[GitHub] [spark] sadikovi commented on a diff in pull request #40134: [SPARK-42534][SQL] Fix DB2Dialect Limit clause

["sadikovi (via GitHub)" <gi...@apache.org>]

sadikovi commented on code in PR #40134:
URL: https://github.com/apache/spark/pull/40134#discussion_r1115208845


##########
sql/core/src/test/scala/org/apache/spark/sql/jdbc/JDBCSuite.scala:
##########
@@ -1028,6 +1028,19 @@ class JDBCSuite extends QueryTest with SharedSparkSession {
       "SELECT TOP (123) a,b FROM test")
   }
 
+  test("SPARK-42534: DB2Dialect Limit query test") {
+    // JDBC url is a required option but is not used in this test.
+    val options = new JDBCOptions(Map("url" -> "jdbc:db2://host:port", "dbtable" -> "test"))
+    assert(
+      DB2Dialect
+        .getJdbcSQLQueryBuilder(options)
+        .withColumns(Array("a", "b"))
+        .withLimit(123)
+        .build()
+        .trim() ==
+      "SELECT a,b FROM test     FETCH FIRST 123 ROWS ONLY")

Review Comment:
   Yes, I do. This is because of the string interpolation for the JDBC query that is written like `"$a $b $c...`. So when some of the components are empty, whitespaces are still kept between the components resulting in the long gaps.
   
   ```scala
   options.prepareQuery +
         s"SELECT $myTopExpression $columnList FROM ${options.tableOrQuery} $myTableSampleClause" +
         s" $myWhereClause $getGroupByClause $getOrderByClause $myLimitClause $myOffsetClause"
   ```
   
   https://github.com/apache/spark/blob/4b50a46f1c6ba4ffe2c42f70a512879c28d11dcf/sql/core/src/main/scala/org/apache/spark/sql/jdbc/JdbcSQLQueryBuilder.scala#L163.



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