ClickHouse SQL Parser

The goal of this project is to build a ClickHouse SQL parser in Go with the following key features:

• Parse ClickHouse SQL into AST
• Beautify ClickHouse SQL format

This project is inspired by memefish which is a SQL parser for Spanner in Go.

How to use

You can use it as your Go library or CLI tool, see the following examples:

• Use clickhouse-sql-parser as a Go library

package main

import (
    clickhouse "github.com/AfterShip/clickhouse-sql-parser/parser"
)

query := "SELECT * FROM clickhouse"
parser := clickhouse.NewParser(query)
// Parse query into AST
statements, err := parser.ParseStmts()
if err != nil {
    return nil, err
}

• Install clickhouse-sql-parser as a CLI tool

On Linux:

$ go install github.com/AfterShip/clickhouse-sql-parser@latest

On macOS:

$ brew install clickhouse-sql-parser

Parse ClickHouse SQL into AST or format ClickHouse SQL:

## Parse query into AST
$ clickhouse-sql-parser "SELECT * FROM clickhouse WHERE a=100"

## Format query (compact, single-line output)
$ clickhouse-sql-parser -format "SELECT * FROM clickhouse WHERE a=100"

## Beautify query (formatted with proper indentation and line breaks)
$ clickhouse-sql-parser -beautify "SELECT * FROM clickhouse WHERE a=100"

## Parse query from file
$ clickhouse-sql-parser -f ./test.sql

Beautify SQL Example

The -beautify flag formats SQL with proper indentation and line breaks, making complex queries more readable:

# Input (compact, hard to read)
$ clickhouse-sql-parser -beautify "SELECT user_id, COUNT(*) AS total, AVG(amount) AS avg_amount FROM orders WHERE status='completed' AND created_at>'2024-01-01' GROUP BY user_id HAVING COUNT(*)>5 ORDER BY total DESC LIMIT 10"

# Output (beautified, easy to read)
SELECT
  user_id,
  COUNT(*) AS total,
  AVG(amount) AS avg_amount
FROM orders
WHERE
  status = 'completed'
AND
  created_at > '2024-01-01'
GROUP BY
  user_id
HAVING COUNT(*) > 5
ORDER BY
  total DESC
LIMIT 10

• Parsed tree(AST) back into a SQL statement

parser := clickhouse.NewParser("SELECT * FROM clickhouse")
// Parse query into AST
statements, err := parser.ParseStmts()
if err != nil {
    return nil, err
}

// Format AST back into a SQL string
for _, stmt := range statements {
  fmt.Println(clickhouse.Format(stmt))
}

AST Traversal

Walk Pattern (Recommended)

The Walk pattern provides a simple and efficient way to traverse AST nodes. Use the Walk function to visit all nodes in the AST:

import (
    clickhouse "github.com/AfterShip/clickhouse-sql-parser/parser"
)

parser := clickhouse.NewParser("SELECT * FROM table WHERE id = 1")
statements, err := parser.ParseStmts()
if err != nil {
    return err
}

// Walk through all nodes in the AST
clickhouse.Walk(statements[0], func(node clickhouse.Expr) bool {
    fmt.Printf("Node type: %T\n", node)
    return true // return false to stop traversal for this subtree
})

Walk Pattern Functions

• Walk(node Expr, fn WalkFunc) - Traverses all nodes in depth-first order
• WalkWithBreak(node Expr, fn WalkFunc) - Allows early termination of traversal
• Find(root Expr, predicate func(Expr) bool) - Finds the first node matching a condition
• FindAll(root Expr, predicate func(Expr) bool) - Finds all nodes matching a condition
• Transform(root Expr, transformer func(Expr) Expr) - Applies transformations to nodes

Examples

Find all table identifiers:

tables := clickhouse.FindAll(stmt, func(node clickhouse.Expr) bool {
    _, ok := node.(*clickhouse.TableIdentifier)
    return ok
})

Find the first WHERE clause:

whereClause, found := clickhouse.Find(stmt, func(node clickhouse.Expr) bool {
    _, ok := node.(*clickhouse.WhereClause)
    return ok
})

Update test assets

For the files inside output and format dir are generated by the test cases,

if you want to update them, you can run the following command:

$ make update_test

Benchmarks

go test -bench=. -benchmem ./parser

Results

$ go test -bench=. -benchmem ./parser
goos: linux
goarch: amd64
pkg: github.com/AfterShip/clickhouse-sql-parser/parser
cpu: Intel(R) Xeon(R) CPU E5-2697 v3 @ 2.60GHz
BenchmarkParseSQLFiles/access_tuple_with_dot.sql-28                23294             58467 ns/op           13448 B/op        293 allocs/op
BenchmarkParseSQLFiles/query_with_expr_compare.sql-28              43560             25704 ns/op            6240 B/op        132 allocs/op
BenchmarkParseSQLFiles/select_cast.sql-28                          75055             16518 ns/op            4648 B/op         92 allocs/op
BenchmarkParseSQLFiles/select_column_alias_string.sql-28          499798              2785 ns/op             704 B/op         13 allocs/op
BenchmarkParseSQLFiles/select_expr.sql-28                         488187              2448 ns/op             696 B/op         12 allocs/op
BenchmarkParseSQLFiles/select_item_with_modifiers.sql-28           54124             23305 ns/op            6232 B/op        136 allocs/op
BenchmarkParseSQLFiles/select_order_by_timestamp.sql-28           232302              5809 ns/op            1368 B/op         28 allocs/op
BenchmarkParseSQLFiles/select_simple.sql-28                        30602             50022 ns/op            9920 B/op        216 allocs/op
BenchmarkParseSQLFiles/select_simple_field_alias.sql-28           178126              6316 ns/op            1712 B/op         39 allocs/op
BenchmarkParseSQLFiles/select_simple_with_bracket.sql-28           71902             16172 ns/op            3824 B/op         85 allocs/op
BenchmarkParseSQLFiles/select_simple_with_cte_with_column_aliases.sql-28                   67050             19916 ns/op            4648 B/op        101 allocs/op
BenchmarkParseSQLFiles/select_simple_with_group_by_with_cube_totals.sql-28                107047             10348 ns/op            2768 B/op         58 allocs/op
BenchmarkParseSQLFiles/select_simple_with_is_not_null.sql-28                               55285             21957 ns/op            5224 B/op        111 allocs/op
BenchmarkParseSQLFiles/select_simple_with_is_null.sql-28                                   66648             22412 ns/op            4728 B/op        102 allocs/op
BenchmarkParseSQLFiles/select_simple_with_top_clause.sql-28                               269910              4166 ns/op            1088 B/op         22 allocs/op
BenchmarkParseSQLFiles/select_simple_with_with_clause.sql-28                               58494             18417 ns/op            5144 B/op        109 allocs/op
BenchmarkParseSQLFiles/select_table_alias_without_keyword.sql-28                          121261             10011 ns/op            2896 B/op         65 allocs/op
BenchmarkParseSQLFiles/select_table_function_with_query.sql-28                             98017             14929 ns/op            4168 B/op         81 allocs/op
BenchmarkParseSQLFiles/select_when_condition.sql-28                                       220394              5457 ns/op            1304 B/op         28 allocs/op
BenchmarkParseSQLFiles/select_with_distinct.sql-28                                        172948              6531 ns/op            1560 B/op         33 allocs/op
BenchmarkParseSQLFiles/select_with_join_only.sql-28                                       286346              5594 ns/op            1520 B/op         32 allocs/op
BenchmarkParseSQLFiles/select_with_left_join.sql-28                                        88200             13627 ns/op            3880 B/op         75 allocs/op
BenchmarkParseSQLFiles/select_with_literal_table_name.sql-28                              241094              5099 ns/op            1304 B/op         27 allocs/op
BenchmarkParseSQLFiles/select_with_multi_join.sql-28                                       44700             31964 ns/op            8240 B/op        188 allocs/op
BenchmarkParseSQLFiles/select_with_multi_line_comment.sql-28                              363499              4460 ns/op             824 B/op         18 allocs/op
BenchmarkParseSQLFiles/select_with_multi_union.sql-28                                     146233              7827 ns/op            2176 B/op         36 allocs/op
BenchmarkParseSQLFiles/select_with_number_field.sql-28                                    129945              8746 ns/op            2352 B/op         51 allocs/op
BenchmarkParseSQLFiles/select_with_query_parameter.sql-28                                  33850             36346 ns/op            9936 B/op        209 allocs/op
BenchmarkParseSQLFiles/select_with_string_expr.sql-28                                     142882              7530 ns/op            1880 B/op         34 allocs/op
BenchmarkParseSQLFiles/select_with_union_distinct.sql-28                                  147031              9601 ns/op            2352 B/op         47 allocs/op
BenchmarkParseSQLFiles/select_with_variable.sql-28                                        179158              6669 ns/op            1880 B/op         36 allocs/op
BenchmarkParseSQLFiles/select_with_window_function.sql-28                                  54925             31320 ns/op            6720 B/op        136 allocs/op
BenchmarkParseSQLFiles/select_with_placeholder.sql-28                                    196771              5145 ns/op            1272 B/op         26 allocs/op
BenchmarkParseSQLFiles/set_simple.sql-28                                                  172419              7062 ns/op            2480 B/op         49 allocs/op
BenchmarkParseComplexQueries/testdata/query/select_with_multi_join.sql-28                  39056             36897 ns/op            8240 B/op        188 allocs/op
BenchmarkParseComplexQueries/testdata/query/select_with_window_function.sql-28             47629             29916 ns/op            6720 B/op        136 allocs/op
BenchmarkParseComplexQueries/testdata/query/select_simple_with_with_clause.sql-28                  69210             19731 ns/op            5144 B/op        109 allocs/op
BenchmarkParseComplexQueries/testdata/query/select_with_left_join.sql-28                           74576             15338 ns/op            3880 B/op         75 allocs/op
BenchmarkParseComplexQueries/testdata/benchdata/posthog_huge_0.sql-28                                235           6231253 ns/op         1236189 B/op      26696 allocs/op
BenchmarkParseComplexQueries/testdata/benchdata/posthog_huge_1.sql-28                                279           4438280 ns/op         1043374 B/op      22717 allocs/op
PASS
ok      github.com/AfterShip/clickhouse-sql-parser/parser       66.547s

Contact us

Feel free to open an issue or discussion if you have any issues or questions.