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https://issues.apache.org/jira/browse/DERBY-3175?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#action_12541435
]
Bryan Pendleton commented on DERBY-3175:
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Here are 3 possible ways to ensure that the autoincrementValue is preserved
during the drop column:
1) Add autoincrementValue to ColumnDescriptor. Change
SYSCOLUMNS.buildDescriptor to
retrieve the autoincrementValue from the SYSCOLUMNS row. Change
SYSCOLUMNS.makeRow
to set the autoincrementValue in SYSCOLUMNS from the ColumnDescriptor's value.
Change
any other places that create a ColumnDescriptor to initialize the
autoincrementValue to match
autoincrementStart.
2) Change SYSCOLUMNS.makeRow to take a new 3rd argument: autoincrementValue.
Change
AlterTableCOnstantAction's drop column logic so that it fetches the old value
of the
autoincrementValue from the SYSCOLUMNS row before it deletes it, then passes
that old value
to the makeRow call when adding back the column descriptor. I don't really like
this solution,
but I thought of it so I'm recording it here.
3) Change AlterTableConstantAction's drop column logic so that it doesn't
drop-and-re-add
all the subsequent column descriptors in order to change their positions, but
instead issues
an UPDATE operation on those column descriptors to decrement their column
number field.
Technique #1 seems pretty straightforward, it's just a bunch of code grunging.
It does make the
ColumnDescriptor object instance slightly larger in memory.
Technique #3 seems appealing, because if all we want to change about a
particular
SYSCOLUMNS row is the column number, why should we have to delete and re-add the
SYSCOLUMNS row in order to make that change? It doesn't appear that the column
number
field in SYSCOLUMNS is indexed, so I don't think there should be any index
complexity.
If I can find some example code for one of the other system catalogs which
issues an UPDATE
rather than a DROP and an INSERT, I'll try to implement technique #3 modelled
on that.
> NullPointerException on INSERT after ALTER TABLE ... DROP COLUMN
> ----------------------------------------------------------------
>
> Key: DERBY-3175
> URL: https://issues.apache.org/jira/browse/DERBY-3175
> Project: Derby
> Issue Type: Bug
> Components: SQL
> Affects Versions: 10.3.1.4, 10.4.0.0
> Reporter: Knut Anders Hatlen
> Assignee: Bryan Pendleton
> Attachments: bug.sql, d3175_codeChangeOnly.diff,
> fixWith3177Case.diff, fixWithTest.diff
>
>
> ij version 10.3
> ij> connect 'jdbc:derby:bugdb;create=true';
> ij> create table t (
> x varchar(12),
> y varchar(12),
> id int primary key generated by default as identity
> );
> 0 rows inserted/updated/deleted
> ij> alter table t drop column y;
> 0 rows inserted/updated/deleted
> ij> insert into t(x) values 'a';
> ERROR XJ001: Java exception: ': java.lang.NullPointerException'.
> java.sql.SQLException: Java exception: ': java.lang.NullPointerException'.
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory40.getSQLException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.Util.newEmbedSQLException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.Util.javaException(Unknown Source)
> at
> org.apache.derby.impl.jdbc.TransactionResourceImpl.wrapInSQLException(Unknown
> Source)
> at
> org.apache.derby.impl.jdbc.TransactionResourceImpl.handleException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.EmbedConnection.handleException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.ConnectionChild.handleException(Unknown
> Source)
> at org.apache.derby.impl.jdbc.EmbedStatement.execute(Unknown Source)
> at org.apache.derby.impl.jdbc.EmbedStatement.execute(Unknown Source)
> at org.apache.derby.impl.tools.ij.ij.executeImmediate(Unknown Source)
> at org.apache.derby.impl.tools.ij.utilMain.doCatch(Unknown Source)
> at org.apache.derby.impl.tools.ij.utilMain.runScriptGuts(Unknown
> Source)
> at org.apache.derby.impl.tools.ij.utilMain.go(Unknown Source)
> at org.apache.derby.impl.tools.ij.Main.go(Unknown Source)
> at org.apache.derby.impl.tools.ij.Main.mainCore(Unknown Source)
> at org.apache.derby.impl.tools.ij.Main14.main(Unknown Source)
> at org.apache.derby.tools.ij.main(Unknown Source)
> at org.apache.derby.iapi.tools.run.main(Unknown Source)
> Caused by: java.sql.SQLException: Java exception: ':
> java.lang.NullPointerException'.
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory.getSQLException(Unknown Source)
> at
> org.apache.derby.impl.jdbc.SQLExceptionFactory40.wrapArgsForTransportAcrossDRDA(Unknown
> Source)
> ... 18 more
> Caused by: java.lang.NullPointerException
> at
> org.apache.derby.impl.sql.compile.ResultColumn.columnTypeAndLengthMatch(Unknown
> Source)
> at
> org.apache.derby.impl.sql.compile.ResultColumnList.columnTypesAndLengthsMatch(Unknown
> Source)
> at org.apache.derby.impl.sql.compile.InsertNode.bindStatement(Unknown
> Source)
> at org.apache.derby.impl.sql.GenericStatement.prepMinion(Unknown
> Source)
> at org.apache.derby.impl.sql.GenericStatement.prepare(Unknown Source)
> at
> org.apache.derby.impl.sql.conn.GenericLanguageConnectionContext.prepareInternalStatement(Unknown
> Source)
> ... 11 more
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