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Rules for Entering Search Values

  • Artykuł

This topic discusses the conventions you must use when entering the following types of literal values for a search condition:

  • Text values

  • Numeric values

  • Dates

  • Logical values

Note

The information in this topic is derived from the rules for standard SQL-92. However, each database can implement SQL in its own way. Therefore, the guidelines provided here might not apply in every case. If you have questions about how to enter search values for a particular database, refer to the documentation for the database that you are using.

Searching on Text Values

The following guidelines apply when you enter text values in search conditions:

  • Quotation marks   Enclose text values in single quotation marks, as in this example for a last name:

    'Smith'

    If you are entering a search condition in the Criteria Pane, you can simply type the text value and the Query and View Designer will automatically put single quotation marks around it.

    Note

    In some databases, terms in single quotation marks are interpreted as literal values, whereas terms in double quotation marks are interpreted as database objects such as column or table references. Therefore, even though the Query and View Designer can accept terms in double quotation marks, it might interpret them differently than you expect.

  • Embedding apostrophes   If the data you are searching for contains a single quotation mark (an apostrophe), you can enter two single quotation marks to indicate that you mean the single quotation mark as a literal value and not a delimiter. For example, the following condition searches for the value "Swann's Way:"

    ='Swann''s Way'

  • Length limits   Do not exceed the maximum length of the SQL statement for your database when entering long strings.

  • Case sensitivity   Follow the case sensitivity rules for the database you are using. The database you are using determines whether text searches are case sensitive. For example, some databases interpret the operator "=" to mean an exact case-sensitive match, but others will allow matches on any combination of uppercase and lowercase characters.

    If you are unsure about whether the database uses a case-sensitive search, you can use the UPPER or LOWER functions in the search condition to convert the case of the search data, as illustrated in the following example:

    WHERE UPPER(lname) = 'SMITH'

    For details about the functions to convert to uppercase and lowercase letters, see Functions for Expressions.

Searching on Numeric Values

The following guidelines apply when you enter numeric values in search conditions:

  • Quotation marks   Do not enclose numbers in quotation marks.

  • Non-numeric characters   Do not include non-numeric characters except the decimal separator (as defined in the Regional Settings dialog box of Windows Control Panel) and negative sign (-). Do not include digit grouping symbols (such as a comma between thousands) or currency symbols.

  • Decimal marks   If you are entering whole numbers, you can include a decimal mark, whether the value you are searching for is an integer or a real number.

  • Scientific notation   You can enter very large or very small numbers using scientific notation, as in this example:

    > 1.23456e-9

Searching on Dates

The format you use to enter dates depends on the database you are using and in what pane of the Query and View Designer you are entering the date.

Note

If you don't know which format your data source uses, type a date into the filter column of the Criteria pane in any format familiar to you. The designer will convert most of such entries into the appropriate format.

The Query and View Designer can work with the following date formats:

  • Locale-specific   The format specified for dates in the Windows Regional Settings Properties dialog box.

  • Database-specific   Any format understood by the database.

  • ANSI standard date   A format that uses braces, the marker 'd' to designate the date, and a date string, as in the following example:

    { d '1990-12-31' }

  • ANSI standard datetime   Similar to ANSI-standard date, but uses 'ts' instead of 'd' and adds hours, minutes, and seconds to the date (using a 24-hour clock), as in this example for December 31, 1990:

    { ts '1990-12-31 00:00:00' }

    In general, the ANSI standard date format is used with databases that represent dates using a true date data type. In contrast, the datetime format is used with databases that support a datetime data type.

The following table summarizes the date format that you can use in different panes of the Query and View Designer.

Pane

Date format

Criteria

Locale-specific Database-specific ANSI standard

Dates entered in the Criteria Pane are converted to a database-compatible format in the SQL pane.

SQL

Database-specific ANSI standard

Results

Locale-specific

Searching on Logical Values

The format of logical data varies from database to database. Very frequently, a value of False is stored as zero (0). A value of True is most frequently stored as 1 and occasionally as -1. The following guidelines apply when you enter logical values in search conditions:

  • To search for a value of False, use a zero, as in the following example:

    SELECT * FROM authors
WHERE contract = 0

  • If you are not sure what format to use when searching for a True value, try using 1, as in the following example:

    SELECT * FROM authors
WHERE contract = 1

  • Alternatively, you can broaden the scope of the search by searching for any non-zero value, as in the following example:

    SELECT * FROM authors
WHERE contract <> 0

See Also

Other Resources

Specifying Search Criteria