public Class DB2Dialect

Overrides org.hibernate.dialect.Dialect.convertToFirstRowValue.

DB2 does have a one-based offset, however this was actually already handled in the limit string building (the '?+1' bit). To not mess up inheritors, I'll leave that part alone and not touch the offset here.

Parameters

zeroBasedFirstResult:int

The user-supplied, zero-based offset

Returns:int

zeroBasedFirstResult

Overrides org.hibernate.dialect.Dialect.doesReadCommittedCauseWritersToBlockReaders.

Doc from org.hibernate.dialect.Dialect.doesReadCommittedCauseWritersToBlockReaders.

For the underlying database, is READ_COMMITTED isolation implemented by forcing readers to wait for write locks to be released?

Returns:boolean

True if writers block readers to achieve READ_COMMITTED; false otherwise.

Overrides org.hibernate.dialect.Dialect.dropConstraints.

Doc from org.hibernate.dialect.Dialect.dropConstraints.

Do we need to drop constraints before dropping tables in this dialect?

Returns:boolean

True if constraints must be dropped prior to dropping the table; false otherwise.

Overrides org.hibernate.dialect.Dialect.generateTemporaryTableName.

Doc from org.hibernate.dialect.Dialect.generateTemporaryTableName.

Generate a temporary table name given the base table.

Parameters

baseTableName:String

The table name from which to base the temp table name.

Returns:String

The generated temp table name.

Overrides org.hibernate.dialect.Dialect.getAddColumnString.

Doc from org.hibernate.dialect.Dialect.getAddColumnString.

The syntax used to add a column to a table (optional).

Returns:String

The "add column" fragment.

Overrides org.hibernate.dialect.Dialect.getCreateSequenceString.

Doc from org.hibernate.dialect.Dialect.getCreateSequenceString.

Typically dialects which support sequences can create a sequence with a single command. This is convenience form of getCreateSequenceStrings to help facilitate that.

Dialects which support sequences and can create a sequence in a single command need *only* override this method. Dialects which support sequences but require multiple commands to create a sequence should instead override getCreateSequenceStrings.

Parameters

sequenceName:String

The name of the sequence

Returns:String

The sequence creation command

Overrides org.hibernate.dialect.Dialect.getCreateTemporaryTablePostfix.

Doc from org.hibernate.dialect.Dialect.getCreateTemporaryTablePostfix.

Get any fragments needing to be postfixed to the command for temporary table creation.

Returns:String

Any required postfix.

Overrides org.hibernate.dialect.Dialect.getCreateTemporaryTableString.

Doc from org.hibernate.dialect.Dialect.getCreateTemporaryTableString.

Command used to create a temporary table.

Returns:String

The command used to create a temporary table.

Overrides org.hibernate.dialect.Dialect.getCrossJoinSeparator.

Doc from org.hibernate.dialect.Dialect.getCrossJoinSeparator.

Get the separator to use for defining cross joins when translating HQL queries.

Typically this will be either [ cross join ] or [, ]

Note that the spaces are important!

Overrides org.hibernate.dialect.Dialect.getCurrentTimestampSelectString.

Doc from org.hibernate.dialect.Dialect.getCurrentTimestampSelectString.

Retrieve the command used to retrieve the current timestamp from the database.

Returns:String

The command.

Overrides org.hibernate.dialect.Dialect.getDropSequenceString.

Doc from org.hibernate.dialect.Dialect.getDropSequenceString.

Typically dialects which support sequences can drop a sequence with a single command. This is convenience form of getDropSequenceStrings to help facilitate that.

Dialects which support sequences and can drop a sequence in a single command need *only* override this method. Dialects which support sequences but require multiple commands to drop a sequence should instead override getDropSequenceStrings.

Parameters

sequenceName:String

The name of the sequence

Returns:String

The sequence drop commands

Overrides org.hibernate.dialect.Dialect.getForUpdateString.

Doc from org.hibernate.dialect.Dialect.getForUpdateString.

Get the string to append to SELECT statements to acquire locks for this dialect.

Returns:String

The appropriate FOR UPDATE clause string.

Overrides org.hibernate.dialect.Dialect.getIdentityColumnString.

Doc from org.hibernate.dialect.Dialect.getIdentityColumnString.

The syntax used during DDL to define a column as being an IDENTITY.

Returns:String

The appropriate DDL fragment.

Overrides org.hibernate.dialect.Dialect.getIdentityInsertString.

Doc from org.hibernate.dialect.Dialect.getIdentityInsertString.

The keyword used to insert a generated value into an identity column (or null). Need if the dialect does not support inserts that specify no column values.

Returns:String

The appropriate keyword.

Overrides org.hibernate.dialect.Dialect.getIdentitySelectString.

Doc from org.hibernate.dialect.Dialect.getIdentitySelectString.

Get the select command to use to retrieve the last generated IDENTITY value.

Returns:String

The appropriate select command

Overrides org.hibernate.dialect.Dialect.getLimitString.

Doc from org.hibernate.dialect.Dialect.getLimitString.

Apply s limit clause to the query.

Typically dialects utilize variable limit clauses when they support limits. Thus, when building the select command we do not actually need to know the limit or the offest since we will just be using placeholders.

Here we do still pass along whether or not an offset was specified so that dialects not supporting offsets can generate proper exceptions. In general, dialects will override one or the other of this method and getLimitString(String, int, int).

Parameters

sql:String

The query to which to apply the limit.

hasOffset:boolean

Is the query requesting an offset?

Returns:String

the modified SQL

Overrides org.hibernate.dialect.Dialect.getLowercaseFunction.

Doc from org.hibernate.dialect.Dialect.getLowercaseFunction.

The name of the SQL function that transforms a string to lowercase

Returns:String

The dialect-specific lowercase function.

Overrides org.hibernate.dialect.Dialect.getQuerySequencesString.

Doc from org.hibernate.dialect.Dialect.getQuerySequencesString.

Get the select command used retrieve the names of all sequences.

Returns:String

The select command; or null if sequences are not supported.

Overrides org.hibernate.dialect.Dialect.getResultSet.

Doc from org.hibernate.dialect.Dialect.getResultSet.

Given a callable statement previously processed by registerResultSetOutParameter, extract the java.sql.ResultSet from the OUT parameter.

Parameters

ps:CallableStatement

The callable statement.

Returns:ResultSet

The extracted result set.

Exceptions

SQLException:

Indicates problems extracting the result set.

Overrides org.hibernate.dialect.Dialect.getSelectClauseNullString.

Doc from org.hibernate.dialect.Dialect.getSelectClauseNullString.

Given a java.sql.Types type code, determine an appropriate null value to use in a select clause.

One thing to consider here is that certain databases might require proper casting for the nulls here since the select here will be part of a UNION/UNION ALL.

Parameters

sqlType:int

The java.sql.Types type code.

Returns:String

The appropriate select clause value fragment.

Overrides org.hibernate.dialect.Dialect.getSequenceNextValString.

Doc from org.hibernate.dialect.Dialect.getSequenceNextValString.

Generate the appropriate select statement to to retrieve the next value of a sequence.

This should be a "stand alone" select statement.

Parameters

sequenceName:String

the name of the sequence

Returns:String

String The "nextval" select string.

Overrides org.hibernate.dialect.Dialect.isCurrentTimestampSelectStringCallable.

Doc from org.hibernate.dialect.Dialect.isCurrentTimestampSelectStringCallable.

Should the value returned by getCurrentTimestampSelectString be treated as callable. Typically this indicates that JDBC escape syntax is being used...

Returns:boolean

True if the getCurrentTimestampSelectString return is callable; false otherwise.

Overrides org.hibernate.dialect.Dialect.registerResultSetOutParameter.

Doc from org.hibernate.dialect.Dialect.registerResultSetOutParameter.

Registers an OUT parameter which will be returning a java.sql.ResultSet. How this is accomplished varies greatly from DB to DB, hence its inclusion (along with getResultSet) here.

Parameters

statement:CallableStatement

The callable statement.

col:int

The bind position at which to register the OUT param.

Returns:int

The number of (contiguous) bind positions used.

Exceptions

SQLException:

Indicates problems registering the OUT param.

Overrides org.hibernate.dialect.Dialect.requiresCastingOfParametersInSelectClause.

DB2 in fact does require that parameters appearing in the select clause be wrapped in cast() calls to tell the DB parser the type of the select value.

Returns:boolean

True.

Overrides org.hibernate.dialect.Dialect.supportsCommentOn.

Overrides org.hibernate.dialect.Dialect.supportsCurrentTimestampSelection.

Doc from org.hibernate.dialect.Dialect.supportsCurrentTimestampSelection.

Does this dialect support a way to retrieve the database's current timestamp value?

Returns:boolean

True if the current timestamp can be retrieved; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsEmptyInList.

Doc from org.hibernate.dialect.Dialect.supportsEmptyInList.

Does this dialect support empty IN lists?

For example, is [where XYZ in ()] a supported construct?

Returns:boolean

True if empty in lists are supported; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsIdentityColumns.

Doc from org.hibernate.dialect.Dialect.supportsIdentityColumns.

Does this dialect support identity column key generation?

Returns:boolean

True if IDENTITY columns are supported; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsLimit.

Doc from org.hibernate.dialect.Dialect.supportsLimit.

Does this dialect support some form of limiting query results via a SQL clause?

Returns:boolean

True if this dialect supports some form of LIMIT.

Overrides org.hibernate.dialect.Dialect.supportsLobValueChangePropogation.

Doc from org.hibernate.dialect.Dialect.supportsLobValueChangePropogation.

Does the dialect support propagating changes to LOB values back to the database? Talking about mutating the internal value of the locator as opposed to supplying a new locator instance...

For BLOBs, the internal value might be changed by: java.sql.Blob#setBinaryStream, java.sql.Blob#setBytes(long, byte[]), java.sql.Blob#setBytes(long, byte[], int, int), or java.sql.Blob#truncate(long).

For CLOBs, the internal value might be changed by: java.sql.Clob#setAsciiStream(long), java.sql.Clob#setCharacterStream(long), java.sql.Clob#setString(long, String), java.sql.Clob#setString(long, String, int, int), or java.sql.Clob#truncate(long).

NOTE : I do not know the correct answer currently for databases which (1) are not part of the cruise control process or (2) do not supportsExpectedLobUsagePattern.

Returns:boolean

True if the changes are propagated back to the database; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsNotNullUnique.

Overrides org.hibernate.dialect.Dialect.supportsOuterJoinForUpdate.

Doc from org.hibernate.dialect.Dialect.supportsOuterJoinForUpdate.

Does this dialect support FOR UPDATE in conjunction with outer joined rows?

Returns:boolean

True if outer joined rows can be locked via FOR UPDATE.

Overrides org.hibernate.dialect.Dialect.supportsParametersInInsertSelect.

Doc from org.hibernate.dialect.Dialect.supportsParametersInInsertSelect.

Does this dialect support parameters within the SELECT clause of INSERT ... SELECT ... statements?

DB2 is know to support parameters in the SELECT clause, but only in casted form (see requiresCastingOfParametersInSelectClause()).

Returns:boolean

True.

Overrides org.hibernate.dialect.Dialect.supportsPooledSequences.

Doc from org.hibernate.dialect.Dialect.supportsPooledSequences.

Does this dialect support "pooled" sequences. Not aware of a better name for this. Essentially can we specify the initial and increment values?

Returns:boolean

True if such "pooled" sequences are supported; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsResultSetPositionQueryMethodsOnForwardOnlyCursor.

Doc from org.hibernate.dialect.Dialect.supportsResultSetPositionQueryMethodsOnForwardOnlyCursor.

Does this dialect support asking the result set its positioning information on forward only cursors. Specifically, in the case of scrolling fetches, Hibernate needs to use java.sql.ResultSet#isAfterLast and java.sql.ResultSet#isBeforeFirst. Certain drivers do not allow access to these methods for forward only cursors.

NOTE : this is highly driver dependent!

Returns:boolean

True if methods like java.sql.ResultSet#isAfterLast and java.sql.ResultSet#isBeforeFirst are supported for forward only cursors; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsSequences.

Doc from org.hibernate.dialect.Dialect.supportsSequences.

Does this dialect support sequences?

Returns:boolean

True if sequences supported; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsTemporaryTables.

Doc from org.hibernate.dialect.Dialect.supportsTemporaryTables.

Does this dialect support temporary tables?

Returns:boolean

True if temp tables are supported; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsTupleDistinctCounts.

Doc from org.hibernate.dialect.Dialect.supportsTupleDistinctCounts.

Does this dialect support `count(distinct a,b)`?

Returns:boolean

True if the database supports counting disintct tuples; false otherwise.

Overrides org.hibernate.dialect.Dialect.supportsUnionAll.

Doc from org.hibernate.dialect.Dialect.supportsUnionAll.

Does this dialect support UNION ALL, which is generally a faster variant of UNION?

Returns:boolean

True if UNION ALL is supported; false otherwise.

Overrides org.hibernate.dialect.Dialect.useMaxForLimit.

Doc from org.hibernate.dialect.Dialect.useMaxForLimit.

Does the LIMIT clause take a "maximum" row number instead of a total number of returned rows?

This is easiest understood via an example. Consider you have a table with 20 rows, but you only want to retrieve rows number 11 through 20. Generally, a limit with offset would say that the offset = 11 and the limit = 10 (we only want 10 rows at a time); this is specifying the total number of returned rows. Some dialects require that we instead specify offset = 11 and limit = 20, where 20 is the "last" row we want relative to offset (i.e. total number of rows = 20 - 11 = 9)

So essentially, is limit relative from offset? Or is limit absolute?

Returns:boolean

True if limit is relative from offset; false otherwise.