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INSERT statement limitations

  • Artykuł

Inserted data is truncated on the right without warning if it's too long to fit into the column.

Attempting to insert a value that is out of the range of a column's data type causes a NULL to be inserted into the column.

When a dBASE, Microsoft Excel, Paradox, or Text driver is used, inserting a zero-length string into a column actually inserts a NULL instead.

When the Microsoft Excel driver is used, if an empty string is inserted into a column, the empty string is converted to a NULL; a searched SELECT statement that is executed with an empty string in the WHERE clause doesn't succeed on that column.

A table isn't updatable by the Paradox driver under two conditions:

  • When a unique index isn't defined on the table. This isn't true for an empty table, which can be updated with a single row even if a unique index isn't defined on the table. If a single row is inserted in an empty table that doesn't have a unique index, an application can't create a unique index or insert more data after the single row is inserted.

  • If the Borland Database Engine isn't implemented, only read and append statements are allowed on the Paradox table.

When the Text driver is used, NULL values are represented by a blank-padded string in fixed-length files, but are represented by no spaces in delimited files. For example, in the following row containing three fields, the second field is a NULL value:

"Smith:,, 123

When the Text driver is used, all column values can be padded with leading spaces. The length of any row must be less than or equal to 65,543 bytes.