chore: fixed additional review comments and added docs for the node

Author: mzabuawala

docs/en_US/managing_database_objects.rst

@@ -39,6 +39,7 @@ node, and select *Create Cast...*
    publication_dialog
    schema_dialog
    sequence_dialog
+   statistics_dialog
    subscription_dialog
    synonym_dialog
    trigger_function_dialog

docs/en_US/release_notes_9_16.rst

@@ -29,6 +29,7 @@ New features
   | `Issue #9626 <https://github.com/pgadmin-org/pgadmin4/issues/9626>`_ -  Add support for the TOAST tuple target storage parameter in the Materialized View dialog.
   | `Issue #9646 <https://github.com/pgadmin-org/pgadmin4/issues/9646>`_ -  Make the init container security context in the Helm chart configurable via containerSecurityContext, consistent with the main container.
   | `Issue #9699 <https://github.com/pgadmin-org/pgadmin4/issues/9699>`_ -  Add support for closing a tab with a middle-click on its title.
+  | `Issue #2018 <https://github.com/pgadmin-org/pgadmin4/issues/2018>`_ -  Added support for Extended Statistics objects (CREATE STATISTICS) under the Schema node, with full create, edit, delete, and SQL-generation support for column-based and expression-based statistics on PostgreSQL 14+.
 
 Housekeeping
 ************

docs/en_US/statistics_dialog.rst

@@ -0,0 +1,67 @@
+.. _statistics_dialog:
+
+**************************
+`Statistics Dialog`:index:
+**************************
+
+Use the *Statistics* dialog to define extended statistics on one or more columns
+(or expressions) of a table. Extended statistics let PostgreSQL collect
+correlation data across columns that can significantly improve query-plan
+estimates for queries that filter or group by multiple columns.
+
+Extended statistics require PostgreSQL 14 or later.
+
+The *Statistics* dialog organizes options across the *General* and *Definition*
+tabs. The *SQL* tab displays the SQL command generated by your selections.
+
+Use the fields in the *General* tab to identify the statistics object:
+
+* Use the *Name* field to enter a descriptive name. On PostgreSQL 16 and later,
+  the name is optional — PostgreSQL will auto-generate one if left blank.
+* Use the *Owner* field to select the role that will own the statistics object.
+* Use the *Schema* field to select the schema in which the statistics object
+  will reside.
+* Use the *Comment* field to store an optional note about the statistics object.
+
+Click the *Definition* tab to continue.
+
+Use the fields in the *Definition* tab to describe the statistics:
+
+* Use the *Table* field to select the table on which the statistics will be
+  collected. The list is filtered to tables in the selected schema.
+* Use the *Columns* field to select two or more columns. Hold *Ctrl* (or *Cmd*
+  on macOS) to select multiple columns. At least two columns are required when
+  collecting column-based statistics.
+* Use the *Expressions* field to enter one or more SQL expressions separated by
+  commas (e.g. ``lower(col1), (col1 + col2)``). Specify expressions instead of
+  columns when you want statistics on derived values.
+* Use the *Statistics types* field to choose which kinds of extended statistics
+  to collect:
+
+  * *N-distinct* — estimates the number of distinct value combinations across
+    the selected columns or expressions.
+  * *Dependencies* — detects functional dependencies between columns, improving
+    estimates for queries with correlated ``WHERE`` clauses.
+  * *MCV (Most Common Values)* — records the most common combinations of values,
+    available on PostgreSQL 12 and later.
+
+Click the *SQL* tab to continue.
+
+Your entries in the *Statistics* dialog generate a SQL command (see an example
+below). Use the *SQL* tab for review; revisit or switch tabs to make any changes.
+
+Example
+*******
+
+The following is an example of the SQL command generated by user selections in
+the *Statistics* dialog::
+
+    CREATE STATISTICS public.order_stats
+        (ndistinct, dependencies)
+        ON customer_id, region_id
+        FROM public.orders;
+
+* Click the *Info* button (i) to access online help.
+* Click the *Save* button to save work.
+* Click the *Close* button to exit without saving work.
+* Click the *Reset* button to restore configuration parameters.

web/pgadmin/browser/server_groups/servers/databases/schemas/statistics/__init__.py

@@ -363,12 +363,9 @@ def _fetch_properties(self, scid, stid):
         if row.get('columns') is None:
             row['columns'] = []
 
-        # Set has_expressions boolean based on expressions field
-        # expressions is pg_node_tree (bytea) - we just check if it exists
-        row['has_expressions'] = row.get('expressions') is not None
-
-        # Remove expressions from display (it's internal PostgreSQL format)
-        row.pop('expressions', None)
+        # expression_list is the deparsed text from pg_get_expr; keep it for
+        # SQL-tab round-trip and set has_expressions for the properties switch
+        row['has_expressions'] = row.get('expression_list') is not None
 
         # Ensure stattarget has a default value if None
         if row.get('stattarget') is None:

web/pgadmin/browser/server_groups/servers/databases/schemas/statistics/static/js/statistics.ui.js

@@ -116,7 +116,9 @@ export default class StatisticsSchema extends BaseUISchema {
           let tid = obj.getTableOid(state.table);
           return {
             type: 'select',
-            options: state.table ? ()=>obj.fieldOptions.getColumns({tid: tid}) : [],
+            options: (state.table && tid)
+              ? () => obj.fieldOptions.getColumns({tid: tid})
+              : (state.columns || []).map(col => ({label: col, value: col})),
             optionsReloadBasis: state.table,
           };
         },

web/pgadmin/browser/server_groups/servers/databases/schemas/statistics/templates/statistics/sql/16_plus/create.sql

@@ -4,7 +4,7 @@ CREATE STATISTICS{% if data.name %}{% if add_not_exists_clause %} IF NOT EXISTS{
 
     ({% for stype in data.stat_types %}{{ stype }}{% if not loop.last %}, {% endif %}{% endfor %}){% endif %}
 
-    ON {% if data.expressions and data.expressions|length > 0 %}{% for expr in data.expressions %}({{ expr.expression if expr.expression is defined else expr }}){% if not loop.last %}, {% endif %}{% endfor %}{% elif data.columns %}{% for col in data.columns %}{{ conn|qtIdent(col) }}{% if not loop.last %}, {% endif %}{% endfor %}{% endif %}
+    ON {% if data.expressions and data.expressions|length > 0 %}{% for expr in data.expressions %}({{ expr.expression if expr.expression is defined else expr }}){% if not loop.last %}, {% endif %}{% endfor %}{% elif data.expression_list %}{{ data.expression_list }}{% elif data.columns %}{% for col in data.columns %}{{ conn|qtIdent(col) }}{% if not loop.last %}, {% endif %}{% endfor %}{% endif %}
 
     FROM {{ conn|qtIdent(data.schema, data.table) }};
 {% if data.comment and data.name %}

web/pgadmin/browser/server_groups/servers/databases/schemas/statistics/templates/statistics/sql/16_plus/properties.sql

@@ -20,7 +20,7 @@ SELECT
     CASE WHEN 'm' = ANY(s.stxkind) THEN true ELSE false END AS has_mcv,
     s.stxstattarget AS stattarget,
 {### stxexprs added in PostgreSQL 14 for expression statistics ###}
-    s.stxexprs AS expressions,
+    pg_catalog.pg_get_expr(s.stxexprs, s.stxrelid) AS expression_list,
 {### Statistics data from pg_statistic_ext_data (PostgreSQL 12+) ###}
     sd.stxdndistinct AS ndistinct_values,
     sd.stxddependencies AS dependencies_values,

web/pgadmin/browser/server_groups/servers/databases/schemas/statistics/templates/statistics/sql/16_plus/update.sql

@@ -1,8 +1,7 @@
 {### SQL to update extended statistics object (PostgreSQL 16+) ###}
 {### Rename statistics ###}
 {% if data.name and data.name != o_data.name %}
-ALTER STATISTICS {% if data.schema and data.schema != o_data.schema %}{{ conn|qtIdent(o_data.schema, o_data.name) }}{% else %}{{ conn|qtIdent(o_data.schema, o_data.name) }}{% endif %}
-
+ALTER STATISTICS {{ conn|qtIdent(o_data.schema, o_data.name) }}
     RENAME TO {{ conn|qtIdent(data.name) }};
 
 {% endif %}

web/pgadmin/browser/server_groups/servers/databases/schemas/statistics/templates/statistics/sql/17_plus/create.sql

@@ -4,7 +4,7 @@ CREATE STATISTICS{% if data.name %}{% if add_not_exists_clause %} IF NOT EXISTS{
 
     ({% for stype in data.stat_types %}{{ stype }}{% if not loop.last %}, {% endif %}{% endfor %}){% endif %}
 
-    ON {% if data.expressions and data.expressions|length > 0 %}{% for expr in data.expressions %}({{ expr.expression if expr.expression is defined else expr }}){% if not loop.last %}, {% endif %}{% endfor %}{% elif data.columns %}{% for col in data.columns %}{{ conn|qtIdent(col) }}{% if not loop.last %}, {% endif %}{% endfor %}{% endif %}
+    ON {% if data.expressions and data.expressions|length > 0 %}{% for expr in data.expressions %}({{ expr.expression if expr.expression is defined else expr }}){% if not loop.last %}, {% endif %}{% endfor %}{% elif data.expression_list %}{{ data.expression_list }}{% elif data.columns %}{% for col in data.columns %}{{ conn|qtIdent(col) }}{% if not loop.last %}, {% endif %}{% endfor %}{% endif %}
 
     FROM {{ conn|qtIdent(data.schema, data.table) }};
 {% if data.comment and data.name %}

web/pgadmin/browser/server_groups/servers/databases/schemas/statistics/templates/statistics/sql/17_plus/properties.sql

@@ -20,7 +20,7 @@ SELECT
     CASE WHEN 'm' = ANY(s.stxkind) THEN true ELSE false END AS has_mcv,
     s.stxstattarget AS stattarget,
 {### stxexprs added in PostgreSQL 14 for expression statistics ###}
-    s.stxexprs AS expressions,
+    pg_catalog.pg_get_expr(s.stxexprs, s.stxrelid) AS expression_list,
 {### Statistics data from pg_statistic_ext_data (PostgreSQL 12+) ###}
     sd.stxdndistinct AS ndistinct_values,
     sd.stxddependencies AS dependencies_values,