If these are corrupted, there goes your index. Tuesday, July 29, AM. Any ideas? Tuesday, July 29, PM. Something here doesn't make sense, so let's back up. You're adding records to a table from a script. What kind of script? How are you accessing the data? It it's not doing so, something is very wrong. Maybe it's something wrong with the provider? I wonder if the collating sequence is the problem. The default collating sequence for VFP is machine.
If the tables were created with machine collation, maybe trying to use General would cause trouble. Wednesday, July 30, PM. Thank you for your respond! That is why I belive that there is something with the permissions. Thursday, July 31, PM. I opened the DBF file with a program called DBF Manager and it says that the file is dBase I believe that the program might be wrong, but I'm not sure Also, when I opened Index Manager in the same program, it says that there are no index files connected to that database, even though there is one.
Any ideas or thoughts? Btw, any suggestion on where I can find programs that can open index files? Code Snippet. Sna wrote: Code Snippet. Alex Feldstein wrote: Conn. You have to use separate instructions. One to open, one to index. Both in one as you stated it is wrong VFP syntax. If you pasted that list of indexes so that it's accurate, the problem is the use IF as a function. However, if you retyped, I suspect you may have introduced a typo. Friday, August 1, PM. I really hoped it was a typo Saturday, August 2, AM.
I don't know if this is important or not, but it's good to know. Is there a different CDX version? Is this something I should worry about? Saturday, August 2, PM. This is starting to sound like the original author did something very non-standard. Monday, August 4, PM. Tuesday, August 5, PM. Or anything else that is helpful? If the CDX has the same name as the table, it will be automatically opened with the table. Can you please tell me how to open the CDX file or maybe paste a link?
Wednesday, August 6, PM. Rather than storing a zero or a blank, which could be interpreted to have meaning, you could store a null value in the field until the information becomes available. To control entering null values per field In the Table Designer, select or clear the Null column for the field. When the Null column is selected, you can enter null values in the field. To permit null values in all table fields In the Table Designer, select the Null column for each table field.
For example, the following code creates a table that allows nulls in every table field:. The presence of null values affects the behavior of tables and indexes. After you create a table in an open database, you can add a description of each table field to make your tables easier to understand and update. Visual FoxPro displays a field s comment text in the Project Manager when you select the field in the list of fields for the table.
To add a comment to a field in a database table In the Table Designer, enter the text for your comment in the Field Comment box. If you want Visual FoxPro to fill the contents of a field automatically as you add a new record, you can create a default value for the field. The default value is applied whether you enter data through a form, in a Browse window, a view, or programmatically, and remains in the field until you enter a new value.
You create default values either through the Table Designer or through the language. You can specify default values for any data type except General. To assign a default value to a database table field In the Table Designer, enter the value in the Default value box in the Field validation area.
For example, you might want your application to limit the amount of merchandise a new customer can order until you ve had time to complete a credit check and determine the amount of credit you re willing to extend to that customer.
The following example creates a maxordamt field with a default value of If your customer table already included the maxordamt column, you could add a default value for the column with this command:.
You can use default values to speed data entry for your application s users, enabling them to skip a field unless they want to enter a different value. For example, if your business primarily deals with domestic customers, you may want the country field in the customer table in a database to be filled with the name of your country automatically. If you re entering a customer record for an international customer, you can then overwrite the name of your country with their country name.
Tip If one of your application s business rules requires that a field contain an entry, providing a default value helps to ensure that a particular field-level or record-level rule will not be violated. If you remove or delete a table from a database, all default values bound to that table are deleted from the database.
Stored procedures referenced by the removed or deleted default value remain even after the default value has been removed. This preserves backward compatibility with any existing FoxPro code you might have.
You can use. You can specify default values that are either scalar values such as a number or expressions that evaluate to a scalar quantity. You can also specify any valid Xbase expression that returns a value consistent with the data type for the field.
Visual FoxPro evaluates expressions for data type when the table structure is closed. If the data type doesn t match the associated field type, Visual FoxPro generates an error. However, when either of these commands is issued, defaults will not overwrite existing values in fields. If appended or inserted fields contain values, the existing value is retained as the record is appended or inserted and the default value is not applied.
Default values are particularly useful to automatically populate fields that do not allow null values. When you add a new record, default values are applied first, then each field is checked in definition order for missing information. By specifying an input mask, you define the punctuation, spacing, and other format attributes of values as they are entered into the field.
The values are then stored in a uniform manner which can reduce data entry errors and make processing more efficient. For example, adding a mask to a numeric field storing telephone numbers helps the user to quickly fill out the field because the punctuation and spaces are already provided by the mask. To provide an input mask In the Table Designer, enter the mask in the Input mask box in the Display area. Additional properties for fields allow you to control how a field and its values appear on forms, Browse windows, and reports.
You can specify a display format, a default field caption, and a default class and class library. A format provides an output mask that determines the manner in which the value of a field is displayed in a form, Browse window, or report. For example:. You can create a caption for each field in a database table. Visual FoxPro displays a field s caption text as the column header in a Browse window and as the default header name in a form grid.
To add a caption to a field in a database table In the Table Designer, enter the text for your caption in the Caption box in the Display area. To save time later when you're creating forms, you can set a default class for a field. Once set, each time you add the field to a form, the control on the form uses the class you specify as the default.
For example, character fields automatically appear as text box controls when you add them to a form. If you want to automatically create a combo box control instead when you use the field in a form, you can set that class as the default for this field. You can also use class libraries that you've created.
If you find you're often changing the library and class for your fields, you can map the fields data types to a library and class in the Options dialog box. For more information about mapping your field data types to classes, see Chapter 3, Configuring Visual FoxPro, in the Installation Guide.
For more information about creating classes, see Chapter 3, Object-Oriented Programming, in this book. You can enforce business rules for data entry by creating field-level and record-level rules, called validation rules, to control the data entered into database table fields and records.
Field- and record-level rules compare the values entered against the rule expressions that you define. If the entered value does not meet the requirements of the rule, the value is rejected. Validation rules exist only in database tables. Field- and record-level rules enable you to control the types of information entered into a table, whether the data is accessed through a Browse window, a form, or programmatically through the language. They allow you to consistently enforce the rule for a field with less coding than if you wrote the rule expression as code in a VALID clause on a form, or in a portion of program code.
In addition, the rules you establish in a database are enforced for all users of the table, regardless of the requirements of the application. You can also create candidate or primary indexes that prevent duplicate entries in a field, and triggers to enforce referential integrity or perform other actions when the data in your database is changed.
You choose database constraints based on the level at which you want to enforce a business or referential integrity rule, as well as the action that causes the constraint to be activated. The following table lists the data validation constraints in the order in which they are enforced by the Visual FoxPro engine, the level at which they are applied, and when the engine activates the validation.
Constraints are activated in the order in which they appear in the table. The first violation of any validation test stops the command. Candidate and primary indexes are explained later in this chapter in the section Controlling Duplicate Values. When you want to control the type of information a user can enter into a field, and you can validate the data in a field independently of any other entry in the record, you use a field-level validation rule.
For example, you might use a field-level validation rule to ensure that the user doesn t enter a negative number in a field that should contain only positive values. You can also use a field-level rule to compare the values entered in a field against the values in another table. You should not create field- or record-level rules that are application-specific.
Use field- and record-level validation rules to enforce data integrity and business rules that always apply to the data in your database, regardless of who may access the data.
To create a field-level rule In the Table Designer, enter the rule expression in the Rule box in the Field validation area. For example, the following code adds a field-level validation rule to the orditems table requiring that numbers entered into the quantity field be 1 or greater:. When the user attempts to enter a value less than 1, Visual FoxPro displays an error and the value is rejected. You can customize the message displayed when the rule is violated by adding validation text to the field.
The text you enter is displayed instead of the default error message. To add a custom error message to a field-level rule In the Table Designer, enter the error message you want in the Message box in the Field validation area.
For example, the following code adds both a field-level validation rule for the orditems table requiring that numbers entered into the quantity column must be 1 or greater, as well as a custom error message:. When the user attempts to enter a value less than 1, Visual FoxPro displays an error with the custom error message you defined, and rejects the failed value.
Field-level rules are checked when the field s value changes. Unlike triggers, field-level rules fire even if data is buffered. When you work with data in a Browse window, form, or other window, Visual FoxPro checks field-level rules as you move away from the field. If a field value has not been changed, the rule is not checked. This means that you are free to tab through fields without the system validating any of the data. You use record-level validation rules to control the type of information a user can enter into a record.
Record-level validation rules typically compare the values of two or more fields in the same record to make sure they follow the business rules established for the database. For example, you can use a record-level validation rule to ensure that one field s value is always greater than that of another in the same record.
To create a record-level validation rule and custom error message In the Table tab of the Table Designer, enter the rule and error message you want in the Rule and Message boxes.
For example, you might want to ensure employees are 18 years or older when hired. If the user enters an employee record with an invalid date, Visual FoxPro displays an error with the custom error message you defined, and does not update the record.
You should ensure that any rules specified for fields do not conflict semantically with the rules you define for the table. Visual FoxPro makes no attempt to compare the field-level and record-level expressions for consistency. Record-level rules, like field-level rules, activate when the record value changes. No matter how you work with data, whether in a Browse window, form, or other user interface window, or through commands that alter data, Visual FoxPro checks record-level rules as you move the record pointer off the record.
If no values within the record have changed, the record-level rule is not checked when you move the record pointer. You are free to move through records without the system validating any of the data. If you modify a record, but don't move the record pointer, and then close the Browse window, the rule is still checked. You're warned of any errors that occur, and the Browse window is closed. Caution Do not include any commands or functions in your validation rules that attempt to move the record pointer in the current work area that is, in the work area whose rules are being checked.
Unlike triggers, record-level rules fire even if data is buffered. When a record-level rule fires during a running application, you need to include error handling code. Typically, this will mean not allowing the application to leave the form or change the active environment, to be more generic until the user either corrects the reported error or cancels the update.
If you remove or delete a table from a database, all field-level and record-level rules bound to that table are deleted from the database.
This is because the rules are stored in the. However, stored procedures referenced by the removed or deleted rule are not deleted. They are not automatically removed, because they may be used by rules in other tables that remain in the database. A trigger is an expression that is bound to a table and is invoked when any of the table s records are modified by one of the specified data-modification commands.
Triggers can be used to perform any side-effect operations that a database application requires when data is modified. For example, you can use triggers to:.
Triggers are created and stored as properties on a specific table. If you remove a table from a database, the triggers associated with that table are deleted. Triggers fire after all other checks, such as validation rules, primary key enforcement, and null value enforcement, are performed.
And unlike field- and record-level validation rules, triggers don t fire on buffered data. A table can have a maximum of three triggers at any one time. A trigger must return a true. To create a trigger In the Table tab of the Table Designer, enter the trigger expression or the name of a stored procedure containing the trigger expression in the Insert trigger , Update trigger , or Delete trigger box.
You can create an Update trigger on the products table to accomplish this. To create the trigger, you can specify updProductsTrigger as your Update trigger for the products table.
You can then add this code to your stored procedure:. To delete a trigger In the Table tab of the Table Designer, select the trigger expression in the Insert trigger , Update trigger , or Delete trigger box and delete it. If you remove or delete a table from a database, all triggers bound to that table are deleted from the database.
However, stored procedures referenced by the removed or deleted trigger are not deleted. To modify a trigger In the Table tab of the Table Designer, enter the new trigger expression in the Insert trigger , Update trigger , or Delete trigger box. After you ve built a table you can always modify the table structure and properties. You may want to add, change or delete field names, widths, data types, change default values or rules, or add comments or captions. Make sure you have exclusive access to the table before modifying its structure.
To modify the structure of a table with the Table Designer In the Project Manager, select the table name and then choose Modify. For example, you can modify the structure of the database table employee with the following commands:. Some clauses apply only to tables associated with a database. A few specific examples are included in this section. To add a field to a table In the Table Designer, choose Insert.
For example, the following command adds a field called fax to the customer table and allows the field to have null values:. To delete a field from a table In the Table Designer, select the field and choose Delete. For example, the following command drops the field called fax from the customer table:. Removing a field from a table also removes the field s default value setting, rule definitions, and caption. If index key or trigger expressions reference the field, the expressions become invalid when the field is removed.
The invalid index key or trigger expression will not generate an error until run time. To rename a table field In the Table Designer, enter a new field name in the Name box for the existing field. For example, to rename the column company in the customer table, you could issue the following command:.
In the previous example, the new field name takes advantage of the ability to create long field names in database tables. To change an existing rule In the Table Designer, select the Table tab and enter the new rule expression or rule text in the Rule and Message boxes in the Record validation section.
To change an existing default value In the Table Designer, enter the new value in the Default value box of the Fields tab. Once you ve designed and created the structure for a table, you can store data in the table by adding new records. Later, you ll change and delete existing records.
Each of these tasks can be accomplished either through the interface or by using commands. This section focuses primarily on working with records programmatically.
For more information about working with records through the interface, see Chapter 2, Creating Tables and Indexes, in the User s Guide. When you first create a Visual FoxPro table, it is open but empty. If you try to store data to a table without first creating a record in the table, nothing happens. The first step in adding records to a new table is to add rows to store the new data.
For example, to insert a new record into the TasTrade database customer table, you could issue the following command:. Another way to store data in records is to copy them from other tables or files.
For example, you can append records from another table or file. Records can accept data directly, as in the previous example, where the INSERT command specified the text to be inserted into specific fields in the customer table, as well as from constants, variables, arrays, objects, and other data sources. For more information about other ways to import data, see Chapter 9, Importing and Exporting Data, in the User s Guide.
If you want to add a new record while viewing a table in browse mode, you can choose Append Record from the Table menu. For more information on record and table buffering, see Chapter 17, Programming for Shared Access. For example, the following code displays the customer table in a Browse window in edit mode:. If you want to use a form to edit a record, create a text box in your form and set its DataSource property to the name of the table you want to edit.
For more information about forms, see Chapter 9, Creating Forms. You can store graphics in a Visual FoxPro table by creating a General field and importing or pasting OLE objects, such as bitmaps or charts, into the field. You can enter a null value in a field through the language with the NULL token, or through the interface with a key combination if the field accepts null values.
For example, the following code replaces the existing value in the field automobile with a null value:. Note: The software discussed here is no longer in common use at IU, and UITS may no longer be able to verify this text's accuracy; additionally, the UITS Support Center may no longer have the materials needed to adequately support this software. There are several differences between index files in the various xBase dialects and flavors.
FoxPro deals with all types from other dialects, so if you use FoxPro, you need not be too concerned with those differences, which are explained in this document. NDX file extension. How many data types are there in visual foxpro? Visual FoxPro creates an index key for each record in the table based on the index expression and stores the index keys in an index file. The index file contains and maintains pointers to records in the table.
Indexing and sorting are two methods that can be used to create an order in a data table. Indexing would create an index file that contains only the logical order of rows along with their physical position in the table whereas with sorting , a copy of the sorted table has to be stored.
Indexing is broadly referred to as an indicator or measure of something. In the financial markets, indexing can be used as a statistical measure for tracking economic data, a methodology for grouping a specific market segment, or an investment management strategy for passive investments.
There are approximately 5, U. The three most widely followed indexes in the U. The Wilshire includes all the stocks from the U. Indexing is very much important to protect file and documents of large size business organization. Indexing helps to locate the position of the specific document in files at a short period of time.
The cross-reference means the preservation of files at the appropriate location by more than one name or number. Types of indexing Bibliographic and database indexing. Genealogical indexing. Geographical indexing. Book indexing.
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