Duplicate entry Exception while generating UUID in Liquibase changeset - mysql

Question

I'm using a Liquibase changeset to update null values of the customId column. The sql is a modified version of this answer.
The problem is that it seems to use the same UUID for all rows. My changeset looks like this:
<changeSet id="v3.0.3" author="msp" runAlways="false">
<preConditions onFail="MARK_RAN">
<not>
<sqlCheck expectedResult="0">select count(*) from FOOBAR where customId is null</sqlCheck>
</not>
</preConditions>
<sql>update FOOBAR set customId = concat('cu:', (select uuid())) where customId is null</sql>
</changeSet>
Note that if I'm running this slightly modified version of the query (adding a limit of 2) in the MySQL console, then it works:
update FOOBAR set customId = concat('cu:', (select uuid())) where customId is null limit 2
But if I try to run the very same query (including the limit) with liquibase, I get the following Exception:
Caused by: liquibase.exception.MigrationFailedException: Migration failed for change set changelog/db.changelog-v3.0.3.xml::v3.0.3::msp:
Reason: liquibase.exception.DatabaseException: Error executing SQL update FOOBAR set customId = concat('cu:', (select uuid())) where customId is null limit 2: Duplicate entry 'cu:cde325da-f71f-11e5-95f8-d15a50829a7d' for key 'customId'
at liquibase.changelog.ChangeSet.execute(ChangeSet.java:554)
at liquibase.changelog.visitor.UpdateVisitor.visit(UpdateVisitor.java:43)
at liquibase.changelog.ChangeLogIterator.run(ChangeLogIterator.java:70)
at liquibase.Liquibase.update(Liquibase.java:195)
at liquibase.Liquibase.update(Liquibase.java:174)
at liquibase.integration.spring.SpringLiquibase.performUpdate(SpringLiquibase.java:330)
at liquibase.integration.spring.SpringLiquibase.afterPropertiesSet(SpringLiquibase.java:287)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1625)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1562)
... 77 more
Caused by: liquibase.exception.DatabaseException: Error executing SQL update FOOBAR set customId = concat('cu:', (select uuid())) where customId is null limit 2: Duplicate entry 'cu:cde325da-f71f-11e5-95f8-d15a50829a7d' for key 'customId'
at liquibase.executor.jvm.JdbcExecutor.execute(JdbcExecutor.java:62)
at liquibase.executor.jvm.JdbcExecutor.execute(JdbcExecutor.java:122)
at liquibase.database.AbstractJdbcDatabase.execute(AbstractJdbcDatabase.java:1206)
at liquibase.database.AbstractJdbcDatabase.executeStatements(AbstractJdbcDatabase.java:1189)
at liquibase.changelog.ChangeSet.execute(ChangeSet.java:518)
... 85 more
Caused by: com.mysql.jdbc.exceptions.jdbc4.MySQLIntegrityConstraintViolationException: Duplicate entry 'cu:cde325da-f71f-11e5-95f8-d15a50829a7d' for key 'customId'
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
at com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
at com.mysql.jdbc.Util.getInstance(Util.java:386)
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1039)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4096)
at com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:4028)
at com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:2490)
at com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2651)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2677)
at com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2627)
at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:841)
at com.mysql.jdbc.StatementImpl.execute(StatementImpl.java:681)
at com.mchange.v2.c3p0.impl.NewProxyStatement.execute(NewProxyStatement.java:1006)
at liquibase.executor.jvm.JdbcExecutor$ExecuteStatementCallback.doInStatement(JdbcExecutor.java:310)
at liquibase.executor.jvm.JdbcExecutor.execute(JdbcExecutor.java:55)
... 89 more
Note that there's of course a UNIQUE constraint on customId - but shouldn't select uuid() (also tried uuid() without select) generate a unique value, even when using Liquibase?

Answer 1

The problem can be solved with a small workaround. I split the update into two queries:
<changeSet id="v3.0.3" author="msp" runAlways="false">
<preConditions onFail="MARK_RAN">
<not>
<sqlCheck expectedResult="0">select count(*) from FOOBAR where customId is null</sqlCheck>
</not>
</preConditions>
<sql>update FOOBAR set customId = (select uuid())) where customId is null</sql>
<sql>update FOOBAR set customId = concat('cu:', customId) where length(customId) = 36
</changeSet>
This of course only works for my case where I can be sure that all rows of the first query can be identified by length(customId) = 36.