From cdadef78471b47d05d6d1c437a823b17f8867991 Mon Sep 17 00:00:00 2001
From: Vitaly Baranov <vitlibar@clickhouse.com>
Date: Thu, 18 Jul 2024 21:26:33 +0200
Subject: [PATCH] Add more comments.

---
 src/Parsers/ASTViewTargets.h    | 21 +++++++++++++++++----
 src/Parsers/ParserViewTargets.h |  7 ++++++-
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/src/Parsers/ASTViewTargets.h b/src/Parsers/ASTViewTargets.h
index 33a7bc5fcb1..12182919f0e 100644
--- a/src/Parsers/ASTViewTargets.h
+++ b/src/Parsers/ASTViewTargets.h
@@ -9,15 +9,20 @@ namespace DB
 class ASTStorage;
 enum class Keyword : size_t;
 
-/// Information about the target table for a materialized view or a window view.
+/// Information about target tables (external or inner) of a materialized view or a window view.
+/// See ASTViewTargets for more details.
 struct ViewTarget
 {
     enum Kind
     {
-        /// Target table for a materialized view or a window view.
+        /// If `kind == ViewTarget::To` then `ViewTarget` contains information about the "TO" table of a materialized view or a window view:
+        ///     CREATE MATERIALIZED VIEW db.mv_name {TO [db.]to_target | ENGINE to_engine} AS SELECT ...
+        /// or
+        ///     CREATE WINDOW VIEW db.wv_name {TO [db.]to_target | ENGINE to_engine} AS SELECT ...
         To,
 
-        /// Table with intermediate results for a window view.
+        /// If `kind == ViewTarget::Inner` then `ViewTarget` contains information about the "INNER" table of a window view:
+        ///     CREATE WINDOW VIEW db.wv_name {INNER ENGINE inner_engine} AS SELECT ...
         Inner,
     };
 
@@ -42,7 +47,15 @@ std::string_view toString(ViewTarget::Kind kind);
 void parseFromString(ViewTarget::Kind & out, std::string_view str);
 
 
-/// Information about all the target tables for a view.
+/// Information about all target tables (external or inner) of a view.
+///
+/// For example, for a materialized view:
+///     CREATE MATERIALIZED VIEW db.mv_name [TO [db.]to_target | ENGINE to_engine] AS SELECT ...
+/// this class contains information about the "TO" table: its name and database (if it's external), its UUID and engine (if it's inner).
+///
+/// For a window view:
+///     CREATE WINDOW VIEW db.wv_name [TO [db.]to_target | ENGINE to_engine] [INNER ENGINE inner_engine] AS SELECT ...
+/// this class contains information about both the "TO" table and the "INNER" table.
 class ASTViewTargets : public IAST
 {
 public:
diff --git a/src/Parsers/ParserViewTargets.h b/src/Parsers/ParserViewTargets.h
index f5d1850e974..3af3c0b8df3 100644
--- a/src/Parsers/ParserViewTargets.h
+++ b/src/Parsers/ParserViewTargets.h
@@ -7,7 +7,12 @@
 namespace DB
 {
 
-/// Parses information about target views of a table.
+/// Parses information about target tables (external or inner) of a materialized view or a window view.
+/// The function parses one or multiple parts of a CREATE query looking like this:
+///     TO db.table_name
+///     TO INNER UUID 'XXX'
+///     {ENGINE / INNER ENGINE} TableEngine(arguments) [ORDER BY ...] [SETTINGS ...]
+/// Returns ASTViewTargets if succeeded.
 class ParserViewTargets : public IParserBase
 {
 public: