Package mondrian.spi.impl

Class ImpalaDialect

  • All Implemented Interfaces:
    Dialect
    public class ImpalaDialect
extends HiveDialect
    Dialect for Cloudera's Impala DB.
    Since:
    2/11/13
    Author:
    cboyden

    • Constructor Detail

      • ImpalaDialect

        public ImpalaDialect​(Connection connection)
              throws SQLException
        Creates an ImpalaDialect.
        Parameters:
        connection - Connection
        Throws:
        SQLException - on error

    • Method Detail

      • generateOrderByNulls

        protected String generateOrderByNulls​(String expr,
                                      boolean ascending,
                                      boolean collateNullsLast)
        Description copied from class: JdbcDialectImpl
        Generates SQL to force null values to collate last.

        This default implementation makes use of the ANSI SQL 1999 CASE-WHEN-THEN-ELSE in conjunction with IS NULL syntax. The resulting SQL will look something like this:

        CASE WHEN "expr" IS NULL THEN 0 ELSE 1 END

        You can override this method for a particular database to use something more efficient, like ISNULL().

        ANSI SQL provides the syntax "ASC/DESC NULLS LAST" and "ASC/DESC NULLS FIRST". If your database supports the ANSI syntax, implement this method by calling JdbcDialectImpl.generateOrderByNullsAnsi(java.lang.String, boolean, boolean).

        This method is only called from JdbcDialectImpl.generateOrderItem(String, boolean, boolean, boolean). Some dialects override that method and therefore never call this method.

        Overrides:
        generateOrderByNulls in class HiveDialect
        Parameters:
        expr - Expression.
        ascending - Whether ascending.
        collateNullsLast - Whether nulls should appear first or last.
        Returns:
        Expression to force null values to collate last or first.

      • generateOrderItem

        public String generateOrderItem​(String expr,
                                boolean nullable,
                                boolean ascending,
                                boolean collateNullsLast)
        Description copied from interface: Dialect
        Generates an item for an ORDER BY clause, sorting in the required direction, and ensuring that NULL values collate either before or after all non-NULL values, depending on the collateNullsLast parameter.
        Specified by:
        generateOrderItem in interface Dialect
        Overrides:
        generateOrderItem in class JdbcDialectImpl
        Parameters:
        expr - Expression
        nullable - Whether expression may have NULL values
        ascending - Whether to sort expression ascending
        collateNullsLast - Whether the null values should be sorted first or last.
        Returns:
        Expression modified so that NULL values collate last

      • allowsMultipleCountDistinct

        public boolean allowsMultipleCountDistinct()
        Description copied from interface: Dialect
        Returns whether this Dialect supports more than one distinct aggregation in the same query.

        In Derby 10.1,

        select couunt(distinct x) from t
        is OK, but
        select couunt(distinct x), count(distinct y) from t
        gives "Multiple DISTINCT aggregates are not supported at this time."
        Specified by:
        allowsMultipleCountDistinct in interface Dialect
        Overrides:
        allowsMultipleCountDistinct in class JdbcDialectImpl
        Returns:
        whether this Dialect supports more than one distinct aggregation in the same query

      • requiresOrderByAlias

        public boolean requiresOrderByAlias()
        Description copied from interface: Dialect
        Returns true if this Dialect can include expressions in the ORDER BY clause only by adding an expression to the SELECT clause and using its alias.

        For example, in such a dialect,

        SELECT x FROM t ORDER BY x + y
        would be illegal, but
        SELECT x, x + y AS z FROM t ORDER BY z
        would be legal.

        MySQL, DB2 and Ingres are examples of such dialects.

        Specified by:
        requiresOrderByAlias in interface Dialect
        Overrides:
        requiresOrderByAlias in class HiveDialect
        Returns:
        Whether this Dialect can include expressions in the ORDER BY clause only by adding an expression to the SELECT clause and using its alias

      • supportsGroupByExpressions

        public boolean supportsGroupByExpressions()
        Description copied from interface: Dialect
        Returns whether this Dialect supports expressions in the GROUP BY clause. Derby/Cloudscape and Infobright do not.
        Specified by:
        supportsGroupByExpressions in interface Dialect
        Overrides:
        supportsGroupByExpressions in class JdbcDialectImpl
        Returns:
        Whether this Dialect allows expressions in the GROUP BY clause

      • allowsSelectNotInGroupBy

        public boolean allowsSelectNotInGroupBy()
        Description copied from interface: Dialect
        Returns whether the database currently permits queries to include in the SELECT clause expressions that are not listed in the GROUP BY clause. The SQL standard allows this if the database can deduce that the expression is functionally dependent on columns in the GROUP BY clause.

        For example, SELECT empno, first_name || ' ' || last_name FROM emps GROUP BY empno is valid because empno is the primary key of the emps table, and therefore all columns are dependent on it. For a given value of empno, first_name || ' ' || last_name has a unique value.

        Most databases do not, MySQL is an example of one that does (if the functioality is enabled).

        Specified by:
        allowsSelectNotInGroupBy in interface Dialect
        Overrides:
        allowsSelectNotInGroupBy in class JdbcDialectImpl
        Returns:
        Whether this Dialect allows SELECT clauses to contain columns that are not in the GROUP BY clause

      • generateInline

        public String generateInline​(List<String> columnNames,
                             List<String> columnTypes,
                             List<String[]> valueList)
        Description copied from interface: Dialect
        Generates a SQL statement to represent an inline dataset.

        For example, for Oracle, generates 

         SELECT 1 AS FOO, 'a' AS BAR FROM dual
 UNION ALL
 SELECT 2 AS FOO, 'b' AS BAR FROM dual

        For ANSI SQL, generates: 

         VALUES (1, 'a'), (2, 'b')
        Specified by:
        generateInline in interface Dialect
        Overrides:
        generateInline in class HiveDialect
        Parameters:
        columnNames - List of column names
        columnTypes - List of column types ("String" or "Numeric")
        valueList - List of rows values
        Returns:
        SQL string

      • allowsJoinOn

        public boolean allowsJoinOn()
        Description copied from interface: Dialect
        Returns whether this dialect supports "ANSI-style JOIN syntax", FROM leftTable JOIN rightTable ON conditon.
        Specified by:
        allowsJoinOn in interface Dialect
        Overrides:
        allowsJoinOn in class HiveDialect
        Returns:
        Whether this dialect supports FROM-JOIN-ON syntax.

      • quoteStringLiteral

        public void quoteStringLiteral​(StringBuilder buf,
                               String value)
        Description copied from interface: Dialect
        Appends to a buffer a single-quoted SQL string.

        For example, in the default dialect, quoteStringLiteral(buf, "Can't") appends "'Can''t'" to buf.

        Specified by:
        quoteStringLiteral in interface Dialect
        Overrides:
        quoteStringLiteral in class JdbcDialectImpl
        Parameters:
        buf - Buffer to append to
        value - Literal

      • generateRegularExpression

        public String generateRegularExpression​(String source,
                                        String javaRegex)
        Description copied from interface: Dialect
        Must generate a String representing a regular expression match operation between a string literal and a Java regular expression. The string literal might be a column identifier or some other identifier, but the implementation must presume that it is already escaped and fit for use. The regular expression is not escaped and must be adapted to the proper dialect rules.

        Postgres / Greenplum example:

        generateRegularExpression( "'foodmart'.'customer_name'", "(?i).*oo.*") -> 'foodmart'.'customer_name' ~ "(?i).*oo.*"

        Oracle example:

        generateRegularExpression( "'foodmart'.'customer_name'", ".*oo.*") -> REGEXP_LIKE('foodmart'.'customer_name', ".*oo.*")

        Dialects are allowed to return null if the dialect cannot convert that particular regular expression into something that the database would support.

        Specified by:
        generateRegularExpression in interface Dialect
        Overrides:
        generateRegularExpression in class JdbcDialectImpl
        Parameters:
        source - A String identifying the column to match against.
        javaRegex - A Java regular expression to match against.
        Returns:
        A dialect specific matching operation, or null if the dialect cannot convert that particular regular expression into something that the database would support.

      • allowsDdl

        public boolean allowsDdl()
        Description copied from interface: Dialect
        Returns whether this dialect supports common SQL Data Definition Language (DDL) statements such as CREATE TABLE and DROP INDEX.

        Access seems to allow DDL iff the .mdb file is writeable.

        Specified by:
        allowsDdl in interface Dialect
        Overrides:
        allowsDdl in class JdbcDialectImpl
        Returns:
        whether this Dialect supports DDL
        See Also:
        DatabaseMetaData.isReadOnly()