Change column from not null to nullable oracle

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2 Managing Database Objects

  http://docs.oracle.com/cd/B25329_01/doc/appdev.102/b25108/xedev_design.htm
For concatenated indexes, define the columns used in the index carefully so that the column with the fewest duplicate values is named first, the column with the next fewest duplicate values is second, and so on. For each row, Oracle Database XE stores each value in the column as a variable-length field unless a value exceeds the column's maximum length, in which case Oracle returns an error

Unique constraint and NULL values - Oracle Database

  http://bytes.com/topic/oracle/answers/65985-unique-constraint-null-values
Rather than going through the extra work of having unique composite indices do a special case check for any of the columns being null, they just left it that way. I believe you can create an after-insert statement-level trigger (not for each row) that CAN read the after-insert state of the subject table without mutating

PowerBuilder Tips

  http://www.artfulsoftware.com/pbtech.htm
SystemKey When the insertion point is not in a line edit and the user presses ALT or ALT + another key Timer When a specified number of seconds elapses after the Timer function has been called

  http://www.blogcoward.com/archive/2005/05/09/234.aspx
For some reason this post came up top in Google when I was trying to find out why my t-sql syntax was not quite right for adding multiple columns to an already existing table using a single alter statement.BTW - Tilt's response to Darrick is priceless. The problem statement is this: Can you do ALTER TABLE X ALTER COLUMN Y, Z, Qwithout it being 3 separate operations.The answer is no.Only a maniac would go in and start hacking the sys tables

Oracle Column Default Value Tips

  http://dba-oracle.com/t_oracle_column_default_value.htm
Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. At table creation time, adding a column default creates no overhead at all: create table t1 (id number default (0)); A column default is rarely changed at alter table time, but there are issues with NULL values and default values

Make a Oracle table column nullable

  http://www.dba-oracle.com/t_alter_table_column_null_value.htm
Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise