Index Segments (Magic xpa 4.x)
The order of appearance of the segments in the table reflects their hierarchical strength (major/intermediate/minor) in order of decreasing significance. The order of appearance of segments influences the sorting sequence for this index. The Index Segment repository can store segments that are up to 32,767 characters long.
Note: The maximum number of segments for each index is different for each DBMS.
The Index Segment repository includes the following columns:
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This read-only column contains an automatically generated sequential number used by Magic xpa as an index segment identifier.
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Column
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The number of the table column to be used as segment. You can enter the number you want or you can zoom to the Column list displayed on the right to select the column you want.
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Name
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The name of the column chosen as a segment. The cursor skips this column.
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Size
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The cursor parks in this column only if the column attribute is Alpha. You can then shorten the size of the segment column to attempt to improve performance of searches. If you do shorten the segment, it is advisable to define the Index as Non-Unique, to prevent loss of rows. However, specifying Non-Unique may impose performance penalties of its own, so it is not always certain that shortening a segment by a few bytes will improve performance.
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You should not modify this property when using SQL databases.
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Order
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The segment order may utilize an Alternate Collating Sequence if specified in the Environment dialog box. This occurs when the segment is an Alpha column and its Translate property is Standard. Magic xpa only supports one alternate collating sequence at a time. It is also important to ensure that all tables being accessed when an alternate collating sequence is active were created using the same sequence. If this is not the case, Magic xpa can be confused as to the true collating sequence of these tables, and Range/Locate queries may give incorrect results.
You select Ascending or Descending from the Order box to define the Index Segment’s sort direction.
If the link's Direction is different than the index segment's Order, performance will be slower, depending on the database.
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