data on which to perform some opera*on

•  You use it in ArcMap to select features with the Select by Ajributes dialog box

•  You use it in ArcMap in the Query Builder dialog box to set a layer defini*on query


SQL

•  You use it in geoprocessing to define a subset of features •  You use it in geoprocessing to define records to perform

an opera*on on •  You also use SQL to select features programma*cally •  We will review the basic WHERE clause expressions •  For the SQL beginner •  Detailed reference here (hjp://webhelp.esri.com/

arcgisdesktop/9.2/index.cfm?TopicName=SQL_Reference)


A simple SQL expression

•  SELECT * FROM forms the first part of the SQL expression

•  This is usually automa*cally supplied for you •  The hard-‐coded SELECT * syntax means that you must select ALL the columns

•  DISTINCT, ORDER BY, GROUP BY, and so on, cannot be used readily in a SQL query except when using subqueries


A simple SQL expression

•  Depending on the dialog box in which you are building your query, the name of the layer or table may be supplied for you or you may need to choose it from a drop-‐down list

•  The next part of the expression is the WHERE clause, which is the part you must build.

•  A basic SQL WHERE clause would look like STATE_NAME = ‘Texas’


SQL Syntax

•  The syntax you use to build a SQL expression differs depending on the data source.

•  SQL is a standard, but not all database sogware implements the same dialect of SQL.

•  To query personal geodatabases, you use the same syntax used in Microsog Access.

•  To query an ArcSDE geodatabase, you use the SQL syntax of the underlying database management system (DBMS)—either Oracle, SQL Server, DB2, or Informix.


SQL Syntax

•  The dialog boxes you create SQL WHERE clauses with help you –  use the correct syntax for the data you're querying –  list the field names and values with the appropriate delimiters

–  select the relevant keywords and operators for you


Searching Strings •  Strings must always be enclosed within single quotes. •  For example

"STATE_NAME" = ‘California’

•  Strings in expressions are case sensi*ve •  Use an SQL func*on to convert all values to the same

case •  UPPER or LOWER func*on •  For example, the following will select a last name stored

as either Jones or JONES: UPPER("LAST_NAME") = 'JONES'


Searching Strings

•  UCASE and LCASE perform the same opera*on for a personal geodatabase

•  Use the LIKE operator (instead of the = operator) to build a par*al string search.

•  For example, this expression would select Mississippi and Missouri among USA state names: "STATE_NAME" LIKE 'Miss%'


Search Strings

•  % means that anything is acceptable in its place –  one character –  a hundred characters –  no character

•  Alterna*vely, if you want to search with a wildcard that represents one character, use _

•  For example, this expression would find Catherine Smith and Katherine Smith: "OWNER_NAME" LIKE '_atherine smith'


Search Strings

•  The wildcards work for any file-‐based data or mul*user geodatabase data.

•  The wildcards you use to query personal geodatabases are * for any number of characters and ? for one character.

•  Wildcard characters appear as bujons on the Select by Ajributes and Query Builder dialog boxes.

•  If you use a wildcard character in a string with the = operator, the character is treated as part of the string, not as a wildcard.


Search Strings

•  Select based on sor*ng order –  greater than (>) –  less than (<) –  greater than or equal (>=) –  less than or equal (<=) –  BETWEEN –  not equal (<>)

•  For example, this expression will select all the ci*es in a coverage with names star*ng with the lejers M to Z: "CITY_NAME" >= 'M'


The Null Keyword

•  Select null values for a specified field. •  The NULL keyword is always preceded by IS or IS NOT.

•  For example, to find ci*es whose 1996 popula*on has not been entered, you can use "POPULATION96" IS NULL

•  Alterna*vely, to find ci*es whose 1996 popula*on has been entered, you can use "POPULATION96" IS NOT NULL


Searching Numbers •  Query numbers by

–  the equal (=) –  not equal (<>) –  greater than (>) –  less than (<) –  greater than or equal (>=) –  less than or equal (<=) –  BETWEEN

•  For example "POPULATION96" >= 5000

•  Numeric values are always listed using the point as the decimal delimiter regardless of your regional se}ngs (PROBLEM IN INTERNATIONAL SETTING).

•  The comma cannot be used as a decimal or thousands delimiter in an expression.


Calcula*ons •  Calcula*ons can be included in expressions using the

arithme*c operators: + -‐ * / •  Calcula*ons can be between fields and numbers. •  For example:

"AREA" >= "PERIMETER" * 100

•  Calcula*ons can also be performed between fields. •  For example, to find the countries with a popula*on density

of less than or equal to 25 people per square mile, you could use this expression: "POP1990" / "AREA" <= 25


Operator precedence •  Expressions evaluate according to standard operator

precedence rules. •  For example, the part of an expression enclosed in

parentheses is evaluated before the part that isn't enclosed.

"HOUSEHOLDS" > "MALES" * "POP90_SQMI" + "AREA“ evaluates differently from

"HOUSEHOLDS" > "MALES" * ("POP90_SQMI" + "AREA")


Combining expressions •  Complex expressions can be built by combining expressions with the AND and OR operators.

For example, the following expression would select all the houses that have more than 1,500 square feet and a garage for three or more cars:

•  "AREA" > 1500 AND "GARAGE" > 3 When you use the OR operator, at least one side of the expression of the two separated by the OR operator must be true for the record to be selected. For example: "RAINFALL" < 20 OR "SLOPE" > 35 Use the NOT operator at the beginning of an expression to find features or records that don't match the specified expression. For example: NOT "STATE_NAME" = 'Colorado' NOT expressions can be combined with AND and OR. For example, this expression would select all the New England states except Maine: "SUB_REGION" = 'New England' AND NOT "STATE_NAME" = 'Maine'


Subqueries •  A subquery is a query nested within another query and

are supported by geodatabase data sources only. They can be used to apply predicate or aggregate func*ons or to compare data with values stored in another table. For example, this query would select only the countries that are not also listed in the table indep_countries:

•  "COUNTRY_NAME" NOT IN (SELECT "COUNTRY_NAME" FROM indep_countries) For more informa*on, see SQL Reference.


Querying Dates

•  Some changes have been introduced in ArcGIS 9 for building expressions that query date fields. The appropriate syntax for the underlying data source is automa*cally shown in the unique values list or generated by the Query Builder. Most of the *me, you will only need to click the field, the operator, and the value to generate the proper syntax.


Documents

Structured(Query(Language - people.tamu.edupeople.tamu.edu/~alawing/materials/ESSM464/SQL.pdf · Structured$Query$Language$(SQL)$ ... For$example,$the$following$expression$would$selectall$the$houses$thathave$more$than$