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Behavior When Adding Columns to a Table

Document Type | Technical Information

Category | Administration

Document Number | TADTI063

 

Overview

This explains the internal procedures that are performed when adding a column to a table.
 
 
 

Method

Behavior When Adding Columns to a Table

1. Column Validity and Information Check
  • A semantic check is performed on the newly added column, and the column information is verified and processed.
 
2. Enter Column Information
  • _dd_col table is updated with the information of the corresponding column.
 
3. If the Existing Table Has LONG or LONG RAW Type Columns
  • The col_no value of the LONG column is modified.
  • A physical operation to push the LONG column to the back is also performed.
 
4. If the Newly Added Column is of LOB Type
  • _dd_lob is updated with lob-related information.
  • A LOB Segment is created.
 
5. When a Default Value is Specified
  • An update operation occurs to set the data for the newly added column in all rows.
 
6. When Constraints are Created Together
  • VALIDATE option triggers a validity check. Depending on the need, a SELECT operation may be performed.
  • If a Primary Key or Unique constraint is set, an index creation operation is also performed. The basic operation is similar to the CREATE INDEX operation.
Caution
Operations That May Take a Long Time When Adding Table Columns
  • Physical relocation of LONG columns
  • When a default value is specified
  • When the VALIDATE option is specified during constraint creation and an index must be created
 

 

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