ClickHouse/src/Interpreters/ColumnAliasesVisitor.h

#pragma once

#include <Core/Names.h>
#include <Interpreters/InDepthNodeVisitor.h>
#include <Storages/ColumnsDescription.h>

namespace DB
{

class IAST;
using ASTPtr = std::shared_ptr<IAST>;
class IDataType;
class ASTFunction;
class ASTIdentifier;
using DataTypePtr = std::shared_ptr<const IDataType>;

/// Visits AST node to rewrite alias columns in query
/// Currently works only 3 kind ways below

/// For example:
//    CREATE TABLE test_table
//    (
//     `timestamp` DateTime,
//     `value` UInt64,
//     `day` Date ALIAS toDate(timestamp),
//     `day1` Date ALIAS day + 1,
//     `day2` Date ALIAS day1 + 1,
//     `time` DateTime ALIAS timestamp
//    )ENGINE = MergeTree
//    PARTITION BY toYYYYMMDD(timestamp)
//    ORDER BY timestamp SETTINGS index_granularity = 1;

/// 1. Rewrite the filters in query when enable optimize_respect_aliases
///  this could help with `optimize_trivial_count`, Partition Prune in `KeyCondition` and secondary indexes.
///  eg: select max(value) from test_table where day2 = today(), filters will be: ((toDate(timestamp) + 1) + 1) = today() .

/// 2. Alias on alias for `required_columns` extracted in `InterpreterSelectQuery.cpp`, it could help get all dependent physical columns for query.
///  eg: select day2 from test_table. `required_columns` can got require columns from the temporary rewritten AST `((toDate(timestamp) + 1) + 1)`.

/// 3. Help with `optimize_aggregation_in_order` and `optimize_read_in_order` in `ReadInOrderOptimizer.cpp`:
///    For queries with alias columns in `orderBy` and `groupBy`, these ASTs will not change.
///    But we generate temporary asts and generate temporary Actions to get the `InputOrderInfo`
///  eg: select day1 from test_table order by day1;


class ColumnAliasesMatcher
{
public:
    using Visitor = InDepthNodeVisitor<ColumnAliasesMatcher, false>;

    struct Data
    {
        const ColumnsDescription & columns;

        /// forbidden_columns are from array join, we can't rewrite alias columns involved in array join.
        /// Do not analyze joined columns.
        /// They may have aliases and come to description as is.
        const NameSet & forbidden_columns;
        ContextPtr context;

        /// private_aliases are from lambda, so these are local names.
        NameSet private_aliases;

        Data(const ColumnsDescription & columns_, const NameSet & forbidden_columns_, ContextPtr context_)
        : columns(columns_)
        , forbidden_columns(forbidden_columns_)
        , context(context_)
        {}
    };

    static void visit(ASTPtr & ast, Data & data);
    static bool needChildVisit(const ASTPtr & node, const ASTPtr & child);

private:
    static void visit(ASTIdentifier & node, ASTPtr & ast, Data & data);
    static void visit(ASTFunction & node, ASTPtr & ast, Data & data);
};

using ColumnAliasesVisitor = ColumnAliasesMatcher::Visitor;

}