[GitHub] [hive] kasakrisz commented on a change in pull request #2752: HIVE-25652: Add constraints in result of “SHOW CREATE TABLE ”

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kasakrisz commented on a change in pull request #2752:
URL: https://github.com/apache/hive/pull/2752#discussion_r739999468



##########
File path: ql/src/java/org/apache/hadoop/hive/ql/exec/DDLPlanUtils.java
##########
@@ -800,19 +804,59 @@ private String getExternal(Table table) {
     return table.getTableType() == TableType.EXTERNAL_TABLE ? "EXTERNAL " : "";
   }
 
-  private String getColumns(Table table) {
-    List<String> columnDescs = new ArrayList<String>();
+  private String getColumns(Table table) throws HiveException{
+    List<String> columnDescs = new ArrayList<>();
+    Set<String> notNullColumns = null;
+    if (NotNullConstraint.isNotNullConstraintNotEmpty(table.getNotNullConstraint())) {
+      notNullColumns = new HashSet<>(table.getNotNullConstraint().getNotNullConstraints().values());
+    }
+
+    Map<String, String> columnDefaultValueMap = null;
+    if (DefaultConstraint.isCheckConstraintNotEmpty(table.getDefaultConstraint())) {
+      columnDefaultValueMap = table.getDefaultConstraint().getColNameToDefaultValueMap();
+    }
     for (FieldSchema column : table.getCols()) {
       String columnType = formatType(TypeInfoUtils.getTypeInfoFromTypeString(column.getType()));
-      String columnDesc = "  `" + column.getName() + "` " + columnType;
+      String columnName = column.getName();
+      StringBuilder columnDesc = new StringBuilder();
+      columnDesc.append("  `").append(columnName).append("` ").append(columnType);

Review comment:
       Without backticks identifiers contains special characters like space can not be handled. See the create table example from `quotedid_basic.q` Those characters can be used in column names too.
   
   Yes, it requires a more complex solution but in the end we can print `CREATE TABLE` statements which can be executed by just copy-pasting.
   
   Probably the expression in the check constraint must be parsed to AST to collect the identifiers and replace them with the escaped versions.
   1. Example how to build the AST:
   https://github.com/apache/hive/blob/8a8e03d02003aa3543f46f595b4425fd8c156ad9/ql/src/java/org/apache/hadoop/hive/ql/parse/type/ConstraintExprGenerator.java#L180
   2. The AST need to be traversed to replace the identifiers.
   3. Print the altered expression from AST. You need a TokenRewriteStream to do this and currently `parseExpression` doesn't return it. So more code need to be changed 🙂  https://github.com/apache/hive/blob/8a8e03d02003aa3543f46f595b4425fd8c156ad9/ql/src/java/org/apache/hadoop/hive/ql/parse/SemanticAnalyzer.java#L15010
   
   This seems to be a bigger change feel free to tackle this in a separate jira.




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