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Data Type
QR Code ISO/IEC18004 Recognizer In None
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Denso QR Bar Code Maker In None
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Description
Decoding QR-Code In None
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QR Code Printer In C#.NET
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CHAR(len) CHARACTER(len) VARCHAR(len) CHAR VARYING(len) CHARACTER VARYING(len) NCHAR(len) NATIONAL CHAR(len) NATIONAL CHARACTER(len) NCHAR VARYING(len) NATIONAL CHAR VARYING(len) NATIONAL CHARACTER VARYING(len) INTEGER INT
Create QR Code In .NET Framework
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Printing QR Code 2d Barcode In Visual Studio .NET
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Fixed-length character strings
QR Creation In VB.NET
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Barcode Generation In None
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Variable-length character strings*
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Fixed-length national character strings*
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Variable-length national character strings*
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Bar Code Generation In None
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Integer numbers
Paint Code 128B In VS .NET
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Code 128C Recognizer In Java
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Code 39 Extended Generation In None
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SMALLINT BIT(len) BIT VARYING(len) NUMERIC(precision,scale) DECIMAL(precision,scale) DEC(precision,scale) FLOAT(precision) REAL DOUBLE PRECISION DATE TIME(precision) TIMESTAMP(precision) INTERVAL
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ANSI/AIM Code 128 Drawer In None
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Small integer numbers Fixed-length bit string* Variable-length bit string* Decimal numbers
Floating point numbers Low-precision floating point numbers High-precision floating point numbers Calendar date* Clock time* Date and time* Time interval*
*new data type in SQL2
The differences between the data types offered in various SQL implementations is one of the practical barriers to the portability of SQL-based applications. These differences have come about as a result of innovation as relational databases have evolved to include a broader range of capabilities. The typical pattern has been: A DBMS vendor adds a new data type that provides useful new capability for a certain group of users. Other DBMS vendors add the same or similar data types, adding their own innovations to differentiate their products from the others. Over several years, the popularity of the data type grows, and it becomes a part of the "mainstream" set of data types supported by most SQL implementations. The standards bodies become involved to try to standardize the new data type and eliminate arbitrary differences between the vendor implementations. The more wellentrenched the data type has become, the more difficult the set of compromises faced by the standards group. Usually this results in an addition to the standard that does not exactly match any of the current implementations. DBMS vendors slowly add support for the new standardized data type as an option to their systems, but because they have a large installed base that is using the older (now "proprietary") version of the data type, they must maintain support for this form of the data type as well. Over a very long period of time (typically several major releases of the DBMS product),
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users migrate to the new, standardized form of the data type, and the DBMS vendor can begin the process of obsoleting the proprietary version. Date/time data provides an excellent example of this phenomenon and the data type variations it creates. DB2 has long offered support for three different date/time data types: DATE, which stores a date like June 30, 1991, TIME, which stores a time of day like 12:30 P.M., and TIMESTAMP, which is a specific instant in history, with a precision down to the nanosecond. Specific dates and times can be specified as string constants, and date arithmetic is supported. Here is an example of a valid query using DB2 dates, assuming that the HIREDATE column contains DATE data: SELECT NAME, HIRE_DATE FROM SALESREPS WHERE HIRE_DATE >= '05/30/1989' + 15 DAYS SQL Server provides a single date/time data type, called DATETIME, which closely resembles the DB2 TIMESTAMP data type. If HIRE_DATE contained DATETIME data, SQL Server could accept this version of the query (without the date arithmetic): SELECT NAME, HIRE_DATE FROM SALESREPS WHERE HIRE_DATE >= '06/14/1989' Since no specific time on June 14, 1989, is specified in the query, SQL Server defaults to midnight on that date. The SQL Server query thus really means: SELECT NAME, HIRE_DATE FROM SALESREPS WHERE HIRE_DATE >= '06/14/1989 12:00AM' If a salesperson's hire date was stored in the database as midday on June 14, 1989, the salesperson would not be included in the SQL Server query results but would have been included in the DB2 results (because only the date would be stored). SQL Server also supports date arithmetic through a set of built-in functions. Thus the DB2-style query can also be specified in this way: SELECT NAME, HIRE_DATE FROM SALESREPS WHERE HIRE_DATE >= DATEADD(DAY, 15, '05/30/1989') which, of course, is considerably different from the DB2 syntax. Oracle also supports date/time data, with a single data type called DATE. Like SQL Server's DATETIME type, an Oracle DATE is, in fact, a timestamp. Also like SQL Server, the time part of an Oracle DATE value defaults to midnight if no time is explicitly specified. The default Oracle date format is different from the DB2 and SQL Server formats, so the Oracle version of the query becomes: SELECT NAME, HIRE_DATE
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FROM SALESREPS WHERE HIRE_DATE >= '14-JUN-89' Oracle also supports limited date arithmetic, so the DB2-style query can also be specified but without the DAYS keyword: SELECT NAME, HIRE_DATE FROM SALESREPS WHERE HIRE_DATE >= '30-MAY-89' + 15 Finally, the ANSI/ISO SQL2 standard added support for date/time data with a set of data types that are based on, but not identical to, the DB2 types. In addition to the DATE, TIME, and TIMESTAMP data types, the standard specifies an INTERVAL data type, which can be used to store a time interval (for example, a timespan measured in days, or a duration measured in hours, minutes, and seconds). The standard also provides a very elaborate and complex method for dealing with date/time arithmetic, specifying the precision of intervals, adjusting for time zone differences, and so on. As these examples illustrate, the subtle differences in data types among various SQL products lead to some significant differences in SQL statement syntax. They can even cause the same SQL query to produce slightly different results on different database management systems. The widely praised portability of SQL is thus true but only at a general level. An application can be moved from one SQL database to another, and it can be highly portable if it uses only the most mainstream, basic SQL capabilities. However, the subtle variations in SQL implementations mean that data types and SQL statements must almost always be adjusted somewhat if it is to be moved across DBMS brands. The more complex the application, the more likely it is to become dependent on DBMS-specific features and nuances, and the less portable it will become.
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