Chapter 10 Queries and Updating Part C. SQL Copyright 2005 Radian Publishing Co.

2/28 Contents Chapter 10 Queries and Updating 10.1 Simple Query 10.1 A. Select * 10.1 B. Selecting Individual Columns10.1 B. Selecting Individual Columns 10.1 C. Queries with Distinction 10.1 D. Ordering the Result 10.1 E. Efficiency Issue with Order 10.1 F. Specifying Alias for Column10.1 F. Specifying Alias for Column 10.1 G. Simple Expressions in Query10.1 G. Simple Expressions in Query 10.2 The WHERE Clause 10.2 A. Using Logical Operators 10.2 B. The IN Operator 10.2 C. The BETWEEN … AND Operator10.2 C. The BETWEEN … AND Operator 10.2 D. The LIKE Operator 10.3 Exporting the Query Results 10.3 A. Outputting as a New Table 10.3 B. Outputting as a a Text File 10.4 Updating and Deleting Records 10.4 A. The SQL UPDATE 10.4 B. The SQL DELETE

Copyright 2005 Radian Publishing Co.3/28 Chapter 10 Queries and Updating In this chapter, you will learn how to query the data contained in tables using the SQL SELECT command. You will also learn how to update and delete records using SQL UPDATE and DELETE commands.

Copyright 2005 Radian Publishing Co.4/ Simple Query A query is a simple request to retrieve information from a database using criteria.

Copyright 2005 Radian Publishing Co.5/ A. Select * (1/3) In SELECT *, the asterisk is a wildcard character that tells DBMS to return all the fields.

Copyright 2005 Radian Publishing Co.6/ A. Select * (2/3)

Copyright 2005 Radian Publishing Co.7/ A. Select * (3/3) A cursor is the result of a query. It is a read-only table available for browsing, reporting or input to application programs. It is temporary as it will be removed when the application is closed.

Copyright 2005 Radian Publishing Co.8/ B. Selecting Individual Columns The SQL command allows you to display any columns you want. SELECT FieldNames FROM TableName;

Copyright 2005 Radian Publishing Co.9/ C. Queries with Distinction The keyword DISTINCT is used to remove duplicate records in the query result. SELECT DISTINCT FieldNames FROM TableName;

Copyright 2005 Radian Publishing Co.10/ D. Ordering the Result (1/2) The basic syntax for ordering the result is SELECT [DISTINCT] FieldNames FROM TableName ORDER BY FieldName1, FieldName2 ¡K [ASC|DESC]

Copyright 2005 Radian Publishing Co.11/ D. Ordering the Result (2/2)

Copyright 2005 Radian Publishing Co.12/ E. Efficiency Issue with Order The efficiency of ordering can be improved by creating indexes. If a certain ordering is frequently needed, an index should be created for this ordering.

Copyright 2005 Radian Publishing Co.13/ F. Specifying Alias for Column (1/2) A column alias can provide more descriptive names for columns. For MySQL and Visual FoxPro, alias can be used in references in the ORDER BY and GROUP BY clauses, but this is not allowed in MS Access.

Copyright 2005 Radian Publishing Co.14/ F. Specifying Alias for Column (2/2)

Copyright 2005 Radian Publishing Co.15/ G. Simple Expressions in Query A query may consist of expressions instead of field names in the SELECT clause.

Copyright 2005 Radian Publishing Co.16/ The WHERE Clause The syntax of a SELECT statement with a WHERE clause is SELECT [DISTINCT] SelectItems FROM TableName WHERE Conditions ORDER BY OrderItem1 [, OrderItem2 ] ; Alias is not allowed in the WHERE clause for all DBMS. An exact match is required for both MySQL and MS Access, but not for Visual FoxPro. (Note: All the DBMS mentioned in the textbook are not case-sensitive. )

Copyright 2005 Radian Publishing Co.17/ A. Using Logical Operators Logical operators, AND, OR and NOT, are used in the WHERE clause.

Copyright 2005 Radian Publishing Co.18/ B. The IN Operator The IN operator returns true if the specified data matches any one of the elements in the given set.

Copyright 2005 Radian Publishing Co.19/ C. The BETWEEN … AND Operator The BETWEEN … AND operator returns true if the specified data falls between a starting value and an ending value inclusively.

Copyright 2005 Radian Publishing Co.20/ D. The LIKE Operator (1/2) The LIKE operator compares the skeletons of two strings. The wildcard (_) means any single character in the position. The wildcard (%) means any string in forming the skeleton.

Copyright 2005 Radian Publishing Co.21/ D. The LIKE Operator (2/2)

Copyright 2005 Radian Publishing Co.22/ Exporting the Query Results Since the result of a query will be lost when the application is closed, sometimes, you might want to store the results. Fig.10.2 Variations between DBMS in exporting query results

Copyright 2005 Radian Publishing Co.23/ A. Outputting as a New Table In MS Access, the syntax to output the query as a table is: SELECT [DISTINCT] SelectItems INTO OutTable FROM TableName... In MySQL, the syntax to output the query as a table is: CREATE TABLE OutTable SELECT SelectItems FROM TableName... In Visual FoxPro, the syntax to output the query as a table is: SELECT [DISTINCT] SelectItems INTO TABLE OutTable FROM TableName...

Copyright 2005 Radian Publishing Co.24/ B. Outputting as a a Text File In MySQL, the syntax to output the query result to a text file is: SELECT SelectItems INTO OUTFILE 'FileName' FROM TableName... In Visual FoxPro, the syntax to output the query result to a text file is: SELECT SelectItems TO FILE 'FileName' FROM TableName...

Copyright 2005 Radian Publishing Co.25/ A. The SQL UPDATE (1/2) The basic syntax for updating a set of records is UPDATE TableName SET FieldName1 = Expression1 [, FieldName2 = Expression2 ] WHERE Conditions;

Copyright 2005 Radian Publishing Co.26/ A. The SQL UPDATE (2/2)

Copyright 2005 Radian Publishing Co.27/ B. The SQL DELETE (1/2) The basic syntax for deleting a set of records is DELETE FROM TableName WHERE Conditions; If the WHERE clause is missed, all records will be deleted.

Copyright 2005 Radian Publishing Co.28/ B. The SQL DELETE (2/2) Delete those records with quantity less than 5 Delete all records