NonStop SQL/MP Reference Manual

NonStop SQL/MP Reference Manual—142115
L-6
Limits
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Base tables per view
A view definition can include a maximum of 16 base tables in a FROM clause.
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Block size
The largest allowed block size is 4096 bytes.
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Clustering key length
The sum of the column lengths for the columns of the key cannot exceed 247 bytes.
SQL appends an 8-byte SYSKEY column to the columns specified for the clustering
key, making the maximum actual physical key length 255.
•
Column heading
The SQLCI report writer imposes a maximum of 50 lines on a column heading. Any
new-line character following the 49th one is text and does not create a new line.
Column headings are defined with the HEADING clause of the CREATE or ALTER
statements for a table or view.
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Columns per index
The maximum number of columns allowed for an index is 254 minus the number of
columns in the primary key of the underlying table.
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Columns per table
The maximum number of columns allowed per table depends on the column
definitions with these restrictions:
°
The sum of the lengths of the columns in a row must not exceed the maximum
row length (see the Row length item later in this subsection). In determining the
column length for a varying-length character column, use the maximum
declared length plus two bytes. For example, suppose that you declare a
VARCHAR column of the maximum row length. The limit for the number of
columns in this situation is one.
For each column that can contain null values, add two bytes to the column
length.
°
The description of the table must fit in the file label. The number of columns
that fits depends on the data types of the columns and on the presence of default
values. File label restrictions can reduce the maximum number of columns
allowed to as few as 128.
•
Columns per view
The maximum number of columns allowed for a view is between 200 and 400,
depending on the size of the column definitions. The size of the column definitions
depends on the data types of the columns and the complexity and number of
operators that define the selection of rows. The descriptions of the columns of the
view must fit in a file label.
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