PetarVasiljevic-DB commented on code in PR #48625:
URL: https://github.com/apache/spark/pull/48625#discussion_r1822568499


##########
sql/core/src/main/scala/org/apache/spark/sql/jdbc/PostgresDialect.scala:
##########
@@ -382,18 +382,45 @@ private case class PostgresDialect()
       case Types.ARRAY =>
         val tableName = rsmd.getTableName(columnIdx)
         val columnName = rsmd.getColumnName(columnIdx)
-        val query =
-          s"""
-             |SELECT pg_attribute.attndims
-             |FROM pg_attribute
-             |  JOIN pg_class ON pg_attribute.attrelid = pg_class.oid
-             |  JOIN pg_namespace ON pg_class.relnamespace = pg_namespace.oid
-             |WHERE pg_class.relname = '$tableName' and pg_attribute.attname = 
'$columnName'
-             |""".stripMargin
+
+        /*
+         Spark does not support different dimensionality per row, therefore we 
retrieve the
+         dimensionality of any row from Postgres. This might fail later on as 
Postgres allows
+         different dimensions per row for arrays.
+         */
+        val query = s"SELECT array_ndims($columnName) FROM $tableName LIMIT 1"
+        var arrayDimensionalityResolveNeedsFallback = true
+
         try {
           Using.resource(conn.createStatement()) { stmt =>
             Using.resource(stmt.executeQuery(query)) { rs =>
-              if (rs.next()) metadata.putLong("arrayDimension", rs.getLong(1))
+              if (rs.next()) {
+                metadata.putLong("arrayDimension", rs.getLong(1))
+                arrayDimensionalityResolveNeedsFallback = false
+              }
+            }
+          }
+
+          if (arrayDimensionalityResolveNeedsFallback) {

Review Comment:
   I thought it would be cleaner than using additional nesting of 
`Using.resource...`. so I introduced `arrayDimensionalityResolveNeedsFallback`. 
I have refactored now.



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