[SPARK-54112][CONNECT] Support getSchemas for SparkConnectDatabaseMetaData

[pan3793]

What changes were proposed in this pull request?

Implement getSchemas methods defined in java.sql.DatabaseMetaData for SparkConnectDatabaseMetaData.

    /**
     * Retrieves the schema names available in this database.  The results
     * are ordered by {@code TABLE_CATALOG} and
     * {@code TABLE_SCHEM}.
     *
     * <P>The schema columns are:
     *  <OL>
     *  <LI><B>TABLE_SCHEM</B> String {@code =>} schema name
     *  <LI><B>TABLE_CATALOG</B> String {@code =>} catalog name (may be {@code null})
     *  </OL>
     *
     * @return a {@code ResultSet} object in which each row is a
     *         schema description
     * @throws SQLException if a database access error occurs
     *
     */
    ResultSet getSchemas() throws SQLException;

    /**
     * Retrieves the schema names available in this database.  The results
     * are ordered by {@code TABLE_CATALOG} and
     * {@code TABLE_SCHEM}.
     *
     * <P>The schema columns are:
     *  <OL>
     *  <LI><B>TABLE_SCHEM</B> String {@code =>} schema name
     *  <LI><B>TABLE_CATALOG</B> String {@code =>} catalog name (may be {@code null})
     *  </OL>
     *
     *
     * @param catalog a catalog name; must match the catalog name as it is stored
     * in the database;"" retrieves those without a catalog; null means catalog
     * name should not be used to narrow down the search.
     * @param schemaPattern a schema name; must match the schema name as it is
     * stored in the database; null means
     * schema name should not be used to narrow down the search.
     * @return a {@code ResultSet} object in which each row is a
     *         schema description
     * @throws SQLException if a database access error occurs
     * @see #getSearchStringEscape
     * @since 1.6
     */
    ResultSet getSchemas(String catalog, String schemaPattern) throws SQLException;

Why are the changes needed?

Enhance API coverage of the Connect JDBC driver, for example, get[Catalogs|Schemas|Tables|...] APIs are used by SQL GUI tools such as DBeaver for displaying the tree category.

Does this PR introduce any user-facing change?

No, Connect JDBC driver is a new feature under development.

How was this patch tested?

New UT is added, also tested via DBeaver - the catalog/schema tree works now.

Was this patch authored or co-authored using generative AI tooling?

No.

[pan3793]

This is used to test whether fooPattern matches ALL

https://docs.oracle.com/en/java/javase/17/docs/api/java.sql/java/sql/DatabaseMetaData.html

Some DatabaseMetaData methods take arguments that are String patterns. These arguments all have names such as fooPattern. Within a pattern String, "%" means match any substring of 0 or more characters, and "_" means match any one character. Only metadata entries matching the search pattern are returned. If a search pattern argument is set to null, that argument's criterion will be dropped from the search.

[pan3793]

this is ready for review, cc @LuciferYang

[dongjoon-hyun]

Gentle ping, @pan3793 .

[pan3793]

Spark SQL uses backslash as the default escape char for LIKE expression, it also supports custom escape char

https://spark.apache.org/docs/latest/sql-ref-syntax-qry-select-like.html

[ NOT ] { LIKE search_pattern [ ESCAPE esc_char ] | [ RLIKE | REGEXP ] regex_pattern }
...

...

• esc_char
  Specifies the escape character. The default escape character is .

[LuciferYang]

how about

    val schemaFilter = if (isNullOrWildcard(schemaPattern)) {
      lit(true)
    } else {
      col("TABLE_SCHEM").like(schemaPattern)
    }

[pan3793]

thank you for suggestion, this sounds better, addressed in 711f602

[dongjoon-hyun]

+1, LGTM (Pending CIs).

[dongjoon-hyun]

Merged to master/4.1 for Apache Spark 4.1.0. Thank you, @pan3793 and @LuciferYang .