HSQLDialect

Does the LIMIT clause come at the start of the SELECT statement, rather than at the end?

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

For the underlying database, is REPEATABLE_READ isolation implemented by forcing writers to wait for read locks to be released?

Do we need to drop the temporary table after use? todo - clarify usage by Hibernate Version 1.8 GLOBAL TEMPORARY table definitions persist beyond the end of the session (data is cleared). If there are not too many such tables, perhaps we can avoid dropping them and reuse the table next time?

With HSQLDB 2.0, the table name is qualified with MODULE to assist the drop statement (in-case there is a global name beginning with HT_)

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

No fragment is needed if data is not needed beyond commit, otherwise should add "on commit preserve rows"

Command used to create a temporary table.

The name of the database-specific SQL function for retrieving the current timestamp.

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

Command used to drop a temporary table.

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

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

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.

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

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).

For HSQLDB 2.0, this is a copy of the base class implementation. For HSQLDB 1.8, only READ_UNCOMMITTED is supported.

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

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.

Generate the select expression fragment that will retrieve the next value of a sequence as part of another (typically DML) statement.

This differs from getSequenceNextValString(String) in that this should return an expression usable within another statement.

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

This should be a "stand alone" select statement.

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

Different behavior for GLOBAL TEMPORARY (1.8) and LOCAL TEMPORARY (2.0)

Possible return values and their meanings:

• TRUE - Unequivocally, perform the temporary table DDL in isolation.
• FALSE - Unequivocally, do not perform the temporary table DDL in isolation.
• null - defer to the JDBC driver response in regards to dataDefinitionCausesTransactionCommit()

todo - needs usage clarification If the SELECT statement is always part of a UNION, then the type of parameter is resolved by v. 2.0, but not v. 1.8 (assuming the other SELECT in the UNION has a column reference in the same position and can be type-resolved). On the other hand if the SELECT statement is isolated, all versions of HSQLDB require casting for "select ? from .." to work.

Does this dialect support column-level check constraints?

HSQLDB 1.8.x requires CALL CURRENT_TIMESTAMP but this should not be treated as a callable statement. It is equivalent to "select current_timestamp from dual" in some databases. HSQLDB 2.0 also supports VALUES CURRENT_TIMESTAMP

Does this dialect support empty IN lists?

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

Does this dialect support identity column key generation?

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

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: setBinaryStream(long), setBytes(long, byte[]), setBytes(long, byte[], int, int), or truncate(long).

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

Informational metadata about whether this dialect is known to support specifying timeouts for requested lock acquisitions.

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

Does this dialect support sequences?

Does this dialect support temporary tables?

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

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

Does this dialect support the UNIQUE column syntax?

The SQL literal value to which this database maps boolean values.

Typically dialects which support sequences can create a sequence with a single command. This is convenience form of getCreateSequenceStrings(String) 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(String).

Typically dialects which support sequences can drop a sequence with a single command. This is convenience form of getDropSequenceStrings(String) 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(String).