Github user dongjoon-hyun commented on a diff in the pull request: https://github.com/apache/spark/pull/15664#discussion_r94177466 --- Diff: sql/core/src/main/scala/org/apache/spark/sql/execution/datasources/jdbc/JdbcUtils.scala --- @@ -211,6 +211,55 @@ object JdbcUtils extends Logging { } /** + * Returns the schema if the table already exists in the JDBC database. + */ + def getSchema(conn: Connection, url: String, table: String): Option[StructType] = { + val dialect = JdbcDialects.get(url) + + try { + val statement = conn.prepareStatement(dialect.getSchemaQuery(table)) + try { + Some(getSchema(statement.executeQuery(), dialect)) + } catch { + case _: SQLException => None + } finally { + statement.close() + } + } catch { + case _: SQLException => None + } + } + + /** + * Returns a schema using rddSchema's column sequence and tableSchema's column names. + * + * When appending data into some case-sensitive DBMSs like PostgreSQL/Oracle, we need to respect + * the existing case-sensitive column names instead of RDD column names for user convenience. + * See SPARK-18123 for more details. + */ + def normalizeSchema( + rddSchema: StructType, + tableSchema: StructType, + caseSensitive: Boolean): StructType = { + val nameMap = tableSchema.fields.map(f => f.name -> f).toMap + val lowercaseNameMap = tableSchema.fields.map(f => f.name.toLowerCase -> f).toMap + + var schema = new StructType() + rddSchema.fields.foreach { f => + if (nameMap.isDefinedAt(f.name)) { + // identical names + schema = schema.add(nameMap(f.name)) + } else if (!caseSensitive && lowercaseNameMap.isDefinedAt(f.name.toLowerCase)) { + // identical names in a case-insensitive way + schema = schema.add(lowercaseNameMap(f.name.toLowerCase)) + } else { + throw new AnalysisException(s"""Column "${f.name}" not found""") --- End diff -- Oh, it's already in @gatorsmile 's patch. ``` throw new AnalysisException(s"""Column "${col.name}" not found in schema $tableSchema""") ```
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