feat: add ClickHouse database engine support

Add ClickHouse support using the github.com/sqlc-dev/doubleclick parser library.

New files in internal/engine/clickhouse/:
- parse.go: Parser implementation using doubleclick
- convert.go: AST converter from doubleclick to sqlc AST
- format.go: ClickHouse-specific SQL formatting
- catalog.go: Catalog initialization
- stdlib.go: Standard library functions
- reserved.go: Reserved keywords
- utils.go: Helper functions
- parse_test.go: Unit tests

Supported SQL operations:
- SELECT with JOINs, subqueries, CTEs, window functions
- INSERT with VALUES and SELECT subquery
- UPDATE and DELETE
- CREATE TABLE, ALTER TABLE, DROP TABLE, TRUNCATE

Co-Authored-By: Claude <noreply@anthropic.com>

Author: kyleconroy

go.mod

@@ -1,8 +1,6 @@
 module github.com/sqlc-dev/sqlc
 
-go 1.24.0
-
-toolchain go1.24.1
+go 1.24.7
 
 require (
 	github.com/antlr4-go/antlr/v4 v4.13.1
@@ -48,6 +46,7 @@ require (
 	github.com/pingcap/failpoint v0.0.0-20240528011301-b51a646c7c86 // indirect
 	github.com/pingcap/log v1.1.0 // indirect
 	github.com/rogpeppe/go-internal v1.10.0 // indirect
+	github.com/sqlc-dev/doubleclick v1.0.0 // indirect
 	github.com/stoewer/go-strcase v1.2.0 // indirect
 	github.com/wasilibs/wazero-helpers v0.0.0-20240620070341-3dff1577cd52 // indirect
 	github.com/xeipuuv/gojsonpointer v0.0.0-20180127040702-4e3ac2762d5f // indirect

go.sum

@@ -157,6 +157,8 @@ github.com/spf13/cobra v1.10.2/go.mod h1:7C1pvHqHw5A4vrJfjNwvOdzYu0Gml16OCs2GRiT
 github.com/spf13/pflag v1.0.9/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
 github.com/spf13/pflag v1.0.10 h1:4EBh2KAYBwaONj6b2Ye1GiHfwjqyROoF4RwYO+vPwFk=
 github.com/spf13/pflag v1.0.10/go.mod h1:McXfInJRrz4CZXVZOBLb0bTZqETkiAhM9Iw0y3An2Bg=
+github.com/sqlc-dev/doubleclick v1.0.0 h1:2/OApfQ2eLgcfa/Fqs8WSMA6atH0G8j9hHbQIgMfAXI=
+github.com/sqlc-dev/doubleclick v1.0.0/go.mod h1:ODHRroSrk/rr5neRHlWMSRijqOak8YmNaO3VAZCNl5Y=
 github.com/sqlc-dev/mysql v0.0.0-20251129233104-d81e1cac6db2 h1:kmCAKKtOgK6EXXQX9oPdEASIhgor7TCpWxD8NtcqVcU=
 github.com/sqlc-dev/mysql v0.0.0-20251129233104-d81e1cac6db2/go.mod h1:TrDMWzjNTKvJeK2GC8uspG+PWyPLiY9QKvwdWpAdlZE=
 github.com/stoewer/go-strcase v1.2.0 h1:Z2iHWqGXH00XYgqDmNgQbIBxf3wrNq0F3feEy0ainaU=

internal/compiler/engine.go

@@ -7,6 +7,7 @@ import (
 	"github.com/sqlc-dev/sqlc/internal/analyzer"
 	"github.com/sqlc-dev/sqlc/internal/config"
 	"github.com/sqlc-dev/sqlc/internal/dbmanager"
+	"github.com/sqlc-dev/sqlc/internal/engine/clickhouse"
 	"github.com/sqlc-dev/sqlc/internal/engine/dolphin"
 	"github.com/sqlc-dev/sqlc/internal/engine/postgresql"
 	pganalyze "github.com/sqlc-dev/sqlc/internal/engine/postgresql/analyzer"
@@ -82,6 +83,10 @@ func NewCompiler(conf config.SQL, combo config.CombinedSettings, parserOpts opts
 		c.parser = dolphin.NewParser()
 		c.catalog = dolphin.NewCatalog()
 		c.selector = newDefaultSelector()
+	case config.EngineClickHouse:
+		c.parser = clickhouse.NewParser()
+		c.catalog = clickhouse.NewCatalog()
+		c.selector = newDefaultSelector()
 	case config.EnginePostgreSQL:
 		parser := postgresql.NewParser()
 		c.parser = parser

internal/config/config.go

@@ -51,9 +51,10 @@ func (p *Paths) UnmarshalYAML(unmarshal func(interface{}) error) error {
 }
 
 const (
-	EngineMySQL      Engine = "mysql"
-	EnginePostgreSQL Engine = "postgresql"
-	EngineSQLite     Engine = "sqlite"
+	EngineMySQL       Engine = "mysql"
+	EnginePostgreSQL  Engine = "postgresql"
+	EngineSQLite      Engine = "sqlite"
+	EngineClickHouse  Engine = "clickhouse"
 )
 
 type Config struct {

internal/engine/clickhouse/catalog.go

@@ -0,0 +1,16 @@
+package clickhouse
+
+import (
+	"github.com/sqlc-dev/sqlc/internal/sql/catalog"
+)
+
+func NewCatalog() *catalog.Catalog {
+	def := "default" // ClickHouse default database
+	return &catalog.Catalog{
+		DefaultSchema: def,
+		Schemas: []*catalog.Schema{
+			defaultSchema(def),
+		},
+		Extensions: map[string]struct{}{},
+	}
+}