day 16: access chapter 2 tazin afrin [email protected] [email protected] october 10,...
TRANSCRIPT
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SINGLE TABLE QUERIES
• Which customer currently has a balance over $5000?– Create a query
• A query enables you to ask questions about the data stored in a database.
• Need reference of table– For previous question refer Account table
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QUERY DESIGN VIEW
• Query Design view enables you to create queries; the Design view is divided into two parts – – the top portion displays the tables– the bottom portion (known as the query
design grid) displays the fields and the criteria.
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SINGLE TABLE QUERY
• Create in two ways – – Simple query wizard:
• provides dialog boxes to guide you through the query design process.
• helpful for users who are not experienced.
– Query design tool:• For more advanced users• Provides the most flexibility
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QUERY DATASHEET
• Display the results of the query.• Query’s datasheet looks and acts like a table’s
datasheet• Usually a subset of the records from the table. • Only shows the records that match the criteria.• Allows you to enter a new record, modify an existing
record, or delete a record. • Any changes made in Datasheet view are reflected in
the underlying table.• Caution: Changes Made to Query Results Overwrite
Table Data
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SINGLE – TABLE SELECT QUERY
• A select query displays only the records that match the criteria entered in Design view.
• Create -> Queries -> Query Design• Show Table Dialog Box appears• Select table• Add query
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USE QUERY DESIGN VIEW
• Consists of two parts:– The top portion contains tables with their
respective field names. – The bottom portion (known as the query
design grid) contains columns and rows. • Field row• Table row• Sort row• Show row• Criteria row
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WILDCARD
• A wildcard is a special character that can represent one or more characters in the criterion of a query.
• * mark– Represents one or more characters– If name start with Sm search by Sm*– S*nd will return Sand, Stand, or StoryLand.
• ? mark– Stand for a single character– H?ll will return Hull, Hill, or Hall etc.
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COMPARISON OPERATORS
• A comparison operator can be used in the criteria of a query.
• Such as – – equal (=)– not equal (<>),– greater than (>)– less than (<)– greater than or equal to (>=)– and less than or equal to (<=)
• Query for salary >5000
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NULL
• Null is the term Access uses to describe a blank field.
• Example:– Is Null
• For an Employee field in the Customers table when the customer has not been assigned a sales representative.
– Is Not Null • For the ShipDate field; a value inserted indicates
the order was shipped to the customer.
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ESTABLISH LOGICAL CRITERIA
• The AND logical operator returns only records that meet all criteria.
• The OR logical operator returns records meeting any of the specified criteria.
• The NOT logical operator returns all records except the specified criteria.
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MULTI-TABLE QUERY
• A multi-table query contains two or more tables.
• Enables you to take advantage of the relationships that have been set in your database.
• Related tables should already be established when you create a multi-table query.– Related tables are tables that are joined in a
relationship using a common field.
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MORE OPERATIONS
• Add additional tables• Get answers using query• Modify multi-table query• Add and delete fields
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COMMON MISTAKE
• Use tables in query who are not joined.– Results in more rows than usual– For example, If we create a query on Customer table and
Branch table but forget to join them.– Suppose Customers table contains 11 records, and the
Branch table contains 5 records. – Since Access does not know how to interpret the unrelated
tables, the results will show 55 records –every possible combination of customer and branch (11*5).
• When add new table, create relationships.• Temporary join line in query will not create an actual
join line between tables.
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NEXT CLASS
• Access Chapter 3– Order of operations.– Create a calculated field.– Create expressions.– Use built-in functions.– Perform date arithmetic.